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Conformational analysis of the three geometrical isomers of (aqua)(ethylenediamine-tripropionato)chromium(III) has been performed with the Consistent Force Field (CFF) program. Four stable conformations were identified for trans(H2O,O) and trans(H2O,NH), and five stable conformations for trans(H2O,N′) geometrical isomer. Their structure and relative strain were analyzed and compared with the available experimental data. The conformer representing the global minimum (population 58% at 298 K) was found to match closely the X-ray structure of the trans(H2O,NH) isomer. The factors which determine the individual chelate ring conformations, and conformational transmission through the entire ligand system was elucidated, and a possible extension of this analysis to other EDTA-type complexes is indicated. [Copyright &y& Elsevier]

Novel cobalt(III) complexes containing three kinds of assembled ligands, L1&z.sbnd;L2=dapymt–tbba(2-), tbba–dapymt(1-) and apymt–tbba(1-) (H3tbba=thiobarbituric acid; Hdapymt=4,6-diamino-2-thiouracil; Hapymt=4-amino-2-thiouracil), were prepared from the mixed ligand systems, where L2 indicates the coordinated ligand to the Co(III) ion and L1 is a pendant ligand bonded to L2. These complexes were characterized by UV–Vis absorption spectra and NMR spectroscopy. The crystal structures of [Co(Htbba)(en)2]ClO4·2H2O (2) (en=ethane-1,2-diamine), [Co{dapymt–tbba(2-)}(en)2]ClO4·3H2O (3) and [Co{apymt–tbba(1-)}(en)2](ClO4)Cl·3H2O (5′) revealed that coordination occurs through the S(1) and N(1) donors of tbba and the latter complexes 3 and 5′ have an assembled ligand; a new bond is formed between the C(5) atom of tbba and the S(2) atom of dapymt or apymt. An intramolecular hydrogen bond between O(1) of tbba and NH of en was found in all crystals. An interesting intermolecular π–π stacking interaction was found in 5′. [Copyright &y& Elsevier]

Examines the hydrogen molecular assembly from polyoxovanadate and tetramethylbiimidazole. Characteristics of decavanadate anion; X-ray crystal structure of the hydrogen compound; Crystallographic inversion center on the decavanadate anion.

The article focuses on the crystallization of the compound fac-triaqua[tris(2-pyridyl)amine-κ3N]chromium(III) tris (trifluoromethanesulfonate). In the crystal structure chromium ion is coordinated by the symmetry-related nitrogen atoms of tris(2-pyridyl)amine, which acts as a tripodal ligand. A threefold rotation axis passes through the chromium and amine nitrogen atoms. In the experiment red crystals of the compound are formed.

In the title compound, cis-[CrF2(C10H8N2)2]ClO4, the CrIII ion is coordinated by the four N atoms [Cr—N = 2.0480 (14)–2.0842 (14) Å] from two 2,2′-bipyridine ligands and two F− ions [Cr—F = 1.8409 (10) and 1.8541 (10) Å] in a distorted octa­hedral arrangement. The crystal packing is stabilized by π–π inter­actions and weak inter­molecular C—H⋯F and C—H⋯O hydrogen bonds. [ABSTRACT FROM AUTHOR]

