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Thin films with thicknesses in the range between ca. 10–50 nm of the spin crossover (SCO) compound {Fe(pyrazine)[μ4-M(CN)4]} (M = Ni, Pt) have been deposited on fused silica substrates using a sequential assembly method and 4-pyridinecarboxylic acid as anchoring layer. Film morphology and crystallinity were assessed by means of atomic force microscopy and grazing incidence X-ray diffraction, respectively. The intensity of the π–π* transition of the pyrazine ligand at 270 nm, being rather insensitive to the spin state of the complex, was used to follow the film growth as a function of different deposition parameters. On the other hand, the spin state changes were inferred from the temperature dependence of absorption bands appearing at 540, 490 and 310 nm in the low spin state. In line with their amorphous nature, each film displays a very gradual thermal spin crossover between ca. 100–300 K, independently of its thickness and deposition conditions. These results are not only interesting to better understand the effects of size reduction and organization on the SCO phenomenon, but the deposition of these SCO compounds on electrically insulating and/or optically transparent oxide surfaces opens also the door for various photonic or electronic applications. [ABSTRACT FROM AUTHOR]

This article addresses the impact of metal–ligand redox cooperativity on the functionalisation of coordinated ligands. It demonstrates the structure–reactivity correlation of bis(aldimine) derived bis-bidentate L (Py-CH＝N–(CH2)n–N＝CH-Py, with n = 2 (L1), 3 (L2), 4 (L3)) as a function of the conformation (syn/anti) of its alkylene linker as well as the overall structural form (cis/trans) of (acac)2RuII(μ-L)RuII(acac)2 complex moieties (1–5) possessing an electron-rich acetylacetonate (acac) co-ligand. A systematic variation of the bridging alkylene unit of L in RuII/RuII-derived 1–5 led to the following reactivity/redox events, which were validated through structural, spectroscopic, electrochemical and theoretical evaluations: (i) Cyclisation of the ethylene linked (syn conformation) bis-aldimine unit of L1 via C–C coupling yielded pyrazine bridged (acac)2RuII(μ-L1′)RuII(acac)2, 1a, while the corresponding anti-form (ethylene linker) of the metal-bound L1 in 2 ((acac)2RuII(μ-L1)RuII(acac)2) led to oxygenation at the ligand backbone (bis-aldimine (L) → bis(carboxamido) (L′′)) via O2 activation to generate RuIIIRuIII-derived (acac)2RuIII(μ-L1′′2−)RuIII(acac)2 (2a). (ii) Consequently, propylene and butylene linked L2 and L3 bridged between two {Ru(acac)2} units in 3 and 4/5 underwent oxygenation of L to L′′ to yield diruthenium(III) complexes 3a and 4a/5a, respectively. (iii) In contrast, analogous L bridged oxidised [(acac)2RuIII(μ-L)RuIII(acac)2](ClO4)2 ([2](ClO4)2–[5](ClO4)2) and [{(PPh3)2(CO)(H)RuII}2(μ-L)](ClO4)2 ([6](ClO4)2–[8](ClO4)2) involving electron poor co-ligands failed to undergo the oxygenation of L irrespective of its n value, reemphasising the effective role of redox interplay between RuII and L particularly in the presence of an electron-rich acac co-ligand in the functionalisation of the latter in 1a–5a. [ABSTRACT FROM AUTHOR]

Five new mononuclear ruthenium(II) tris-ligated complexes have been synthesised, varying through the choice of azine in the family of 3-azinyl-4-(4-methylphenyl)-5-phenyl-4H-1,2,4-triazole ligands (Lazine): [Ru(Lpyridine)](PF6)2 (1), [Ru(Lpyridazine)](PF6)2 (2), [Ru(L4-pyrimidine)](PF6)2 (3), [Ru(Lpyrazine)](PF6)2 (4), [Ru(L2-pyrimidine)](PF6)2 (5). Three of them, 1·2MeCN·Et2O, 3·2MeCN·Et2O and 4·2MeCN, have been structurally characterised, confirming the presence of the meridional isomer, as was previously reported for the FeII analogues. Cyclic voltammetry studies, in dry CH3CN vs. Ag/0.01 M AgNO3, show that all five RuII complexes undergo a reversible RuIII/RuII process, with the midpoint potential (Em) increasing from 0.87 to 1.18 V as the azine is changed: pyridine < pyridazine < 2-pyrimidine < 4-pyrimidine < pyrazine. A strong inverse linear correlation (R2 = 0.98) is found between the RuIII/RuII redox potential and the calculated HOMO orbital energies, which is consistent with the expectation that it is easier to oxidise (lower Em) a metal ion with a higher HOMO orbital energy. The same trend was reported earlier for the family of analogous FeII complexes, albeit at lower values of Em in all cases. In addition, the ionisation potentials of the RuII complexes, as well as those of the other group 8 analogues (FeII and OsII), showed a linear relationship with Epa. As the MIII/II redox potentials of a family of complexes has been previously reported to correlate with ligand pKa values, a computational protocol to calculate, in silico, the pKa of the Lazine family of ligands was developed. A strong linear relationship was found between the readily calculated pKa of the Lazine ligand and the Epa of the MII complex, for all three families of complexes (R2 = 0.98). [ABSTRACT FROM AUTHOR]

A series of phosphorescent platinum(II) complexes containing various phenyldiazine-type bidentate N^C ligands have been successfully synthesized and characterized. Structural modifications have been made to bidentate cyclometalating ligands regarding the nature of the diazine ring (pyrimidine, pyrazine and quinazoline), the substituent groups at the C4 position of the pyrimidine ring (OCH3, CF3) and the EDGs at the para position of the Pt atom (OCH3, Ph, NPh2, carbazol). In addition, the electronic properties of the azaheterocyclic ancillary ligand have been modulated in this series of complexes (pyridine, 4-methoxy-pyridine or pyrimidine). X-ray diffraction studies have been performed on three complexes, revealing Pt(II) ions in a distorted square-planar geometrical environment with no Pt(II)⋯Pt(II) interactions but with moderate π–π interactions in the solid-state structure. Electrochemical and computational studies suggest a ligand-centered reduction on the diazine ligands with, in some cases, additional contribution from the azaheterocyclic ancillary ligand, whereas oxidation occurs on the Pt-phenyl ring substituent moieties. All complexes exhibit phosphorescence emission ranging from green to red/near-infrared, both in solution and in the solid state. Complexes bearing a 2-(3-methoxyphenyl)pyrimidine ligand show the best PLQY of the series, up to 52% in a CH2Cl2 solution and 20% in the solid state. Furthermore, the solid state PLQY of one of the near-infrared emitting phenylquinazoline complex has been found to be 6%. [ABSTRACT FROM AUTHOR]

In this work, a series of butterfly-like isomers named oxacalix[2]naphthalene[2]pyrazine (ONP) were conveniently synthesized by a one-step catalyst-free reaction in a facile manner, and they exhibit typical characteristics of aggregation-induced emission (AIE). The mechanism study shows that restriction of intramolecular vibration (RIV) is the reason for their AIE properties. The pyrazine groups endow ONP molecules with good coordination ability, which makes them ideal ligands for constructing metal–organic frameworks (MOFs). Thus, three ONP-based luminescent MOFs were constructed, and they exhibit intense emission with lifetimes in the order of microseconds. More importantly, different ONP isomers have different binding capacities, and thus only one kind of MOF can be obtained even when using an isomer mixture of ONP ligands. This result suggested that the conformation of ONPs is an important determining factor for their application as bridging ligands. This work not only reports a series of new RIV-type AIEgens, but also offers a new platform for the construction of luminescent MOFs. [ABSTRACT FROM AUTHOR]

Metal ions (Ag+, Cd2+, Eu3+, Sm3+) and protons can, through coordination and protonation, modulate in three specific ways the structural information contained in the pyrazine-based heterocyclic strand L (obtained from 2,5-bis(methylhydrazino)pyrazine and 2 equivalents of 2-pyridinecarboxaldehyde), thus generating two linear rod-like conformations and a bent one. This conformational diversity is associated with a structural one that consists of two diprotonated forms (H2L(PF6)2 and H2L(CF3SO3)2), a polymeric architecture [AgL]n(CF3SO3)n, two rack-like complexes ([Eu2H2L3(CF3SO3)6](PF6)2 and [Sm2H2L3(CF3SO3)6](PF6)2) and a grid-like structure ([Cd4L4](CF3SO3)8). [ABSTRACT FROM AUTHOR]

