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A dodecanuclear [Ni8Ca4] compound, [Ni8(L)8Ca4(CO3)4(dmf)5.5(H2O)6.5]·20H2O (1) (dmf = dimethylformamide) has been prepared by the reaction of a polydentate ligand (E)-2-(2-hydroxy-3-methoxybenzylidene)amino-4-nitrophenol (H2L) with NiCl2·6H2O, CaCl2·2H2O and Na2CO3 in dmf at room temperature. The solid-state molecular structure of compound 1 was determined by single crystal X-ray crystallography. Compound 1 consists of a [Ni8Ca4] coordination wheel with eight NiII ions and four CaII ions assembled by four carbonates and eight deprotonated L2− ligands. The asymmetric unit of compound 1 contains two NiII ions, one CaII ion, two coordinated deprotonated Schiff base ligands (L2−), one coordinated carbonate ion, two coordinated dmf molecules (one with occupancy of 0.36), two coordinated water molecules (one with occupancy 0.64). Compound 1 is the largest coordination cluster containing NiII and CaII ions reported to date. The magnetic properties of 1 show the presence of predominant antiferromagnetic interactions. The magnetic susceptibility and isothermal magnetization data can be well reproduced with: g = 2.145(1), J1 = 2.93(4) cm−1, J2 = −0.41(2) cm−1 and J3 = −5.66(4) cm−1. [ABSTRACT FROM AUTHOR]

A new series of three spin crossover (SCO) Fe(II) complexes based on a cyanocarbanion and on the neutral quinolin-8-amine (aqin) ligands, [Fe(aqin)2(tcnsme)2] (1), [Fe(aqin)2(tcnset)2] (2), and [Fe(aqin)2(tcnspr)2] (3), has been studied. The three complexes display similar molecular structures consisting of discrete [Fe(aqin)2(tcnsR)2] complexes [R = Me (1), Et (2), and Pr (3)]. Infrared spectroscopy and magnetic studies, performed on the three complexes, revealed the presence of similar SCO behaviors which strongly differ by their transition temperatures [234 K (1) < 266 K (2) < 360 K (3)]. The increase of the transition temperatures when passing from 1 to 3 may be explained by electronic and packing effects. Thus, when passing from Me (1) to Et (2) and Pr (3), the electron donor effect increases, resulting in an increase of the ligand field and, accordingly, in an increase of the transition temperature. On the other side, examination of the different coordination modes of the cyanocarbanions in the three complexes clearly reveals the crucial role of these coordination modes on the crystal packing and, therefore, on the transition temperature. We can, therefore, attribute the important increase of the transition temperature from complexes 1 to 3 to both effects: the electron donor character of the alkyl groups and the packing effects of the versatile cycnocarbanion ligands. [ABSTRACT FROM AUTHOR]

Thiele (Th) and tetrabenzo-Chichibabin (TBC) derivatives with terminal dibenzocycloheptatriene (DBHept) units were prepared. A clear correlation between their electronic and molecular structures was stablished. Insights into their closed- or open-shell ground states were gained, where particular contribution of the heptagonal carbocycles as end-groups was proved. Remarkably, a thermally accessible triplet diradical configuration was confirmed for the DBHept-TBC compound. [ABSTRACT FROM AUTHOR]

Electron precise [Mo3(μ3-S)(μ-S)3(diphos)3Br3]Br (diphos = dppe, dmpe) incomplete cuboidal clusters with six cluster skeletal electrons (CSE) were converted into paramagnetic cuboidal [Mo3(GaBr)(μ3-S)4(diphos)3Br3] clusters by treatment with elemental Ga. The new heterobimetallic complexes with nine CSE possess a doublet ground state with the unpaired electron density delocalized over the three molybdenum atoms. [ABSTRACT FROM AUTHOR]