A novel luminescent clamshell-like platinum(II) complex with rac-tartrate, rac-[{Pt II ( 4 Me 2 bpy)} 2 (μ-tart)] (Pt 2 ; 4 Me 2 bpy: 4,4'-dimethyl-2,2'-bipyridine; tartH 2 2- : tartrate), was synthesized, and its vapo-, thermo-, and solvatochromic behavior was studied. The complex was isolated in four crystal forms, namely, Pt 2 ·4H 2 O (color under ambient light: yellow, λ em = 573 nm, intramolecular Pt···Pt separation: 3.55 Å), Pt 2 ·4MeOH (red, 650 nm, 3.33 Å), anhydrate Pt 2 (red, no luminescence, 3.70 Å), and Pt 2 ·2H 2 O (orange, 595 nm, 3.60 Å). Vapo- and heat-responsive crystal-to-crystal phase transitions were observed by time- and/or temperature-dependent powder X-ray diffraction, and the molecular and crystal structures of the above crystal forms were determined by either single-crystal X-ray crystallography or Rietveld refinement of powder X-ray diffraction. Vapor diffusion of MeOH to Pt 2 ·4H 2 O induced a reversible phase transition to Pt 2 ·4MeOH. This structural transformation significantly changed the intramolecular Pt-Pt interactions, affecting the absorption and emission colors. Accordingly, the luminescence chromism originates from alternation of the luminescent nature between a triplet metal-ligand-to-ligand charge-transfer state ( 3 (ML tart )L bpy CT) of Pt 2 ·4H 2 O and a triplet metal-metal-to-ligand charge-transfer state ( 3 MML bpy CT) of Pt 2 ·4MeOH. Heating Pt 2 ·4H 2 O induced a phase transition to anhydrate Pt 2 , and under atmospheric conditions, anhydrate Pt 2 transformed spontaneously to Pt 2 ·2H 2 O. Vapor diffusion of H 2 O to Pt 2 ·2H 2 O caused reconstruction of Pt 2 ·4H 2 O. The thermochromism originates from changes in the intermolecular interactions between stacked complexes. The solvatochromism was evaluated using the Kamlet-Taft solvatochromic equation, the acceptor number, and the E T (30) scale for the solvent, and the hydrogen-bond acidity of the solvent contributed significantly to the solvent-dependent absorption properties.

In the neutral complex mol-ecule of the title compound, fac-[CrCl3(tpa)] [tpa is tris-(pyridin-2-yl)amine; C15H12N4], the Cr(III) ion is bonded to three N atoms that are constrained to a facial arrangement by the tpa ligand and by three chloride ligands, leading to a distorted octa-hedral coordination sphere. The average Cr-N and Cr-Cl bond lengths are 2.086 (5) and 2.296 (4) Å, respectively. The complex mol-ecule is located on a mirror plane. In the crystal, a combination of C-H⋯N and C-H⋯Cl hydrogen-bonding inter-actions connect the mol-ecules into a three-dimensional network.

For Δ-SAPR-8-Cs[Ln((+)-hfbc)4]((+)-hfbc = (+)-heptafluoro-butyrylcamphorate; Cs-Ln), the vibrational circular dichroism pattern and intensity of Cs-La, Cs-Nd, Cs-Gd, Cs-Ho, Cs-Er, Cs-Lu and Cs-Sm, Cs-Eu, Cs-Tb, Cs-Dy, Cs-Tm, Cs-Yb, respectively, are correlated with the even and the odd parity of total orbital angular momentum in the ground state terms.

For electronic circular dichroism in the 4f-4f transitions (4f-4f CD) of a series of nine tetrakis ((+)-3-heptafluorobutyrylcamphorato) Ln(III) complexes, Δ-SAPR-8-C(4)(llll) Cs[Ln((+)-hfbc)(4)]·H(2)O (Cs-Ln = Cs-Pr, -Nd, -Sm, -Eu, -Dy, -Ho, -Er, -Tm, -Yb), the spectroscopic observables such as the dissymmetry factor g = Δε/ε values with the intensities (Δε) of the CD components and the molar absorption intensities (ε) in the 4f-4f transitions between the (2S+1)L(J) levels are compared with each other to test the classification of the CD components in the relative order of the observables predicted in terms of the selection rule for 4f-4f transitions. The 4f-4f CD-based chiroptical spectra-structural relationship across the series of Δ-SAPR-8-C(4)(llll) lanthanide(III) complexes is proposed: the signs of the 4f-4f CD or CPL in the hypersensitive transitions are related to the absolute configuration; Ln complexes with a negative CD component have the Δ-configuration around Ln(III) and vice versa.

