Transition-metal(II) thiocyanate coordination compounds containing 4-allyl-1,2,4-triazole. Structure and magnetic properties.

The synthesis and characterisation of a series of dinuclear and polynuclear coordination compounds with 4-allyl-1,2,4-triazole are described. Dinuclear compounds were obtained for Mn(II) and Fe(II) with composition [M₂(Altrz)₅(NCS)₄], and for Co(II) and Ni(II) with composition [M₂(Altrz)₄(H₂O)(NCS)₄](H₂O)₂. The crystal structure of [Co₂(Altrz)₄(H₂O)(NCS)₄](H₂O)₂ was solved at room temperature. It crystallizes in the monoclinic space group P2₁/n. The lattice constants are a = 18.033(3) Å, b = 13.611(2) Å, c = 15.619(3) Å, β = 92.04(2)° Z = 4. One cobalt ion has an octahedrally arranged donor set of ligands consisting of three vicinal nitrogens of 1,2-bridging triazoles (CoN = 2.14–2.15 Å), one terminal triazole nitrogen (CoN = 2.12 Å) and two N-bonded NCS anions (CON = 2.08 Å). The other Co(II) ion has the same geometry, but the terminal triazole ligand is replaced by H₂O (CoO = 2.15 Å). The crystal structure is stabilised by hydrogen bonding through H₂O molecules, S-atoms of the NCS anions and the lone-pair electron of the monodentate triazole. The magnetic exchange in the Mn, Co and Ni compounds is antiferromagnetic with J-values of ?0.4 cm^?1, ?10.9 cm^?1 and ?8.7 cm^?1 respectively. The Co compound was interpreted in terms of an Ising model. For [Zn₂(Altrz)₅(NCS)₂]∞[Zn(NCS)₄], [Cu₂(Altrz)₃(NCS)₄]∞ and [Cd₂(Altrz)₃(NCS)₄]∞ chain structures are proposed. In the Cu compound thiocyanates appear to be present, bridging via the nitrogen atom, as deduced from the IR spectrum.     

Spectroscopic and magnetic properties of diethyl (pyridin-4-ylmethyl)phosphate (4-pmOpe) ligand with perchlorate transition metal salts. Crystal structure of [Cu(4-pmOpe)2(ClO4)2]

The perchlorate M(II) (M = Cu, Ni, Co) complexes with the diethyl (pyridin-4-ylmethyl)phosphate (4-pmOpe) ligand of the composition [M(4-pmOpe)₂ (H₂O)₂](ClO₄)₂ (M = Ni, Co) and [Cu(4-pmOpe)₂(ClO₄)₂] were prepared and studied. The ligand contains two donor atoms, i.e. pyridine nitrogen and phosphoryl oxygen atoms. In particular, the crystal structure of [Cu(4-pmOpe)₂(ClO₄)₂] was determined by the X-ray method. Its structure consists of a one-dimensional polymeric chain in which copper(II) ions are N,O-bridged by two 4-pmOpe organic ligands in a trans arrangement. Two perchlorate ions occupy the fifth and the sixth coordination sites. The Cu?Cu distance is 9.180 Å. The crystal packing is determined by the weak intermolecular C-H?O hydrogen contacts. The coordination compounds were identified and characterized by elemental analysis, spectroscopic and magnetic studies. Spectroscopic and magnetic results of the copper(II) compound are presented in the light of the crystal structure. The magnetic data indicate very weak intra- and interchain magnetic exchange interactions (J^’ = −0.43 and zJ^’ = 0.29 cm⁻¹, respectively). The spectroscopic and magnetic properties of the Co(II) and Ni(II) complexes indicate octahedral and polymeric structure of both compounds in which 4-pmOpe ligand also acts as N,O-bridge between metal ions.     

New coordination polymers based on a novel polynitrile ligand: Synthesis,structure and magnetic properties of the series [M(tcnoetOH)2(4,4′-bpy)(H2O)2] (tcnoetOH− = [(NC)2CC(OCH2CH2OH)C(CN)2]−; M = Fe,Co and Ni)

A novel polynitrile anionic ligand, tcnoetOH^?(=[(NC)₂CC(OCH₂CH₂OH)C(CN)₂]^?), has been synthesized by a one-pot reaction from a cyclic acetal and malononitrile. This ligand has been successfully used to prepare, with 4,4′-bpy as co-ligand, a novel series of coordination polymers formulated as [M(tcnoetOH)₂(4,4′-bpy)(H₂O)₂] with M(II) = Fe (1), Co (2) and Ni (3). These isostructural compounds present a linear chain structure consisting of octahedrally coordinated metal ions bridged by trans 4,4′-bpy ligands. The coordination sphere of the metal ions is completed with two terminal tcnoetOH^? ligand and two water molecules. The magnetic properties indicate that the three compounds are paramagnetic, as expected from the long 4,4′-bpy bridge connecting the metal atoms. Their magnetic properties have been fitted with a model of isolated ions including a zero field splitting for the Fe(II) and Ni(II) derivatives.     