The direct reaction between copper nitrate, thymine-1-acetic acid, and 4,4′-bipyridine in water leads to the formation of a blue colloid comprising uniform crystalline nanoribbons (length >1 μm; width ca. 150-185 nm; diameter ca. 15-60 nm) of a coordination polymer. The polymer displays a thymine-based structure freely available for supramolecular interactions. These nanostructures show significant selective interaction with single-stranded oligonucleotides based on adenine. Remarkably, they present low cell toxicity in three cell lines-despite the copper(II) content-and can be used as nanocarriers of oligonucleotides. These results suggest the potential of these types of nanostructures in several biological applications. [ABSTRACT FROM AUTHOR]

Reaction of Fe3(CO)12 with 1,2-dithiolene HSC6H2Cl2SH affords a mixture of complexes [Fe2(CO)6(µ-SC6H2Cl2S)] 1, [Fe2(SC6H2Cl2S)4] 2 and [Fe3(CO)7(µ3-SC6H2Cl2S)2] 3. In the course of the reaction the trimetallic cluster 3 is first formed and then converted into the known dinuclear compound 1 to afford finally the neutral diiron tetrakis(dithiolato) derivative 2. Compounds 2 and 3 have been studied by Mössbauer spectroscopy, X-ray crystallography and theoretical calculations. In compound 2 the metal atoms are in an intermediate-spin FeIII state (SFe = 3/2) and each metal is bonded to a bridging dithiolene ligand and a non-bridging thienyl radical (S = 1/2). Magnetic measurements show a strong antiferromagnetic coupling in complex 2. Cyclic voltammetry experiments show that the mixed valence trinuclear cluster 3 undergoes a fully reversible one electron reduction. Additionally, compound 3 behaves as an electrocatalyst in the reduction process of protons to hydrogen. [ABSTRACT FROM AUTHOR]

The synthesis and crystal structures of five radical cation salts based on the organic donors bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF), racemic ethylenedithio-methyl-oxazoline-tetrathiafulvalene (EDT-TTF-MeOx) and the enantiopure (S,S,S,S) and (R,R,R,R) tetramethyl-bis(ethylenedithio)tetrathiafulvalene (TMBEDT-TTF) and the D3-symmetric anion tris(tetrachlorobenzenediolato)phosphate(V) (TRISPHAT) are reported. The salts are formulated as [BEDT-TTF][(rac)-TRISPHAT]·CH2Cl2(1), [BEDT-TTF][(rac)-TRISPHAT]·2CH3CN (2), [(rac)-EDT-TTF-Ox][(rac)-TRISPHAT]·CH3CN (3), [(S,S,S,S)-TMBEDT-TTF][(rac)-TRISPHAT]·2CH3CN (4), and [(R,R,R,R)-TMBEDT-TTF][(rac)-TRISPHAT]·2CH3CN (5). The donors are fully oxidized and self-assemble in dyads inserted in the channels generated by the packing of the TRISPHAT anions. Magnetic and EPR measurements performed on compounds 1and 2clearly indicate weak interactions within the dimers in compound 1, characterized by a very narrow line in the EPR spectrum, while the radicals are strongly coupled in compound 2. [ABSTRACT FROM AUTHOR]

A new polymeric approach, based on cyanocarbanion ligands, for the design of spin crossover (SCO) compounds led us to the compound [Fe(abpt)2(tcpd)] (1) (tcpd2- = (C[C(CN)2]3)2-, abpt = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole) which has been characterised as the first SCO molecular chain involving a cyanocarbanion as bridging ligand. [ABSTRACT FROM AUTHOR]

Abstract: A new two-dimensional (2D) thiocyanato-bridged cobalt(II) network formulated as [LCo2(NCS)2] n (1), has been synthesized with the Schiff base ligand N,N′-bis(3-methoxysalicylidenimino)-1,3-diaminopropane (H2L) and thiocyanate anions. This novel layered compound has been completely characterized by elemental analysis, FT-IR, UV–Vis spectroscopy and the structure has been established by single crystal X-ray diffraction studies. The structure of 1 consists of a doubly phenoxo-bridged dimer comprising two different cobalt(II) centers with different coordination geometries (octahedral and tetrahedral). The 2D network is accomplished by bridging thiocyanate ligands, connecting the dimeric motifs in an end-to-end fashion. Variable-temperature magnetic susceptibility and EPR measurements reveal predominant antiferromagnetic exchange interaction in the complex. [ABSTRACT FROM AUTHOR]