A comprehensive study of the magnetic and photomagnetic behaviors of cis-[Fe(picen)(NCS)(2) ] (picen = N,N'-bis(2-pyridylmethyl)1,2-ethanediamine) was carried out. The spin-equilibration was extremely slow in the vicinity of the thermal spin-transition. When the cooling speed was slower than 0.1 K  min(-1), this complex was characterized by an abrupt thermal spin-transition at about 70 K. Measurement of the kinetics in the range 60-70 K was performed to approach the quasi-static hysteresis loop. At low temperatures, the metastable HS state was quenched by a rapid freezing process and the critical T(TIESST) temperature, which was associated with the thermally induced excited spin-state-trapping (TIESST) effect, was measured. At 10 K, this complex also exhibited the well-known light-induced excited spin-state-trapping (LIESST) effect and the T(LIESST) temperature was determined. The kinetics of the metastable HS states, which were generated from the freezing effect and from the light-induced excitation, was studied. Single-crystal X-ray diffraction as a function of speed-cooling and light conditions at 30 K revealed the mechanism of the spin-crossover in this complex as well as some direct relationships between its structural properties and its spin state. This spin-crossover (SCO) material represents a fascinating example in which the metastability of the HS state is in close vicinity to the thermal spin-transition region. Moreover, it is a beautiful example of a complex in which the metastable HS states can be generated, and then compared, either by the freezing effect or by the LIESST effect., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A novel topologically frustrated pentanuclear cluster helicate [{Cu(II)(μ-L)(3)}(2)Cu(II) (3)(μ(3)-OH)](3+) (L(-)=3,5-bis(2-pyridyl)pyrazolate) has been synthesized and characterized. This cluster has a helical arrangement of ligands around the central metal core. Dzyaloshinsky-Moriya interactions are essential components to observe a gradual magnetization and forbidden transitions of high-field/multi-frequency (HF/MF)-ESR. The origin of the magnetic anisotropy of this compound is influenced by its helical spin structure, and consequently, the Cu(5)-cluster helicate introduces a unique magnetic anisotropy. This observation is a direct evidence of the topological part of the new spin phase in a magnetic system.

Spin crossover: The photomagnetic properties of a series of [{Fe(NCS)(py-X)}(2)(bpypz)(2)] (NCS=thiocyanate, py=pyridine, X=4-Mepy, py, 3-Mepy, 3-Clpy and 3-Brpy, and bpypz=3,5-bis(pyridine-2-yl)pyazolate) binuclear complexes are close to the antiferromagnetic response of [{Fe(NCS)(3,5-dmpy)}(3)(bpypz)(2)] (3,5-dmpy=3,5-dimethylpyrazine), which is characterised by two iron(II) metal ions in a high-spin (HS) electronic configuration (see figure).This paper describes the photomagnetic properties of a series of binuclear iron(II) complexes belonging to the [{Fe(NCS)(py-X)}(2)(bpypz)(2)] family (NCS=thiocyanate; py=pyridine; bpypz=3,5-bis(pyridine-2-yl)pyrazolate; and py-X=4-Mepy (1), py (3), 3-Mepy (4), 3-Clpy (5), and 3-Brpy (6)). All of these complexes display a complete thermal spin transition centred between 100 and 150 K, and undergo the light-induced excited-spin-state trapping (LIESST) effect at low temperatures. The T(LIESST) relaxation temperature of the photoinduced high-spin state for each compound has been determined. For all of the complexes, it has been found that the T(LIESST) curves at low temperature are close to the antiferromagnetic response of the [{Fe(NCS)(3,5-dmpy)}(2)(bpypz)(2)] (3,5-dmpy=3,5-dimethylpyridine) (7) complex that is characterised by two iron(II) metal ions in a HS electronic configuration, giving some evidence of a quantitative low spin-low spin-->high spin-high spin (LS-LS-->HS-HS) photoconversion process. Depending on the nature of the cooperativity, the kinetics have been treated with stretched exponential, simply exponential, or sigmoidal models. Interestingly, this series of dinuclear complexes follows a previously proposed linear relationship between the T(LIESST) and their thermal spin transition temperatures T(1/2): T(LIESST)=T(0)-0.3T(1/2). T(0) for these compounds is equal to 100 K. Based on this, and by using the empirical linear relationship found between the thermal spin transition and the Hammett constant, the HS-HS properties of complex 7 have been understood as a reflection of the physical impossibility that the T(LIESST) was higher than T(1/2). The close vicinity of the thermal spin-crossover phenomenon of 7 has been successfully checked by applying hydrostatic pressure.