Herein we report on the synthesis of (HPyz+)2[UO2Cl3(H2O)(Pyz)0.5]2·2H2O which features a novel pyrazine-bridged uranyl dimer, [UO2Cl3(H2O)(Pyz)0.5]22−. A rigorous computational and experimental analysis of this compound was performed to fully explore the influence of coordination on the electronic structure and potential charge-transfer characteristics of this dimer, revealing a delocalized π-system across the bridging pyrazine and the axial components of both uranyl centers. Electrostatic surface potentials, used to rationalize the observed assembly, indicate a decreased basicity of the uranyl oxo versus [UO2Cl4]2−, and signify a lessened capacity for the terminal –yl oxos of the [UO2Cl3(H2O)(Pyz)0.5]22− dimer to participate in supramolecular assembly. A combined density functional theory (DFT) and quantum theory of atoms in molecules (QTAIM) analysis further evidenced an increase in U＝O bond strengths within the dimer, which is supported by a blue shift in the characteristic Raman-active uranyl symmetric stretch (ν1) with respect to the more typically observed [UO2Cl4]2−. [ABSTRACT FROM AUTHOR]

The crystal structure and magnetic properties of two all-pyrazine-bridged antiferromagnetic spin ladders are reported. The complexes, catena-(bis(3-X-4-pyridone)(μ-pyrazine)copper(II)(-μ-pyrazine)diperchlorate ([Cu(pz)1.5(L)2](ClO4)2 where L = 3-X-4-pyridone and X = Br (1) or Cl (2)), contain copper(II)-based ladders in which both the rung and rail bridges are pyrazine molecules bonded through the x2–y2 orbital of the copper(II) ions. This structural scaffold is proposed to approach the isotropic spin-ladder regime. 1 and 2 crystallize in the monoclinic space group P21/c. Due to the bulk of the 3-X-4-HOpy ligands, the ladders are well isolated in the a-direction (1, 15.6 Å; 2, 15.5 Å). The ladders, which run in the b-direction, are stacked in the c-direction with the separation (1, 7.87 Å; 2, 7.82 Å) between copper(II) ions caused by the bulk of a semi-coordinate perchlorate ion coordinated in the axial position. Computational evaluation of magnetic JAB couplings between Cu-moieties of 2 supports the experimentally proposed magnetic topology and agrees with an isolated isotropic spin-ladder (Jrail = −4.04 cm−1 (−5.77 K) and Jrung = −3.89 cm−1 (−5.56 K)). These complexes introduce a convenient scaffold for synthesizing isotropic spin-ladders with modest superexchange interactions, the strength of which may be tuned by variations in L. The magnetic susceptibility down to 1.8 K, for both compounds, is well described by the strong-rung ladder model giving nearly isotropic exchange with Jrung ≈ Jrail ≈ −5.5 K (1) and −5.9 K (2) using the Hamiltonian. Theoretical simulations of the magnetic response of 2 using the isotropic ladder model are in excellent agreement with experiment. The measured magnetization to 5 T indicates a quantum-dominated magnetic spectrum. Again, calculated lower and saturation (4.3 and 24 T, respectively) critical fields for 2 are consistent with experimental measurements, and magnetization data at very low temperatures indeed suggest the presence of quantum effects. Further, the computational study of short- and long-range spin ordering indicates that a 2D-to-3D crossover might be feasible at lower temperatures. Analysis of the Boltzmann population corroborates the presence of accessible triplet states above the singlet ground state enabling the aforementioned 2D-to-3D crossover. [ABSTRACT FROM AUTHOR]

Novel water-soluble dihydroxophosphorus(V) complexes of sulphophenyl substituted porphyrazine (6), corrolazine (7) and its pyrazine fused derivative (8) were prepared and their spectral, acid–base and photophysical properties in aqueous solutions were studied. Due to the presence of eight SO3H groups, the compounds were fully monomeric (7 and 8) or only slightly aggregated (6) in water. Spectrophotometric titration revealed that the two stage deprotonation of axially bonded hydroxy groups can be achieved for porphyrazine 6 (pKa1 = 5.62, pKa2 = 9.13) and pyrazine fused corrolazine 8 (pKa1 = 6.5, pKa2 = 11.7), while only the first dissociation stage could be observed for corrolazine 7 (pKa1 = 9.94). The fluorescence emission of the corrolazines 7, 8 and especially porphyrazine 6 was low in water (ΦF = 0.086, 0.18, and 0.014, respectively) and completely quenched under basic conditions due to photoinduced electron transfer. In comparison with porphyrazine 6, the contraction of the macrocycle in the corrolazines 7 and 8 induced significant improvement of singlet oxygen production in water reaching values of ΦΔ = 0.56 and 0.43, respectively, which makes the corrolazines promising photosensitizers for photodynamic therapy. The observed evolution of the electronic absorption spectra and fluorescence quenching observed in a basic medium was explained using the model DFT calculations (cc-pvtz basis set) performed for the dihydroxophosphorus(V) complexes of unsubstituted porphyrazine and corrolazine and their mono- and doubly deprotonated forms. [ABSTRACT FROM AUTHOR]

We describe herein the first examples of six-coordinate CoII single-ion magnets (SIMs) based on the β-diimine Mebik ligand [Mebik = bis(1-methylimidazol-2-yl)ketone]: two mononuclear [CoII(Rbik)2L2] complexes and one mixed-valence {Co III2 CoII}n chain of formulas [CoII(Mebik)(H2O)(dmso)(μ-NC)2Co III2 (μ-2,5-dpp)(CN)6]n·1.4nH2O (3) [L = NCS (1), NCSe (2) and 2,5-dpp = 2,5-bis(2-pyridyl)pyrazine (3)]. Two bidentate Mebik molecules plus two monodentate N-coordinated pseudohalide groups in cis positions build somewhat distorted octahedral surroundings around the high-spin cobalt(II) ions in 1 and 2. The diamagnetic [Co III2 (μ-2,5-dpp)(CN)8]2− metalloligand coordinates the paramagnetic [CoII(Mebik)(H2O)(dmso)]2+ complex cations in a bis-monodentate fashion to afford neutral zigzag heterobimetallic chains in 3. Ab initio calculations, and cryomagnetic dc (2.0–300 K) and ac (2.0–12 K) measurements as well as EPR spectroscopy for 1–3 show the existence of magnetically isolated high-spin cobalt(II) ions with D values of 59.84–89.90 (1), 66.32–93.90 (2) and 70.40–127.20 cm−1 (3) and field-induced slow relaxation of the magnetization, being thus new examples of SIMs with transversal magnetic anisotropy. The analysis of their relaxation dynamics reveals that the relaxation of the magnetization occurs by the Raman (with values of the n parameter covering the range 6.0–6.8) and direct spin-phonon processes. [ABSTRACT FROM AUTHOR]

The mechanisms of the dearomative diborylation of pyrazines were investigated via a combination of density functional theory (DFT) calculations and experimental studies. DFT calculations revealed that a non-radical mechanism involving two successive [3,3]-σ-rearrangement-type processes is responsible for the diborylation of pyrazine with bis(pinacolato)diboron (B2pin2). However, this non-radical process is highly unfavorable for the diborylation reaction of sterically hindered pyrazine (2,3-dimethylpyrazine). For the diboration reaction of 2,3-dimethylpyrazine with B2pin2 in the presence of 2,6-dichloro-4,4′-bipyridine as the catalyst, 4,4′-bipyridine-mediated radical pathway proceeding through a B–B homolytic cleavage/boryl radical addition is preferred. Control experiments combined with kinetic studies provided supportive evidence for the proposed mechanism. [ABSTRACT FROM AUTHOR]

A praseodymium(III)-containing arsenotungstate K16H15Li7[Pr2(H2O)3(pzdc)As3W29O103]2·38H2O (1) (pzdc = pyrazine-2,3-dicarboxylic acid) was synthesized by a conventional aqueous solution method and characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD), and single crystal X-ray diffraction. Structural analysis revealed that compound 1 was constructed by two identical subunits {Pr2(H2O)3(AsW9O33)3W2O4} bridged together by two pzdc ligands. In addition, compound 1 could act as an efficient catalyst for the epoxidation of olefins and oxidation of alcohols with hydrogen peroxide (H2O2) as the oxidant. In particular, the turnover frequency (TOF) in the oxidation of 1-phenylethanol reached up to 10 170 h−1, which is higher than that of previously reported catalysts. [ABSTRACT FROM AUTHOR]