Synthesis, crystal structure, hydrogen bonding and spectroscopy of Co, Mn and Ni oxalate complexes with the ligand (N,N′-bis(2-pyridylmethyl)-1,3-propanediamine)

Three new compounds are reported with the tetradentate ligand (N,N′-bis(2-Pyridylmethyl)-1,3-propanediamine) (abbreviated as pypn), two mononuclear compounds i.e. [Co(pypn)(C₂O₄)](ClO₄) (1), [Mn(pypn)(C₂O₄)](ClO₄) (2) and one dinuclear compound [Ni₂(pypn)₂(C₂O₄)](ClO₄)₂(C₂H₆O)_1/4(H₂O) (3). In the Co(III) and Mn(II) complexes the oxalate behaves as bidentate ligand, chelating the metal in the O,O′ mode, whereas in the Ni(II) compound the oxalate behaves as tetradentate ligand binding each Ni(II) ion by two oxygen atoms and bridging the two metallic centers.The synthesis, X-ray crystal structure of all three compounds and their spectroscopic properties are presented in detail. The geometry around the Co³⁺, Mn³⁺, Ni²⁺ ions is essentially octahedrally based, while the stabilization of the crystal lattice in all cases is maintained by interesting hydrogen bond systems.     

Cobalt and nickel complexes of versatile imidazole- and pyrrole-2-carbaldehyde thiosemicarbazones. Synthesis, characterisation and antimicrobial activity

Ni(II), Co(II) and Co(III) complexes of imidazole- and pyrrole-2-carbaldehyde thiosemicarbazone ligands (H₂L¹ and H₂L², respectively) have been prepared. The X-ray crystal structures of [Co(L¹)(HL¹)], [Ni(H₂L¹)₂]Cl₂ · 3.5H₂O and [Ni(HL²)₂] have been solved. The Co(III) ion assumes a slightly distorted octahedral coordination geometry, involving both N₂S binding domain of di- and monoanionic ligand molecules. Whereas in [Ni(HL²)₂] the metal ion is tetracoordinated in a square planar geometry by two pyrrole-2-carbaldehyde thiosemicarbazone molecules acting as NS-donor, the spatial array of non deprotonated H₂L¹ ligand molecules in [Ni(H₂L¹)₂]Cl₂ · 3.5H₂O is equivalent to that found for [Co(L¹)(HL¹)]. The in vitro antimicrobial properties of the ligands and their complexes were tested against representative bacterial and fungal strains in broth culture. The compounds H₂L² and [Co(L²)(HL²)(H₂L²)] · 1.5H₂O exhibit a moderate inhibitory effect on the microbial proliferation and only against some Gram positive bacteria.     

Synthesis, crystal structure and esterification of a novel iron(III) 18-metallacrown-6 complex

The trianionic heptadentate ligand, (Z)-3-(5′-chlorosalicylhydrazinocarbonyl) propenoic acid, has been synthesized and reacted with FeCl₃·6H₂O, to produce the complex [Fe^III₆(C₁₂H₈N₂O₅Cl)₆(H₂O)₄(CH₃OH)₂]·8H₂O·4CH₃OH. In the self-assembly process the ligand was esterified and transferred into (Z)-methyl 3-(5′-chlorosalicylhydrazinocarbonyl) propenoate. In the crystal structure, the neutral Fe(III) complex contain a 18-membered metallacrown ring consisting of six Fe(III) and six trianionic ligands. The 18-membered metallacrown ring is formed by the succession of six structural moieties of the type [Fe(III)-N-N]. Due to the meridional coordination of the ligands to the Fe³⁺ ions, the ligands enforce the stereochemistry of the Fe³⁺ ions as a propeller configuration with alternating Λ/Δ forms. The metallacrown can be treated with SnCl₂ or Zn powder to obtain purified ester.     