A new tridentate N2O donor Schiff base ligand [(C6H5C(OH)CHC(CH3)NCH2C5H4N)LH] was obtained by 1:1 condensation of benzoylacetone with 2-picolylamine and has been used to synthesise a mononuclear [CuLCl] (1) and an end-to-end dicyanamide bridged polynuclear {[Cu2(μ-L)2(μ2-1,5-(CN)2N)]ClO4}n (2) copper(II) complexes. The ligand, 1 and 2 were clearly characterised by elemental analysis, FT-IR, 1H NMR, UV–Vis spectral studies, electrochemical studies and in addition single crystal X-ray diffraction studies were performed for 1 and 2. The Schiff base ligand [LH] shows a significant variation in its coordination behaviour with copper(II) ion in absence and in presence of dicyanamide ion in 1 and 2 respectively. In absence of dicyanamide the deprotonated enolato oxygen of the tridentate Schiff base ligand [L]− coordinates the copper(II) ion in a monodentate fashion generating a mononuclear species (1) whereas in presence of the dicyanamide ion, the deprotonated enolato oxygen of [L]− bridges two adjacent [CuL(CN)2N] units through μ-OL bridges, forming dimers. The dimeric units are further linked to adjacent dimeric units through μ2-1,5-dicyanamide bridges to produce 1D polymeric chains in 2. Variable temperature magnetic susceptibility measurements for 2 in the temperature range 2-300 K reveal the presence of weak antiferromagnetic exchange interactions in the polymeric chain. [Copyright &y& Elsevier]

The electron precise [Mo 3 (μ 3 -Se)(μ-Se) 3 (dppe) 3 Br 3 ] + incomplete cuboidal complex, with six cluster skeletal electrons (CSE), was converted into the paramagnetic bicapped [Mo 3 (μ 3 -Se) 2 (μ-Se) 3 (dppe) 3 ] + cluster ( 1 + ), with an unusual seven metal electron population, by treatment with elemental Ga. The cluster core consists of an almost equilateral Mo 3 triangle (Mo–Mo distances are in the range 2.7583(7)–2.7748(7) Å with an average value of 2.77(3) Å), capped by two selenide ligands. The remaining selenium atoms bridge adjacent metal atoms, defining a virtually planar Mo 3 (μ-Se) 3 unit, with the capping Se atoms positioned above and below this plane. The new complex possesses a doublet ground state with the unpaired electron density delocalized over the three metal atoms. DFT calculations show that the HOMO has “a 1 ” symmetry, precluding any Jahn–Teller distortion on the cluster core and giving support to EPR and structural observations. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of compound [Rh2(O2CEt)4(H2O)2] (1) and one-dimensional heterobimetallic polymers Kn{Rh2(O2CEt)4[Au(CN)2]}n (2) and Kn{Rh2(O2CMe)4[Au(CN)2]}n·4nH2O (3), constructed from dirhodiumtetracarboxylato units, [Rh2(O2CR)4]+, and dicyanoaurate, [Au(CN)2]-, fragments are described. In both compounds 2 and 3 the resulting polymeric chains are nonlinear and have in common similar structural parameters, although the solid state supramolecular arrangement is very different. These structural differences explain the fact that complex 2 displays aurophilic interactions while this type of interactions are absent in complex 3. As a result, compound 2 shows rich blue luminescent properties whereas compound 3 is not luminescent. The electrical conductivity in solid state of compounds 2 and 3 is also studied. [ABSTRACT FROM AUTHOR]