A series of new type hybrid bromobismuthates formed by various pyrazinium cations were isolated and studied. In the systems initially containing iodide anions and monocations of substituted pyrazines, the complexes based on doubly charged cations of substituted pyrazines instead of ones based on the corresponding monocations were surprisingly formed. The variation of substituted pyrazinium cations affects not only the crystal structures of hybrid bromobismuthates via tuning the nuclearity of the anions but also the hydrolytic stability of the compounds. A thorough structural study of hydrolytic transformations was performed for halobismuthates for the first time. The results revealed a stepwise course of the process affording several products. Spectral studies of the complexes evidence that the values of optical band gaps (Eg) are low in comparison with those for similar systems which is most likely due to the cooperative effect involving the nature of the corresponding cations together with the features of the supramolecular structures of the complexes. [ABSTRACT FROM AUTHOR]

Two new Evans–Showell-type polyoxometalate (POM)-based metal–organic complexes, namely {Cu3(L1)1.5(H2O)5[Co2Mo10H4O38]}·5H2O (1), {[Cu(L2)0.5(H2O)2]2[Co2Mo10H4O38]}·6H2O (2) (L1 = N,N′-bis(2-pyrazinecarboxamide)-1,4-butane, L2 = N,N′-bis(2-pyrazinecarboxamide)-1,6-hexane), were successfully synthesized and structurally characterized by single-crystal X-ray diffraction, elemental analysis, IR spectroscopy, powder X-ray diffraction (PXRD) and thermogravimetric analyses (TGA). In complex 1, the adjacent [Co2Mo10H4O38]6− polyoxoanions are linked by CuII ions to form a 1D Cu–[Co2Mo10H4O38]6− inorganic chain, which is further linked by ligand L1 and [Co2Mo10H4O38]6− polyoxoanions, forming a 3D metal–organic framework. In complex 2, the adjacent [Co2Mo10H4O38]6− polyoxoanions link the CuII ions to generate a 2D Cu–[Co2Mo10H4O38]6− inorganic layer, which is further connected with bidentate ligands L2 to obtain a 3D metal–organic framework. The structural diversities of compounds 1 and 2 showed that the spacer lengths of the flexible bis-pyrazine–bis-amide ligands play important roles in tuning the structures of the title complexes. Compounds 1 and 2 represent the first examples of 3D frameworks based on the Evans–Showell-type polyoxoanions and Cu-bis-pyrazine–bis-amide coordination complexes. Moreover, the ligand L1 was first successfully introduced into the POM system. The electrochemical and fluorescence properties of compounds 1 and 2 were discussed. As heterogeneous catalysts, compounds 1 and 2 have good catalytic activity for the oxidation of benzyl alcohol. Moreover, compound 2 has higher catalytic performance with 100% conversion and 98.0% selectivity for benzoic acid at 10 h. The difference in their catalytic performance may be mainly due to the difference of their structures. The catalysts can be recovered and reused without displaying any significant loss of activity. [ABSTRACT FROM AUTHOR]

Three isostructural coordination polymers of the formula [MCl2(DMSO)2(pz)]n (pz = pyrazine, DMSO = dimethyl sulfoxide, M = Mn, Fe and Co for 1–3) were synthesized through the solvothermal reaction of MCl2, DMSO and pz. By introducing DMSO and chloride as electron donor ligands and pz as an accepter, a donor–metal–accepter (D–M–A) system was constructed. Radicals generated by photoinduced electron transfer (PET) from a donor to an accepter result in a dramatic change of vibronic absorption spectra in UV regions and remarkable enhancement of magnetic susceptibility. The mechanism of PET was also determined by PXRD, IR, EPR and XPS measurements. This is the first example of bridging pz complexes which exhibit both photochromism and photomagnetism in a PET process. [ABSTRACT FROM AUTHOR]

A new series of alkaline-earth-metal based coordination polymers were synthesized by using a pyrazine-2,5-dicarboxylic acid (2,5-H2pzdc) ligand under hydrothermal conditions. These compounds show a variety of structural topologies, reflecting the variable coordination geometries of the alkaline-earth ions as well as the key role of the metal precursor salts. Ca, Sr, and Ba give porous three-dimensional compounds, namely [Ca(2,5-pzdc)(H2O)2]·H2O (1), [Sr(2,5-pzdc)(H2O)4]·H2O (3), [Ba(2,5-pzdc)(H2O)4]·2H2O (4) and [Ba(2,5pzdc)(H2O)2] (5), that feature one-dimensional hydrophilic channels which are filled with water molecules. The Sr compound retains its structure when the lattice water molecules are removed, while the other compounds undergo a structural rearrangement. The hydrophilicity of the Sr compound combined with its high stability even in the absence of guest molecules are the key characteristics that determine its good water adsorption and proton conductivity properties. [ABSTRACT FROM AUTHOR]

A series of novel isomorphic mononuclear complexes [Ln(PyrCOO)(acac)2(H2O)2] (Ln = Eu (1), Gd (2), Tb (3), Dy (4), Ho (5), Er (6), Tm (7), Yb (8), Y(9); acac−– acetylacetonate (pentane-2,4-dionate) anion, PyrCOOH is pyrazine-2-carboxylic acid) were prepared. Slow magnetic relaxation indicating SMM behavior was found in complexes 3, 4, 6 and 8. For 4 (Dy), the anisotropy barrier is Δeff/kB = 77 K under a dc field of 1500 Oe. For 8 (Yb), the anisotropy barrier is Δeff/kB = 54 K under a dc field of 2000 Oe which is the highest presently known value for molecular Yb carboxylate complexes and for Yb molecular complexes in general. [ABSTRACT FROM AUTHOR]

The employment of pyrazine (pyz), pyrimidine (pym) and s-triazine (triz) ligands in ReIV chemistry leads to the isolation of a family of complexes of general formula (NBu4)2[(ReX5)2(μ-L)] (L = pyz, X = Cl (1) or Br (2); L = pym, X = Br (3); L = triz, X = Br (4)). 1–4 are dinuclear compounds where two pentahalorhenium(iv) fragments are connected by bidentate pyz, pym and triz ligands. Variable-temperature magnetic measurements, in combination with detailed theoretical studies, uncover the underlying magneto-structural correlation whereby the nature of the exchange between the metal ions is dictated by the number of intervening atoms. That is, the spin-polarization mechanism present dictates that odd and even numbers of atoms favour ferromagnetic (F) and antiferromagnetic (AF) exchange interactions, respectively. Hence, while the pyz ligand in 1 and 2 mediates AF coupling, the pym and triz ligands in 3 and 4 promote F interactions. [ABSTRACT FROM AUTHOR]

Four new quasi-1D Ni2-lantern chain complexes of the form [Ni2(SOCR)4(L)]∞ (R = Ph, L = DABCO (1); R = Ph, L = pyz (2); R = CH3, L = DABCO (3); R = CH3, L = pyz (4)) were prepared from the reaction of [Ni2(SOCR)4(EtOH)], R = CH3 or Ph, with the N,N′-donor bridging ligands pyrazine (pyz) or 1,4-diazabicyclo[2.2.2]octane (DABCO). Reaction of [Ni2(tba)4(EtOH)], (tba = thiobenzoate) with the mono-N donor ligand quinuclidine (quin) gave the discrete Ni2-lantern complex [Ni2(tba)4(quin)] (5), whereas reaction with pyridine led to fragmentation of the lantern and formation of the known [Ni(tba)2(py)2] (6). Single-crystal X-ray diffraction reveals 2–4 to be 1D chain complexes comprising DABCO or pyz ligands which bridge the Ni2-lantern units. Complex 5 forms dimers through two equivalent Ni…S interactions. The Ni–Ni distances within the Ni2-lanterns are 2.5316(18)–2.595(2) Å for the 1D chain complexes 2–4, and 2.5746(4) Å in the dimeric complex 5, respectively. Comparing the solid state magnetism of 5 to precursor [Ni2(tba)4(EtOH)] demonstrates a change in coupling upon change of capping ligand. Meanwhile, chains 1–4 exhibit magnetic properties consistent with an S = 1 system, due to a mixed valent system where the two Ni centers differ in spin state, while 5 possesses two S = 1 Ni(ii) centers. DFT calculations confirm low-spin S = 0 {NiS4} and high-spin S = 1 {NiO4} centers in each lantern. Fits to the magnetic susceptibility data of the chains suggest a weak antiferromagnetic mean field interaction is present that is largely 1-D in nature, though neither pyrazine nor DABCO promote significant magnetic interaction between neighboring Ni2-lanterns. [ABSTRACT FROM AUTHOR]