The largest CPL activity ever measured was observed for cesium tetrakis(3-heptafluoro-butylryl-(+)-camphorato) Eu(III) complexes in EtOH and CHCl3 solutions substantiating the stereospecific formation of chiral Delta-SAPR-(C4) configuration with the aid of Cs+...FC (fluorocarbon) interactions more clearly than the exciton CD spectra.

For newly prepared sodium tetrakis(3-heptafluorobutylryl-(+)-camphorato) Ln(III) complexes, the X-ray crystal analysis revealed an unprecedented pseudo-achiral dodecahedron (DD-8 (D(2d))), whereas in CHCl3 solution, the exciton CD and 19F NMR spectra showed a novel chiral Delta-SAPR-8 (C4) configuration which is stereospecifically formed by a trapped Na+ ion with Na+...FC (fluorocarbon) interactions.

The variable temperature magnetic susceptibility, X-ray crystallography, and Mössbauer and Raman spectra of a new dinuclear complex-based one-dimensional coordination polymer [[Fe(II)2(NCS)2(mu-bpypz)2](micro-4,4'-bpy)].MeOH demonstrated a steep one-step [HS-HS] to [LS-LS] spin transition.

Photolysis of the (azido)(pyridine-2-thiolato)iridium(III) complex CpIr(2-Spy)(N3) (1) gave a pyridine-1-imido-2-thiolato complex, CpIr(1-N-2-Spy) (2), in which one of the nitrogen atoms of the azide ligand has been inserted into the Ir-N(py) bond (Cp = eta5-C5Me5). Complex 2 reacted quantitatively with methyl iodide to give the N-methylated product, [CpIr(1-NMe-2-Spy)]I (3). X-ray crystallography revealed that both 2 and 3 have similar two-legged piano stool structures with planar 1-N-2-Spy2- or 1-NMe-2-Spy- ligands, which form iridacyclopentadienyl-like rings by moderate S(ppi)/N(ppi) to Ir(dpi) pi donation.

Two series of pyrazolato bridged dinuclear NCS and NCBH3 diiron(II) complexes with various types of 3- or 4-substituted pyridines, [{Fe(NCS or NCBH3)(X-py)}2(mu-bpypz)2], were prepared and their variable-temperature magnetic susceptibilities were measured. There were found linear correlations of the spin-crossover temperatures Tc not only between the NCS and NCBH3 complexes with the corresponding substituted pyridines, but also between the Tc and the Hammett constants, supporting the electronic substituent effect of the coordinated pyridine rather than a steric effect. The ligand field and the interelectronic repulsion parameters together with the thermodynamic data and/or cooperativity factor were discussed in relation with their spin-crossover behavior.