Abstract: A tridentate NNO donor Schiff base ligand [(1Z,3E)-3-((pyridin-2-yl)methylimino)-1-phenylbut-1-en-1-ol= LH] in presence of azide ions coordinates with cobalt(II) and copper(II) ions giving rise to three new coordination complexes [Co2(L)2(μ1,1-N3)2(N3)2] (1), [Cu2(L)2(μ1,3-N3)]·ClO4 (2) and [(μ1,1-N3)2Cu5(μ-OL)2(μ1,1-N3)4(μ1,1,1-N3)2] n (3). The complexes have been characterized by elemental analysis, FT-IR, UV–Vis spectral studies, and single crystal X-ray diffraction studies. These complexes demonstrate that under different synthetic conditions the azide ions and the Schiff base ligand (LH) show different coordination modes with cobalt(II) and copper(II) ions, giving rise to unusual dinuclear and polynuclear species (1, 2 and 3) whose structural variations are discussed. Magneto-structural correlation for the very rare singly μ1,3-N3 bridged CuII–Schiff base dinuclear species (2) has been studied. In addition, the catalytic properties of 1 for alkene oxidation and the general catalase-like activity behavior of 2 have been discussed. [Copyright &y& Elsevier]

Abstract: This review focuses on new families of spin crossover (SCO) complexes based on polynitrile anions as new anionic ligands or on polyazamacrocycles as neutral macrocyclic ligands. We have shown that the structural and electronic characteristics (original coordination modes and high electronic delocalization) of the polynitrile anions can be tuned by slight chemical modifications such as substitution of functional groups or variation of the negative charge to design new discrete or polymeric SCO systems. In our ongoing work on the design of new molecular systems based on new ligands that can be fine-tuned via chemical modifications, another promising way which has been recently developed in our group concerns the use of new neutral polydentate ligands which are able to tune the ligand field energy around the metal centre. Here we report some recent original Fe(II) SCO complexes based on such polydentate ligands. [Copyright &y& Elsevier]

Abstract: Two new copper(II) complexes, [Cu3(L1)2(H2O)2](ClO4)2 (1) and [CuL2 (H2O)] (2) have been derived from two di-compartmental Schiff base ligands H2L1 and H2L2 , respectively. Depending on slight modification of the substituent group of the potentially N2O4 donor ligands, tri- and mononuclear structures are obtained, which have been confirmed by single-crystal X-ray diffraction studies. Both complexes have been characterized by elemental analysis, IR, UV–vis and EPR spectroscopy. Complex 1 consists of an angular trinuclear array of copper ions, while complex 2 consists of a mononuclear copper center. Variable temperature magnetic susceptibility measurements have been performed to investigate the magnetic behaviour of complex 1 and the result indicates a strong antiferromagnetic exchange interaction (J =−120.1(2)cm−1) between the adjacent copper(II) centers through two double μ2-phenoxo bridges. Complex 2 is a mononuclear inclusion compound encapsulating one water molecule in the vacant external compartment of the ligand through hydrogen-bonding interactions. [Copyright &y& Elsevier]

Abstract: Four novel heterometallic complexes [Co2Cr2(NCS)4(HDea)2(Dea)2]·4dmf (1), [Co2Cr2(NCS)4(HDea)2(Dea)2]·4dmso (2), [Mn2Cr2(NCS)4(HDea)2(Dea)2(dmf)2]·2dmf (3) and [Mn2Cr2(NCS)4(HDea)2(Dea)2(dmso)2]·4dmso (4) have been prepared using zerovalent cobalt (1, 2) or manganese (3, 4), Reineckes salt, ammonium thiocyanate and a non-aqueous solution of diethanolamine (H2Dea) in air. The single X-ray analysis reveals that all compounds have similar centrosymmetric crystal structures based on a tetranuclear {M2Cr2(μ3-O)2(μ-O)4} (M=Co, Mn) core. Variable-temperature magnetic susceptibility measurements of 1, 2 and 4 show antiferromagnetic coupling between the magnetic centers, while 3 exhibits a ferromagnetic behavior. [Copyright &y& Elsevier]