The intercalation of different pyrazines (pyrazine, methylpyrazine, 2,5-dimethylpyrazine, 2,3-dimethylpyrazine, trimethylpyrazine and tetramethylpyrazine) into the trans-1,4-cyclohexanedicarboxylate (CDC2−) based Al-MOF [Al(OH)(CDC)], denoted as CAU-13, was investigated. The adsorption of the guest molecules into the flexible MOF was carried out from an aqueous solution or via vapour phase adsorption, starting with the hydrated narrow-pore form of the framework [Al(OH)(O2C-C6H10-CO2)]·H2O (CAU-13-np). The obtained host–guest systems were characterised by thermogravimetry and vibrational spectroscopy and their crystal structures were elucidated using powder X-ray diffraction (PXRD) data. The crystal structures indicate that guest molecules forming hydrogen-bonds with the host framework (pyrazine, methylpyrazine and 2,5-dimethylpyrazine) induce a slight opening of the channels, resulting in a semi-open framework conformation (CAU-13-so). For the bulkier guests 2,3-dimethylpyrazine, trimethylpyrazine and tetramethylpyrazine, only van der Waals interactions can be observed between the host and the guest molecules and a large pore conformation is observed (CAU-13-lp). We carried out in situ PXRD studies using synchrotron radiation during the adsorption of the respective guest molecules from aqueous solutions with various concentrations and at different temperatures. In general, stronger host–guest interactions required milder adsorption conditions while harsher conditions nevertheless accelerated the conversion. The kinetic parameters for the intercalation of pyrazine indicate that the rate limiting step differs, depending on the intercalation temperature. [ABSTRACT FROM AUTHOR]

Through the use of conjugate ring-rich pyrazine and quinoxaline derivatives, five new Keggin polymolybdate based compounds, [AgI3L12(H2O)2(PMo12O40)] (1), [AgI4L15(SiMo12O40)] (2), [AgI6L26(PMo12O40)2] (3), [AgI2L22(C16H36N)2](SiMo12O40)] (4), [CuI3L23(PMo12O40)] (5) (L1 = 2,3-diphenylpyrazine, L2 = 2,3-diphenylquinoxaline, C16H36N = tetrabutylammonium), were synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction. In compound 1, three AgI ions are fused by two L1 molecules to form a [Ag3L12]3+ subunit, and these subunits link the PMo12 anions to construct two kinds of 1D chains (I and II). Chains I and II connect to each other by sharing the same PMo12 anions and a 2D grid-like layer is built. The asymmetric unit of compound 2 is linked to form a dimer by sharing Ag ions, and a 1D double strand is formed. The SiMo12 anions connect adjacent 1D double strands through Ag3–O23 bonds and a 2D network is built. In compound 3, there exists a 1D ladder-like double chain with PMo12 anions as linking bars. A 2D layer is formed by linkage Ag2–O24 between adjacent chains. In compound 4, the PMo12 anions act as inorganic linkages to connect adjacent zigzag chains through Ag1–O3 bonds to construct a 2D grid-like layer. In compound 5 two CuI–L2 lines are fused by PMo12 anions to build a 1D ladder-like chain. Additionally, the electrochemical and photocatalytic properties of the title compounds have been studied. [ABSTRACT FROM AUTHOR]

Heterodimetallic Ru–Fe complexes [(tppz)(PPh3)2RuL](ClO4) (L = C≡CFc, [1](ClO4); C≡C–C6H4–C≡CFc), [2](ClO4); C≡C–C6H4–C6H4–C≡CFc, [3](ClO4)) were synthesized by the reactions of [(tppz)(PPh3)2RuCl](ClO4) (tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine) with ferrocence-acetylide ligands and characterized by ESI-MS, and 1H and 31P NMR spectroscopies. The structure of [1](PF6) was determined by X-ray crystallography. The electrochemical studies show that compounds [1](ClO4)–[3](ClO4) possess two widely separated anodic peaks, ascribable to one-electron oxidation of Fc and RuII, respectively. This assignment is further corroborated by the results of UV-vis-NIR, XPS, and theoretical calculation studies. Compound [1](ClO4) exhibits significant Ru…Fe metal–metal interactions across the Ru–C≡C–Fc backbone. As revealed by electrochemical, spectroscopic and theoretical computational studies, one-electron oxidized species [1a](ClO4)2 is between the electronically delocalized and valence-trapped state and shows a typical Robin–Day class II mixed-valence behavior. [ABSTRACT FROM AUTHOR]

Replacing the benzene spacer in the organic linker 5,5′-(benzene-1,4-diyl)diisophthalate with the nitrogen containing heterocyclic rings, namely, pyrazine, pyridazine, and pyrimidine results in three organic linkers, which were reacted with copper ions under solvothermal conditions to form three isostructural metal–organic frameworks (ZJNU-46, ZJNU-47 and ZJNU-48) exhibiting exceptionally high sorption capacities with regard to acetylene due to the simultaneous immobilization of open metal sites and Lewis basic nitrogen sites in the frameworks. At 1 atm and 295 K, the gravimetric C2H2 adsorption uptakes reach 187, 213 and 193 cm3 (STP) g−1 for these three compounds. The gravimetric C2H2 adsorption amount of ZJNU-47a is the second highest reported for MOF materials. Notably, despite their same porosities, and densities of open metal sites and uncoordinated nitrogen sites, distinctly different C2H2 adsorption capacities were observed for these three compounds, which we think are mainly associated with the difference in the relative position of nitrogen atoms leading to different binding affinities of the frameworks towards C2H2 guest molecules, and thus different C2H2 adsorptions. This work demonstrates that the rational arrangement of open nitrogen sites will favorably improve the C2H2 uptake and thus provides useful information for future design of porous MOFs with high acetylene storage capacities. [ABSTRACT FROM AUTHOR]

The functionalisation of the 16-electron complex [Os(η6-p-cymene)(1,2-dicarba-closo-dodecarborane-1,2-dithiolato)] (1) with a series of Lewis bases to give the 18-electron complexes of general formula [Os(η6-p-cymene)(1,2-dicarba-closo-dodecarborane-1,2-dithiolato)(L)] (L = pyridine (2), 4-dimethylaminopyridine (3), 4-cyanopyridine (4), 4-methoxypyridine (5), pyrazine (6), pyridazine (7), 4,4′-bipyridine (8) and triphenylphosphine (9)) is reported. All 18-electron complexes are in equilibrium in solution with the 16-electron precursor, and thermochromic properties are observed in some cases (2, 3, 5, 8, and 9). The binding constants and Gibbs free energies of the equilibria are determined using UV-visible titrations and their stabilities investigated. Synthetic routes for forcing the formation of the 18-electron species are proposed, and analytical methods to characterise the equilibria are described. [ABSTRACT FROM AUTHOR]

A series of thermally stable Hofmann-type clathrate structures with the general formula M(pz)[M′(CN)4], where M and M′ are bivalent metal ions MII = NiII, CoII, MII′ = NiII, PdII, PtII, and pz is the pyrazine bidentate ligand, was synthesized and investigated for the efficient entrapment of iodine (I2) in solution and in the gas phase. Iodine-containing clathrates thus prepared were analysed to determine the saturation capacity, thermal stability, guest-induced structural changes of the clathrate's lattice and the nature of the confined iodine according to the chemical composition of the host structure. An efficient confinement of about 1 I2 per unit cell is observed for the series of clathrates with the NiII and PdII ions in the square planar position whatever the bivalent metal ion in the octahedral position. Specific responses in the lattice adjustment are detected for CoII in the octahedral and PdII in the square planar positions. [ABSTRACT FROM AUTHOR]