In acidic aqueous solution, a cobalt(III) complex containing monodentate N(9)-bound adeninate (ade(-)), cis-[Co(ade-kappaN(9))Cl(en)(2)]Cl (cis-[1]Cl), underwent protonation to the adeninate moiety without geometrical isomerization or decomposition of the Co(III) coordination sphere, and complexes of cis-[CoCl(Hade)(en)(2)]Cl(2) (cis-[2]Cl(2)) and cis-[Co(H(2)ade)Cl(en)(2)]Cl(3) (cis-[3]Cl(3)) could be isolated. The pK(a) values of the Hade and H(2)ade(+) complexes are 6.03(1) and 2.53(12), respectively, at 20 degrees C in 0.1 M aqueous NaCl. The single-crystal X-ray analyses of cis-[2]Cl(2).0.5H(2)O and cis-[3]Cl(2)(BF(4)).H(2)O revealed that protonation took place first at the adeninate N(7) and then at the N(1) atoms to form adenine tautomer (7H-Hade-kappaN(9)) and cationic adeninium (1H,7H-H(2)ade(+)-kappaN(9)) complexes, respectively. On the other hand, addition of NaOH to an aqueous solution of cis-[1]Cl afforded a mixture of geometrical isomers of the hydroxo-adeninato complex, cis- and trans-[Co(ade-kappaN(9))(OH)(en)(2)](+). The trans-isomer of chloro-adeninato complex trans-[Co(ade-kappaN(9))Cl(en)(2)]BF(4) (trans-[1]BF(4)) was synthesized by a reaction of cis-[2](BF(4))(2) and sodium methoxide in methanol. This isomer in acidic aqueous solution was also stable toward isomerization, affording the corresponding adenine tautomer and adeninium complexes (pK(a) = 5.21(1) and 2.48(9), respectively, at 20 degrees C in 0.1 M aqueous NaCl). The protonated product of trans-[Co(7H-Hade-kappaN(9))Cl(en)(2)](BF(4))(2).H(2)O (trans-[2](BF(4))(2).H(2)O) could also be characterized by X-ray analysis. Furthermore, the hydrogen-bonding interactions of the adeninate/adenine tautomer complexes cis-[1]BF(4), cis-[2](BF(4))(2), and trans-[2](BF(4))(2) with 1-cyclohexyluracil in acetonitrile-d(3) were investigated by (1)H NMR spectroscopy. The crystal structure of trans-[Co(ade)(H(2)O)(en)(2)]HPO(4).3H(2)O, which was obtained by a reaction of trans-[Co(ade)(OH)(en)(2)]BF(4) and NaH(2)PO(4), was also determined.

Novel metal-complex assemblies constructed from the flexible hinge-like ligand H(2)bhnq (H(2)bhnq=2,2'-bi(3-hydroxy-1,4-naphthoquinone)) have been synthesized. The X-ray crystal structures of these compounds reveal that four types of architectures are accessible by variation of the metal ions. In copper(II) compounds 1-3, the chelating bhnq(2-) ions bridge copper(II) centers to form one-dimensional zigzag chains. The chains of 1-3 are arranged by hydrogen-bonding interactions and stacking interactions to produce porous structures. Cobalt(II) and zinc(II) compounds 4 and 5 form one-dimensional helical chains. In 4 and 5, the crystal packing induces spontaneous resolution of the helical chains with chiral cavities formed perpendicular to the helices. Nickel(II) compounds 6 and 7 form cyclic tetramers. The fourth architecture, a dimer (compound 8), is obtained by the reaction of zinc(II) and bhnq(2-) in MeOH. In these compounds, changes of the dihedral angles and the metal-coordination mode of the bhnq(2-) ion induce the structural versatility. The assemblies of the zigzag chains of the copper(II) compounds exhibit reversible vapochromic behavior. UV/Vis, powder X-ray diffraction, EPR, and adsorption isotherm measurements indicate that this vapochromic behavior is based on the hinge-like flexibility of the bhnq(2-) ion.

The synthesis and characterization of new spin-crossover pyrazolato bridged dinuclear [(FeII(NCS)(py))2(mu-bpypz)2] and the corresponding cyanotrihydroborato-kappaN complexes are described together with the X-ray crystal analysis of the latter in both the high-spin and low-spin states as well as the variable temperature magnetic susceptibility and/or Mossbauer spectra demonstrating the spin-crossover which exhibits an one-step process, but not a two-step one characteristic of the known bpym bridged dinuclear complexes.

In the title compound, [CrBr(2)(C(5)H(14)N(2))(2)](2)Br(2).HClO(4).6H(2)O, there are two independent Cr(III) complex cations which are conformational isomers of each other. The Cr atoms lie respectively on a center of symmetry and on a mirror plane and have octahedral environments, coordinated by the N atoms of two 2,2-dimethylpropane-1,3-diamine ligands and by two Br atoms in trans positions. The Cr-N and Cr-Br bond lengths are in the ranges 2.078 (3)-2.089 (3) and 2.4495 (9)-2.5017 (9) A, respectively. The crystal structure consists of two Cr(III) complex cations, two Br(-) anions, a (ClO(4))(-) anion and an [H(13)O(6)](+) hydrogen-bonded cluster cation.