New iron(Il) complexes of formulas [Fe(abpt)2(tcm)2} (1), [Fe(abpt)2(tcnome)2] (2), and [Fe(abpt)2(tcnoet)2] (3) (abpt = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole, tcm- = [C(CN)3]- = tricyanomethanide anion; tcnome = [(NC)2CC(OCH3)C(CN)2]- = 1,1 ,3,3-tetracyano-2-methoxypropenide anion; tcnoet- = [(NC)2CC(OC2H5)C(CN)2]- 1,1 ,3,3-tetracyano-2-methoxypropenide anion) have been synthesized and characterized by infrared spectroscopy, magnetic properties and by variable-temperature single-crystal X-ray diffraction. The crystal structure determinations of 1 and 2 reveal in both cases centrosymmetric discrete iron(ll) monomeric structures in which two abpt chelating ligands stand in the equatorial plane and two terminal polynitrile ligands complete the distorted octahedral environment in trans positions. For 3, the crystallographic studies revealed two polymorphs, 3-A and 3-B, exhibiting similar discrete molecular structures to those found for 1 and 2 but with different molecular arrangements. In agreement with the variable-temperature single-crystal X-ray diffraction, the magnetic susceptibility measurements, performed in the temperature range 2-400 K, showed a spin-crossover phenomenon above room temperature for complexes 1, 3-A, and 3-B with a T½ of 336, 377, and 383 K, respectively, while complex 2 remains in the high-spin ground state (S = 2) in the whole temperature range. To understand further the magnetic behaviors of 1, 3-A, and 3-B, single-crystal X-ray diffraction measurements were performed at high temperatures. The crystal structures of both polymorphs could not be obtained above 400 K because the crystals decomposed. However, single-crystal X-ray data have been collected for compound 1, which reaches the full high-spin state at lower temperatures. Its crystal structure, solved at 400 K, showed a strong modification of the iron coordination sphere (average Fe-N = 2.157(3) A vs 1.986(3) A at 293 K). In agreement with the magnetic properties. Such structural behavior is a signature of the spin-state transition from low-spin (LS) to high-spin (HS). On the basis of the intermolecular π stacking observed for the series described in this paper and for related complexes involving similar discrete structures, we have shown that complexes displaying frontal π stacking present spin transition such as 1, 3-A, and 3-B and those involving sideways π stacking such as complex 2 remain in the HS state. [ABSTRACT FROM AUTHOR]

The paramagnetic and chiral anion [Fe(C5O5)3]3- (C5O52- = croconate) has been combined with the organic donor BEDT-TTF (=ET = bis(ethylenedithio)tetrathiafulvalene) to synthesize a novel paramagnetic semiconductor with the first chirality-induced α phase, α-(BEDT-TTF)5[Fe(C5O5)3]·5H2O (1), and one of the few known paramagnetic molecular metals, β-(BEDT-TTF)5[Fe(C5O5)3]·C5H5CN (2). Both compounds present layers of BEDT-TTF molecules, with the α or β packing modes, alternating with layers containing the high-spin S = 5/2 Fe(III) anions and solvent molecules. In the a phase, the alternation of the chiral [Fe(C5O5)3]3 anions along the direction perpendicular to the BEDT-TTF chains induces an alternation of the tilt angle of the BEDT-TTF molecules, giving rise to the observed a phase. The a phase presents a semiconductor behavior with a high room-temperature conductivity (6 S·cm-1) and an activation energy of 116 meV. The β phase presents a metallic behavior down to Ca. 120 K, where a charge localization takes place with a reentrance to the metallic state below ca. 20 K followed by a metal-semiconductor transition at ca. 10 K. The magnetic properties are dominated by the paramagnetic S = 5/2 [Fe(C5O5)3]3- anion with an extra Pauli-type paramagnetism in the metallic β phase. The ESR spectra confirm the presence of the high-spin Fe(III)-containing anion and show a progressive localization in the organic sublattice along with an antiferromagnetic coupling below ca. 120 K that, in the metallic β phase, could be at the origin of the transition from the metallic to the activated conductivity regime. The correlation between crystal structure and conductivity behavior has been studied by means of tight-binding band structure calculations which provide a rationalization of the charge distribution and conductivity results. [ABSTRACT FROM AUTHOR]

An original magnetic bistability and a thermochromic transition are observed in a new CuII molecular chain. Thermal structural studies reveal changes in the CuII coordination sphere, driven by a more pronounced Jahn—Teller effect at low temperature. These distortions provoke a gradual color change. The structural study at 10 K shows a dimerization of the molecular chain, in agreement with the abrupt magnetic transition observed at 30 K. [ABSTRACT FROM AUTHOR]