The syntheses and structural characterization of three new monodimensional azido-bridged manganese(ii) complexes with empirical formulae [Mn(N3)2(aminopyz)2]n (1), [Mn(N3)2(4-azpy)2]n (2) and [Mn(N3)2(4-Bzpy)2]n (3) (pyz = pyrazine (1,4-diazine)), 4-azpy = 4-azidopyridine and 4-Bzpy = 4-benzoylpyridine) are reported. 1 is a monodimensional compound with double EO azido bridges, 2 is an alternating monodimensional compound with double end-on and double end-to-end azido bridges in the sequence di-EO-di-EE and 3 is a monodimensional compound with double end-on and double end-to-end azido bridges in the sequence di-EO-di-EO-diEO-di-EO-di-EE. The magnetic properties of 1–3 are reported. Periodic DFT calculations were performed to estimate the J values and quantum Monte Carlo simulations were carried out using the calculated J values to check their accuracy in comparison with the experimental magnetic measurements. From this theoretical analysis, two appealing features of the di-EO Mn(ii) compounds can be extracted: first, the exchange coupling becomes more ferromagnetic when the Mn–N–Mn bridging angle becomes larger and the spin density of the bridging nitrogen atoms has an opposite sign to that of the Mn(ii) centers. [ABSTRACT FROM AUTHOR]

Two new Re(iv) compounds of formulae H2tppz[ReCl6] (1) and [Cu(bpzm)2(μ-Cl)ReCl3(μ-ox)Cu(bpzm)2(μ-ox)ReCl3(μ-Cl)]n (2) [tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine and bpzm = bis(pyrazolyl-1-yl)methane] have been prepared and their crystal structures determined by X-ray diffraction on single crystals. Compound 1 is a mononuclear species whose structure consists of octahedral hexachlororhenate(iv) anions and diprotonated H2tppz2+ cations which are arranged in the unit cell as alternating anionic and cationic layers, held together by electrostatic forces. The structure of 2 is made up of alternating [Cu(1)(bpzm)2]2+ and [(ox)ReCl3(μ-Cl)Cu(2)(bpzm)2(μ-Cl)ReCl3(ox)]2− entities interlinked by oxalate bridges to afford a neutral heterobimetallic chain. The oxalate group adopts the didentate (at Re)/monodentate (at Cu) bridging mode. The magnetic behavior of 1 and 2 has been investigated over the temperature range 1.9–295 K. 1 is a magnetically diluted Re(iv) complex, the relatively large value of the zero-field splitting of the ground level [D = −15.8(2) cm−1] accounting for the variation of χMT in the low temperature range. Weak intrachain ferromagnetic interactions between Re(iv) and Cu(ii) through oxalate (J1 = +0.15 cm−1) and single chloro (J2 = +4.9 cm−1) bridges occur in 2 which are obscured by the large zero-field splitting of the Re(iv) ion (DRe = 42 cm−1). In addition, interchain antiferromagnetic interactions are also involved in 2 which are responsible for the metamagnetic behavior observed, the value of the critical dc magnetic field (Hc) being 20 kOe. [ABSTRACT FROM AUTHOR]

Two new Re(iv) compounds of formulae H2tppz[ReCl6] (1) and [Cu(bpzm)2(μ-Cl)ReCl3(μ-ox)Cu(bpzm)2(μ-ox)ReCl3(μ-Cl)]n (2) [tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine and bpzm = bis(pyrazolyl-1-yl)methane] have been prepared and their crystal structures determined by X-ray diffraction on single crystals. Compound 1 is a mononuclear species whose structure consists of octahedral hexachlororhenate(iv) anions and diprotonated H2tppz2+ cations which are arranged in the unit cell as alternating anionic and cationic layers, held together by electrostatic forces. The structure of 2 is made up of alternating [Cu(1)(bpzm)2]2+ and [(ox)ReCl3(μ-Cl)Cu(2)(bpzm)2(μ-Cl)ReCl3(ox)]2− entities interlinked by oxalate bridges to afford a neutral heterobimetallic chain. The oxalate group adopts the didentate (at Re)/monodentate (at Cu) bridging mode. The magnetic behavior of 1 and 2 has been investigated over the temperature range 1.9–295 K. 1 is a magnetically diluted Re(iv) complex, the relatively large value of the zero-field splitting of the ground level [D = −15.8(2) cm−1] accounting for the variation of χMT in the low temperature range. Weak intrachain ferromagnetic interactions between Re(iv) and Cu(ii) through oxalate (J1 = +0.15 cm−1) and single chloro (J2 = +4.9 cm−1) bridges occur in 2 which are obscured by the large zero-field splitting of the Re(iv) ion (DRe = 42 cm−1). In addition, interchain antiferromagnetic interactions are also involved in 2 which are responsible for the metamagnetic behavior observed, the value of the critical dc magnetic field (Hc) being 20 kOe. [ABSTRACT FROM AUTHOR]

We present a new coordination polymer, {[VO(pzdc)(H2O)2] H2O}n, built from vanadyl and pyrazine-2,5-dicarboxylate (pzdc) ions. It consists of a one-dimensional chain of vanadyl ions linked by pzdc ions. The carboxylate groups show monodentate coordination, while the pyrazine ring is present both in non-coordinated and coordinated modes. This novel structure is stabilized by an intricate network of hydrogen bonds. The material is highly robust, and thermally stable up to 400 K. It is also antiferromagnetic, with a maximum magnetic susceptibility at ca. 50 K. The orbital shape and population analysis by means of DFT analysis confirm the π-acceptor role of the aromatic nitrogen function of the ligand, while the oxygen-based moieties (carboxylates from pzdc, the aqua ligands and oxo from V=O group) behave as normal donors. Charting the density flow related with significant transitions computed by time-dependent DFT, we determined the ligand-to-metal charge transfer processes. The topology of the chain complex implies two different types of connecting bridges. Using Broken Symmetry DFT modelling gives evidence for two different exchange coupling mechanisms between the vanadyl ions along each of these two molecular bridges. One is strongly antiferromagnetic, practically reducing the chain to ‘vanadyl dimers’. The other is almost uncoupled, due to the large distance between the vanadyl ions. [ABSTRACT FROM AUTHOR]

A bismetallo-organic polymer was successfully prepared by treating a metallo-ligand with Ag+; characterization was accomplished by NMR, UV-vis, and single crystal X-ray analyses. This heteronuclear polymer achieved more than a two-fold turnover number (TON) and a faster reaction rate in comparison to a Ce-driven Ru-monomer in catalytic water oxidation. [ABSTRACT FROM AUTHOR]

The coordinatively-unsaturated 16-electron half-sandwich precursors [Cp*M(pdt)] (M = Rh, Ir; pdt = pyrazine-2,3-dithiol) have been synthesized. X-ray crystallography in combination with 1H NMR analysis was used to elucidate the nature of the precursors. The Rh(iii) precursor displays a dimeric form in the trans arrangement in the solid state, formulated as [(Cp*Rh)2(μ(S)-pdt)2] (1), in which covalent Rh–S bonds bridge the metal centers. In solution, however, dimers 1 and monomers 2 coexist in equilibrium. The dissociation equilibrium of 1 in DMSO-d6 was evaluated by 1H NMR at several temperatures between 20 and 80 °C. The Ir(iii) precursor [Cp*Ir(pdt)] (3) is the monomeric form, and stable in the solid state and solution. Due to their unsaturation and bridging properties, these precursors were further used in stepwise assembly reactions with the binuclear building blocks to give open macrocycles and a closed molecular box. [ABSTRACT FROM AUTHOR]

The complexation of representative lanthanides with three calix[4]arenes functionalized with four pyrazine pendent arms containing different substituents such as carbamoyl dioctyl (LI), diisopropyl phosphonate (LII), and diphenyl phosphoryl (LIII) was investigated in water-saturated 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BumimTf2N) by absorption spectroscopy, luminescence spectroscopy, and microcalorimetry. All three ligands form 1 : 1 ML complexes (M = Eu3+ and L = ligand), and the stability constants (log β) follow the order: LI (−1.38 ± 0.66)