The crystal structure of the title compound, (C(2)H(10)N(2))[Cr(C(4)H(9)N(2)O(2))(2)](2)Cl(4) x 2H(2)O, has been determined by single-crystal X-ray diffraction studies at 293 and 100 K. The analyses demonstrated that the crystal consists of ethylenediammonium dications (which lie about inversion centres), bis[N-(2-aminoethyl)glycinato]chromium(III) monocations, Cl(-) anions and hydrate water molecules, in a molecular ratio of 1:2:4:2. The complex cation unit has a slightly distorted octahedrally coordinated Cr atom, with two Cr[bond]O and four Cr[bond]N bonds in the ranges 1.951 (1)-1.953 (1) and 2.054 (1)-2.089 (2) A, respectively, at 293 K. The geometry of the bis[N-(2-aminoethyl)glycinato]chromium(III) moiety was found to be trans,cis,cis with respect to the carboxylate O atom and the primary and secondary amine N atoms. The two analyses, at 293 and 100 K, exhibited no remarkable structural differences, although the colour of the crystals did differ, being red at 293 K and orange at 100 K.

1H or (2)H NMR contact shifts of the beta-diketonate methine in the radical complexes [Ni(beta-diketonato)(2)(NIT2-py)] and [Ni(beta-diketonato)(tmen)(NIT2-py)](+) (NIT2-py = 2-(2'-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-3-oxide-1-oxyl and tmen = N,N,N',N'-tetramethylethylenediamine) were found to correlate to a product of the respective (1)H or (2)H NMR contact shifts of the methine in the nonradical complexes [Ni(beta-diketonato)(2)(tmen)] and the fractional contribution to the Ni(II) moiety arising from the magnetic interaction between nickel(II) ion and NIT2-py radical, proposing a new method to estimate the exchange coupling constant J value from the NMR contact shifts. Variable temperature (2)H NMR measurements of the C-D signals in [Ni(acac-d)(2)(NIT2-py)], [Ni(acac-d)(tmen)(NIT2-py)](+), and [Ni(acac-d)(2)(tmen)] suggested the topological discrimination of the acetylacetonates.

The reaction of Ln(III) ions with a tripodal ligand HBpz(3)(-) (hydrotris(pyrazol-1-yl)borate) and a "complex ligand" [Cr(acac)(2)(ox)](-) (acac(-) = acetylacetonate, ox(2)(-) = oxalate) in aqueous solution afforded a series of the novel 3d-4f heterodinuclear complexes [(acac)(2)Cr(ox)Ln(HBpz(3))(2)] (Ln = Eu (1), Gd (2), Tb (3), Yb (4), Lu (5)). The crystal structure of 4 has been determined by X-ray diffraction. Complex 4 crystallizes in monoclinic space group P2/n, of which the cell parameters are a = 8.594(3) Å, b = 18.538(4) Å, c = 12.093(2) Å, beta = 93.71(2) degrees, and Z = 2. The Yb atom has an eight-coordinate distorted square antiprismatic coordination geometry. The intramolecular Cr.Yb distance is 5.631(1) Å. The magnetic susceptibility data for complex 2 showed that the Cr(III)-Gd(III) interaction is weakly antiferromagnetic with an exchange coupling constant J(CrGd) = -0.09 cm(-)(1). The luminescence measurements demonstrated the energy transfers for both Ln(III) --> Cr(III) and Cr(III) --> Ln(III), of which the degree of emission quenching depends on the energy gap of the excited levels in two metal centers. These results reveal that the metal-metal interactions between Cr(III) and Ln(III) are very weak in magnetic interaction but are strong from the viewpoint of energy transfer.