In this work the first phenazine derivatives with guanidino substituents were prepared and their structural and electronic properties studied in detail. The guanidino groups decrease the HOMO–LUMO gap, massively increase the quantum yield for fluorescence and offer sites for metal coordination. The yellow-orange colored 2,3,7,8-tetraguanidino-substituted phenazine shows intense fluorescence. The wavelength of the fluorescence signal is strongly solvent dependent, covering a region from 515 nm in Et2O solution (with a record quantum yield of 0.39 in Et2O) to 640 nm in water. 2,3-Bisguanidino-substituted phenazine is less fluorescent (maximum quantum yield of 0.17 in THF), but exhibits extremely large Stokes shifts. In contrast, guanidino-functionalized fluorenes emit only very weakly. Subsequently, the influence of coordination on the electronic properties and especially the fluorescence of the phenazine system was analysed. Coordination first takes place at the guanidino groups, and leads to a blue shift of the luminescence signal as well as a massive decrease of the luminescence lifetime. Luminescence is almost quenched completely upon CuI coordination. On the other hand, in the case of ZnII coordination the fluorescence signal remains strong (quantum yield of 0.36 in CH3CN). In the case of strong zinc Lewis acids, an excess of metal compound leads to additional coordination at the phenazine N atoms. This is accompanied by significant red-shifts of the lowest-energy transition in the absorption and fluorescence spectra. Pentanuclear complexes with two phenazine units were isolated and structurally characterized, and further aggregation leads to chain polymers. [ABSTRACT FROM AUTHOR]

Four cationic iridium(III) complexes of the form [Ir(CN)2(NN)]+ bearing either a 2,5-dipyridylpyrazine (2,5-dpp) or a 2,2':5',2''-terpyridine (2,5-tpy) ancillary ligand and either 2-phenylpyridine (ppy) or a 2-(2,4-difluorophenyl)-5-methylpyridine (dFMeppy) cyclometalating ligands were synthesized. The optoelectronic properties of all complexes have been fully characterized by UV-visible absorption, cyclic voltammetry and emission spectroscopy. The conclusions drawn from these studies have been corroborated by DFT and TDDFT calculations. The four complexes were assessed as emitters in light-emitting electrochemical cells. Complex 1a, [Ir(ppy)2(2,5-dpp)]PF6, was found to be a deep red emitter (666 nm) both in acetonitrile solution and in the electroluminescent device. Complex 2a, [Ir(ppy)2(2,5-tpy)]PF6 was found to be an orange emitter (604 nm) both in solution and in the LEEC. LEECs incorporating both of these complexes were stable over the course of around 4-6 hours. Complex 1b, [Ir(dFMeppy)2(2,5-dpp)]PF6, was also determined to emit in the orange (605 nm) but with a photoluminescent quantum yield (ΦPL) double that of 2a. Complex 2b, [Ir(dFMeppy)2(2,5-tpy)]PF6 is an extremely bright green emitter (544 nm, 93%). All four complexes exhibited quasireversible electrochemistry and all four complexes phosphoresce from a mixed charge-transfer excited state. [ABSTRACT FROM AUTHOR]

A series of pyrazine-2,3,5,6-tetracarboxylate alkali-lanthanide coordination frameworks, namely [NaLn(pztc)(H2O)3]·H2O [Ln = Ce (1), Sm (2), Eu (3), Gd (4) and Tb (5); H4pztc = pyrazine-2,3,5,6-tetracarboxylic acid], have been synthesized by reacting Ln(NO3)3·6H2O with H4pztc in the presence of NaOH at room temperature. X-ray crystallographic analysis reveals that complexes 1-5 are isostructural, featuring three-dimensional (3D) networks with a unique (411·68·8²)(4³·6²·8)(4³) topology in which the ligand displays a novel µ7-coordination mode. The photoluminescence (PL) spectra in the solid state reveal that complexes 2, 3 and 5 exhibit the characteristic luminescence of Sm(III), Eu(III) and Tb(III) ions, respectively, while complex 4 displays a broad band in the range of 400-650 nm (λmax = 505 nm) which exhibits about 103 nm red-shift and enhancement compared to the band of the free ligand. Further, the isostructural two-component Eu(III)-doped Gd(III) complexes realize color-tunable luminescence from red to yellow, white, green and blue by the variation of excitation wavelengths. They represent the first example of full-color-tunable emission in lanthanide coordination frameworks by the variation of excitation light. [ABSTRACT FROM AUTHOR]

Two novel coordination polymers [Ag16(SO4)8][Ag4(SO4)2]3(L1)12.nH2O (n = 72) (1) and [Ag10(SO4)5(L2)4- (H2O)2].8H2O (2) based on conformationally variable oligo-α-heteroarylsulfanyl ligands 2-(pyrazin- 2-ylthio)-6-(pyridin-2-ylthio)pyrazine (L1) or 2,6-bis(pyrazin-2-ylthio)pyrazine (L2) and sulfate-templated high-nuclearity Ag(I) clusters as structure-building units (SBUs) have been synthesized under mild conditions. Single-crystal X-ray analysis showed that complex 1 exhibits a porous three-dimensional framework containing Ag16(SO4)8 and Ag4(SO4)2 SBUs that are interconnected by L4 ligands, whereas 2 has a much denser network constructed from Ag10(SO4)5 SBUs and L2 linkers. To our knowledge, the Ag16(SO4)8 cluster core found in 1 is the largest sulfate-based polynuclear SBU in coordination polymers, and the 14-connected Ag10(SO4)5 in 2 is the highest-connectivity Ag(I) cluster SBU reported to date. These two complexes were fully characterized by infrared spectroscopy, elemental analysis, powder X-ray diffraction, thermogravimetric analysis and differential scanning calorimetry. [ABSTRACT FROM AUTHOR]

Two pentacobalt(II) EMACs were synthesized. A pyrazine-modulated tripyridyldiamine resulted in an EMAC with fully delocalized Co-Co bonds along molecules. From a pyrazine- and naphthyridine-containing ligand, a defective cobalt linear EMAC with an 8-coordinated cobalt(II) in the center was obtained for the first time. An electrochemistry study on the defective pentacobalt chain compound showed redox peaks at E1/2 = -1.00, +0.76, and +0.98 V (versus EAg/AgCl), indicating that it is quite stable and very resistant to both oxidation and reduction. Research on magnetism revealed that the fully delocalized Co EMAC is a spin mixture, and the defective cobalt EMAC showed a high-spin mononuclear cobalt(II) behaviour with a magnetic moment of 2.63µB per molecule at room temperature. Measurement on molecular electric conductance by STM bj showed a single-molecular resistance of 15.4 (±3.1) MO for defective and 12.3 (±2.6) MΩ for delocalized pentacobalt complexes. [ABSTRACT FROM AUTHOR]

Three octamolybdate-based metal-organic complexes (MOCs), namely, [H2en]2[Cu(pzca)2(Mo8O26)]. 4H2O (1), [Cu2(pzca)2(Mo8O26)0.5(H2O)4].H2O (2) and [CuI 3CuII 4(pzca)7(Mo8O26)(H2O)2].4H2O (3) (en = ethylenediamine, pzca = 2-pyrazinecarboxylic acid), have been successfully synthesized under hydrothermal conditions via adding different kinds of amine and adjusting the pH values. The single crystal X-ray diffraction, elemental analyses, IR spectra, and thermogravimetric analyses have been used to characterize the title complexes. In compound 1, the [Cu(pzca)2] units bridge the [β-Mo8O26]4- clusters to generate a 1D chain, which is extended by hydrogen-bonding interactions to a 3D supramolecular structure. Compound 2 exhibits a 3D coordination framework based on the 1D infinite [Cu2(pzca)2]n2n+ zigzag chains and β-Mo8O26 4- anions, and shows a trinodal 3,3,4-connected {83}4{86} topology containing a dodecagonal channel with the dimension of 13.496 × 19.642 Å2. Compound 3 is a 3D metal-organic network derived from the "λ"-like [Cu5(pzca)4] subunits and [β-Mo8O26]4- anions, which represents a novel {4.6.83.10}2{4.6.8}2{42.104}{42.83.10}{6.82}2{62.103.12}{62.82.102}{62.83.10}{63}4 topology in octamolybdate- based MOCs. The structural diversities show that the different amines and pH value of the reaction system play key roles in the construction of high dimensional architectures. Moreover, the electrochemical behaviors and photocatalytic activity for compound 1 have been investigated in detail. [ABSTRACT FROM AUTHOR]

A family of silver(I) complexes, [Ag2(L)2(OOCCF3)2] (1), [Ag(L)0.5(OOCCF3)] (2), [Ag(L)2](OOCCF3)(H2O)2 (3), was obtained by reactions of 4,4'-di(2-oxazolinyl)biphenyl (L) and AgOOCCF3 in different reaction media. Compound 1 has a 1D chain structure with alternative connections between the Ag(I) and L ligand. When the crystal nucleation inductor, pyrazine, was added into the reaction system, complex 2 was isolated with no pyrazine observed in its structure. In 2, the 1D inorganic chains formed by Ag(I) cations and OOCCF3 - anions were connected by the L ligand to produce a 2D network. When a different inductor, imidazole, was added into the reaction system, 3 with (4,4) topology was synthesized, and again no imidazole was found in 3. When 1-3 were used as catalysts for cycloaddition reactions between imino esters and methyl acrylate, 3 affords the highest yield, in which the particular size of the channels in 3 led to its selective catalytic performance. [ABSTRACT FROM AUTHOR]

The isolation and characterization of four coordination polymers obtained by direct reactions of metal ion salts of Cu(ii), Co(ii) and Fe(ii) with pyrazine (pyz) and benzoic/benzoate (Bz) ligands under hydrothermal or hydrothermal microwave conditions are described. The use of copper(ii) perchlorate as the starting salt allows us to obtain compounds in a selective way by changing the pH values giving rise to the formation of two 3D-coordination polymers: [Cu(pyz)2]ClO4·pyz (1) and [Cu2(pyz)4](ClO4)2·HBz·H2O (2). In both polymers, 4-connected Cu(i) uninodal coordination networks with significant structural differences between them, due to the templating effect of the solvation molecules and counterions, have been found. However, reactions carried out under similar conditions with MSO4 (M = Co and Fe) led to the isolation of two [M2(μ-Bz)2(μ-pyz)2(Bz)2]·(HBz) isostructural infinite 1D ladder chains (M = Co (3) and M = Fe (4)). These coordination polymers show a spin-canting antiferromagnetism and metamagnetism behaviour for Co(ii) and HS ↑ HS/LS ↑ LS spin-crossover phenomena for Fe(ii), respectively. The latter compound is the first example of a FeIIO4N2 coordination environment showing this phenomenon. [ABSTRACT FROM AUTHOR]

A new binuclear oxovanadium(v) complex [{VO(OEt)(EtOH)}2L] (1) where H4L is bis(2-hydroxybenzylidene)terephthalohydrazide has been synthesized and fully characterized. The combination of 1 with pyrazine-2-carboxylic acid (PCA; a cocatalyst) affords a catalytic system for the efficient oxidation of saturated hydrocarbons, RH, with hydrogen peroxide and air in acetonitrile solution at 50 °C to produce alkyl hydroperoxides, ROOH, as the main primary products. Very high turnover numbers (TONs) have been attained in this reaction: for example, after 2220 min, TON = 44 000 and initial TOF (turnover frequency) = 3300 h−1 per molecule of complex 1. The estimated activation energy of the cyclohexane oxygenation in the presence of 1/PCA is Ea = 16 ± 2 kcal mol−1. This value is identical to that obtained for the cyclohexane oxidation with H2O2 catalyzed by the (n-Bu4N)[VO3]/PCA combination (17 ± 2 kcal mol−1). The dependences of initial oxidation rates W0 on the initial concentrations of all components of the reaction mixture have been determined. Based on these kinetic data and on the regio- and bond-selectivity parameters measured in the oxidation of linear and branched alkanes a mechanism of the oxidation has been proposed which includes the generation of hydroxyl radicals in the crucial stage. [ABSTRACT FROM AUTHOR]

A new binuclear oxovanadium(v) complex [{VO(OEt)(EtOH)}2L] (1) where H4L is bis(2-hydroxybenzylidene)terephthalohydrazide has been synthesized and fully characterized. The combination of 1 with pyrazine-2-carboxylic acid (PCA; a cocatalyst) affords a catalytic system for the efficient oxidation of saturated hydrocarbons, RH, with hydrogen peroxide and air in acetonitrile solution at 50 °C to produce alkyl hydroperoxides, ROOH, as the main primary products. Very high turnover numbers (TONs) have been attained in this reaction: for example, after 2220 min, TON = 44 000 and initial TOF (turnover frequency) = 3300 h−1 per molecule of complex 1. The estimated activation energy of the cyclohexane oxygenation in the presence of 1/PCA is Ea = 16 ± 2 kcal mol−1. This value is identical to that obtained for the cyclohexane oxidation with H2O2 catalyzed by the (n-Bu4N)[VO3]/PCA combination (17 ± 2 kcal mol−1). The dependences of initial oxidation rates W0 on the initial concentrations of all components of the reaction mixture have been determined. Based on these kinetic data and on the regio- and bond-selectivity parameters measured in the oxidation of linear and branched alkanes a mechanism of the oxidation has been proposed which includes the generation of hydroxyl radicals in the crucial stage. [ABSTRACT FROM AUTHOR]

Solid state structures of group 13 metal halide complexes with pyrazine (pyz) of 2 : 1 and 1 : 1 composition have been established by X-ray structural analysis. Complexes of 2 : 1 composition adopt molecular structures MX3·pyz·MX3 with tetrahedral geometry of group 13 metals. Complexes of AlBr3 and GaCl3 of 1 : 1 composition are 1D polymers (MX3·pyz)∞ with trigonal bipyramidal geometry of the group 13 metal, while the weaker Lewis acid GaI3 forms the monomeric molecular complex GaI3·pyz, which is isostructural to its pyridine analog GaI3·py. Tensimetry studies of vaporization and thermal dissociation of AlBr3·pyz and AlBr3·pyz·AlBr3 complexes have been carried out using the static method with a glass membrane null-manometer. Thermodynamic characteristics of vaporization and equilibrium gas phase dissociation of the AlBr3·pyz complex have been determined. Comprehensive theoretical studies of (MX3)n·(pyz)m complexes (M = Al, Ga; X = Cl, Br, I; n = 1, 2; m = 1–3) have been carried out at the B3LYP/TZVP level of theory. Donor–acceptor bond energies were obtained taking into account reorganization energies of the fragments. Computational data indicate that the formation of (MX3·pyz)∞ polymers with coordination number 5 is only slightly more energetically favorable than the formation of molecular complexes of type MX3·pyz for X = Cl, Br. It is expected that on melting (MX3·pyz)∞ polymers dissociate into individual MX3·pyz molecules. This dovetails with low melting enthalpies of the (MX3·pyz)∞ complexes. Polymer stability decreases in the order AlCl3 ＞ AlBr3 ＞ GaCl3 ＞ AlI3 ＞ GaBr3 ＞ GaI3. For MI3·pyz complexes computations predict that the monomeric structure motif is more energetically favorable compared to the catena polymer. These theoretical predictions agree well with the experimentally observed monomeric complex GaI3·pyz in the solid state. Thus, the Lewis acidity of the group 13 halides may play a decisive role in the formation of 1D polymeric networks. [ABSTRACT FROM AUTHOR]

A new hybrid pyrazine–bipyridine ligand L (C26H20N6) and its complexes with Mn(NO3)2, Mn(ClO4)2, MnCl2 and MnBr2 have been synthesised. By the self-assembly of L and Mn(ii) ions three different kinds of supramolecular complexes have been obtained: binuclear baguette complex [Mn2L(H2O)6](NO3)4·2.5H2O 1 and tetranuclear [2 × 2] grid-type complex [Mn4L4](ClO4)8·2.5(CH3CN)·2CH3OH 2 and mononuclear complexes [MnL2]X2 (where X = Cl−3 and X = Br−4). Crystal structures and magnetic properties of Mn(ii) complexes 1 and 2 have been also investigated. The crystal structures reveal that in both 1 and 2 complexes the Mn(ii) ions have coordination number 6 and distorted octahedral coordination geometry. In 2 four metal cations and four ligands have assembled into a grid-type [2 × 2] array, with a perchlorate anion occupying the central cavity, with clearly a good fit for the center of the cavity. The perchlorate anion, in contrast to the nitrate anion, probably acts as a template in the formation of tetranuclear grid-type complexes. Magnetic susceptibility measurements indicate that the Mn(ii) ions are all high spin, and in both 1 and 2 complexes there are weak antiferromagnetic interactions between Mn(ii) ions. [ABSTRACT FROM AUTHOR]

The mono- (1) and dinuclear (2) ruthenium(ii) bis(2,2′-bipyridine) complexes of 2,5-di(pyridin-2-yl)pyrazine (2,5-dpp), for which the UV/Vis absorption and emission as well as electrochemical properties have been described earlier, are reinvestigated here by resonance, surface enhanced and transient resonance Raman spectroscopy together with selective deuteration to determine the location of the lowest lying excited metal to ligand charge transfer (3MLCT) states. The ground state absorption spectrum of both the mono- and dinuclear complexes are characterised by resonance Raman spectroscopy. The effect of deuteration on emission lifetimes together with the absence of characteristic bipy anion radical modes in the transient Raman spectra for both the mono- and dinuclear complexes bridged by the 2,5-dpp ligand confirms that the excited state is 2,5-dpp based; however DFT calculations and the effect of deuteration on emission lifetimes indicate that the bipy based MLCT states contribute to excited state deactivation. Resonance Raman and surface enhanced Raman spectroscopic (SERS) data for 1and 2are compared with that of the heterobimetallic complexes [Ru(bipy)2(2,5-dpp)PdCl2]2+3and [Ru(bipy)2(2,5-dpp)PtCl2]2+4. The SERS data for 1indicates that a heterobimetallic Ru–Au complex forms in situupon addition of 1to a gold colloid. [ABSTRACT FROM AUTHOR]

Four new [AuBr2(CN)2]−-based coordination polymers, Zn(pyz)(NCMe)2[AuBr2(CN)2]2(1; pyz = pyrazine), Co(pyz)[AuBr2(CN)2]2·H2O (2) and [M(bipy)2(AuBr2(CN)2)][nBu4N][AuBr2(CN)2]2(bipy = 4,4′-bipyridine), where M = Co (5) and Zn (6), were synthesized and three of them structurally characterized. 1forms 1-D chains connected by pyz ligands while isostructural 5and 6form 3-D frameworks via[AuBr2(CN)2]−and bipy linkers. Aqueous suspensions of 2, 5and 6or their precursors in situ(preferred) were heated hydrothermally to 125 °C, triggering the reductive elimination of bromine from the Au(iii) centres, which yielded the [Au(CN)2]−-based coordination polymers M(pyz)[Au(CN)2]2, where M = Zn (3) or Co (4) and Zn(bipy)[Au(CN)2][Au{Br0.68(CN)0.32}CN] (7), or a mixture of cyanoaurate(i)-containing products in the case of 5and 6. The structural characterization of 3revealed a [Au(CN)2]−/pyz-based framework similar to previously reported Cu(pyz)[Au(CN)2]2, whereas 7formed an intricate network consisting of individual 2-D networks held together by AuAu interactions and featuring the rare [AuBrCN]−unit. The kinetics of the thermally-induced reductive elimination of Br2from K[AuBr2(CN)2] in 1-BuOH yielded a t½of approx. 10 min to 4 h from 98 to 68 °C, and activation parameters of ΔH‡= 131(15) kJ mol−1and ΔS‡= 14.97(4) kJ K−1mol−1, indicating that the elimination of the halogen provides the highest barrier to activation. [ABSTRACT FROM AUTHOR]

A microporous metal–organic framework [Cu3(ipO)2(pyz)2]n, (ipO = 2-hydroxyisophthalic acid, pyz = pyrazine) was synthesized viaan in situ.ligand transformation reaction. The microporous framework displays helical arrays of ipo ligands holding the Cu atoms in 2D sheets, whilst the coordination of pyz molecules acts to arrange these sheets into a microporous 3D structure. Remarkable selective sorption behaviour (>5) for H2over N2is observed and explained with molecular dynamics simulations. [ABSTRACT FROM AUTHOR]

The preparation of a number of binuclear (salen)osmium phosphinidine and phosphiniminato complexes using various strategies are described. Treatment of [OsVI(N)(L1)(sol)](X) (sol = H2O or MeOH) with PPh3affords an osmium(iv) phosphinidine complex [OsIV{N(H)PPh3}(L1)(OMe)](X) (X = PF61a, ClO41b). If the reaction is carried out in CH2Cl2in the presence of excess pyrazine the osmium(iii) phosphinidine species [OsIII{N(H)PPh3}(L1)(pz)](PF6) 2can be generated. On the other hand, if the reaction is carried out in CH2Cl2in the presence of a small amount of H2O, a μ-oxo osmium(iv) phosphinidine complex is obtained, [(L1){PPh3N(H)}OsIV–O–OsIV{N(H)PPh3}(L1)](PF6)23. Furthermore, if the reaction of [OsVI(N)(L1)(OH2)]PF6with PPh3is done in the presence of 2, the μ-pyrazine species, [(L1){PPh3N(H)}OsIII–pz–OsIII{N(H)PPh3}(L1)](PF6)24can be isolated. Novel binuclear osmium(iv) complexes can be prepared by the use of a diphosphine ligand to attack two OsVIN. Reaction of [OsVI(N)(L1)(OH2)](PF6) with PPh2–CC–PPh2or PPh2–(CH2)3–PPh2in MeOH affords the binuclear complexes [(MeO)(L1)OsIV{N(H)PPh2–R–PPh2N(H)}OsIV(L1)(OMe)](PF6)2(R = CC 5, (CH2)36). Reaction of [OsVI(N)(L2)Cl] with PPh2FcPPh2generates a novel trimetallic complex, [Cl(L2)OsIV{NPPh2–Fc–PPh2N}OsIV(L2)Cl] 7. The structures of 1b, 2, 3, 4, 5and 7have been determined by X-ray crystallography. [ABSTRACT FROM AUTHOR]

The reaction of oxacalix[2]benzene[2]pyrazines 1and 2with copper(ii) nitrate, as well as dimeric copper(ii) tetraacetate are presented. Ligands 1and 2, both adopt 1,3-alternate conformation, with the two exo-Lewis basic sites spatially oriented outwards. Ligand 1reacts with copper(ii) ions generated a discrete molecular cage 3by bridging two ligands viatwo Cu2+ions in the equatorial region. While the reaction of 1with dicopper(ii) tetraacetate unit resulted in the formation of a discrete supramolecular complex 4with 1 : 2 stoichiometry between the dicopper(ii) unit and ligand 1, due to the larger size and axial coordination mode of the dicopper(ii) unit. The conformationally flexible nature of ligand 2facilitated the formation of coordination polymers 5and 6upon interaction with copper(ii) and dicopper(ii) units, respectively. Coordination polymer 5featured a zigzag structure of alternating ligand 2and Cu2+ion, while in coordination polymer 6, ligand 2serves as an axial 2-connected node, propagating the “paddlewheel” dicopper(ii) unit along the polymeric chain. [ABSTRACT FROM AUTHOR]

Three new supramolecular metal-coordination architectures [M(H2O)4(ampyz)2][M(H2O)6](SO4)2(H2O)2(M = Co (1), Fe (2), and mixed Co/Fe (3); ampyz = 2-aminopyrazine) and a Cd(ii) coordination polymer [Cd(ampyz)(H2O)2(SO4)]n(H2O)n(4) were synthesized by layered diffusion and structurally characterized. Compounds 1–3are isomorphous. Monomeric complex units [M(H2O)4(ampyz)2]2+are assembled by intermolecular hydrogen bonding and π–π stacking viaampyz moieties to build 2D sheets. These layers are linked by intermolecular hydrogen bonding viaampyz ligand, [M(H2O)6]2+unit, sulfate anion and lattice and coordinated water molecules to stabilize 3D supramolecular structure. Compound 4shows a 2D coordination network where the sulfato connector and the bridging ampyz link Cd(ii) ions. Lattice water molecules are filled in between the layers viathe hydrogen bonds stabilizing 3D supramolecular network of 4. Interestingly, compounds 1–3exhibit water-induced reversible crystal-to-amorphous transformations with chromotropism and compound 4also shows water-induced reversible structural phase transformation confirmed by spectroscopic techniques, elemental analyses, TGA, and XRPD. These results demonstrate the significant role between coordination bridges and weaker intermolecular interactions for the structural conversion even though 1–3lack coordination bridges for the maintenance of their structures, however, the weak intermolecular interactions, especially hydrogen bonding, play a key role to the recovery of the crystalline phase. [ABSTRACT FROM AUTHOR]