Hydrothermal synthesis and crystal structure of [Co(2,5-pydc)(H2O)2]n · nH2O (2,5-pydc = 2,5-pyridinedicarboxylate)

A new cobalt(II) compound, [Co(2,5-pydc)(H₂O)₂]_n · nH₂O (1) has been synthesized hydrothermally and characterized by elemental analysis, infrared spectroscopy, thermogravimetric analysis, and single crystal X-ray diffraction. The crystal structure consists of Co(II) centers linked via 2,5-pydc ligands and water molecules, in which every 2,5-pydc ligand adopts the coordination form in quadridentate –NOOO′ mode. The structure is 2-D networks and neighboring layers are further extended into a 3-D supramolecular architecture through hydrogen-bonding interactions between water molecules and carboxyl oxygen atoms.     

Synthesis, spectroscopy and magnetism of novel metal complexes of 3-aminoflavone (3-af). X-ray crystal structure of 3-af and [Cu(3-af)2(NO3)2]

The synthesis and characterization of four new complexes with the bioactive ligand 3-aminoflavone (3-af) are reported. The complexes of general formula [M(3-af)₂(H₂O)₂](NO₃)₂ · nH₂O], where M = Co(II), Ni(II), and Zn(II), and n = 0, 2, 0, respectively, and [Cu(3-af)₂(NO₃)₂] compound were prepared and studied. In particular, to investigate the binding in detail, the crystal structures of the free ligand (3-af) and [Cu(3-af)₂(NO₃)₂] (1) were determined. The new coordination compounds were identified and characterized by elemental analysis, magnetic measurements, and infrared and ligand-field spectra. The crystal structure of the Cu(II) complex reveals that the ligand acts as a N,O-bidentate chelate ligand forming a five-membered ring with the copper(II) ion. The copper(II) ion is octahedrally surrounded by the two amino nitrogens and two carbonyl oxygens from two chelating organic ligands in trans arrangement. Two molecules of coordinated nitrate anions occupy axial positions. The spectral and magnetic properties are in accordance with the structural data of the copper(II) compound. From X-ray powder-diffraction patterns and IR spectra, the complexes of nickel(II) (2) and cobalt(II) (3) were found to be mutually isomorphous. The results of the spectroscopic studies suggest a mononuclear structure of 2 and 3 complexes. The variable-temperature (1.8-300 K) magnetic susceptibility data of 2 indicate a weak ferromagnetic interaction. The magnetic behavior of complex 3 is characteristic of cobalt(II) systems with an important orbital contribution via spin-orbit-coupling and also suggests a weak ferromagnetic interaction.     

Dioxouranium(VI) complexes with 2,6-acetylpyridinebenzoylhydrazones and -semicarbazones

Benzoylhydrazones and semicarbazones derived from 2,6-diacetylpyridine react with common dioxouranium(VI) compounds such as uranyl nitrate or [NBu₄]₂[UO₂Cl₄] to form air-stable complexes. 2,6-Diacetylpyridinebis(benzoylhydrazone) (H₂L¹), 2,6-diacetylpyridinebis(N4-phenylsemicarbazone) (H₂L²) and the asymmetric proligand 2,6-diacetylpyridine(benzoylhydrazone)(N4-phenylsemicarbazone) (H₂L³) give yellow products of the composition [UO₂(L)]. The neutral compounds contain doubly deprotonated ligands and possess uranium atoms with distorted pentagonal-bipyramidal coordination spheres. The equatorial coordination spheres of the metal atoms can be extended by the addition of a monodentate ligand such as pyridine or DMSO. The uranium atoms in the resulting complexes have hexagonal-bipyramidal coordination environments with the oxo ligands in axial positions.X-ray diffraction studies on [UO₂(L¹)(DMSO)], [UO₂(L²)], [UO₂(L²)(DMSO)] and [UO₂(L³)] show relatively short U-O bonds to the benzoylic oxygen atoms between 2.273(6) and 2.368(5) Å. This suggests a preference of these donor sites of the ligands over their imino and amine functionalities (U-N bond lengths: 2.502(7)-2.671(7) Å). The addition of a sixth ligand to the equatorial coordination sphere results in a lengthening of the metal-pyridine bonds.     

Synthesis, structure, and properties of monomeric Fe(II), Co(II), and Ni(II) complexes of neutral N-(aryl)-2-pyridinecarboxamides

We have prepared and structurally characterized six-coordinate Fe(II), Co(II), and Ni(II) complexes of types [M^II(HL¹)₂(H₂O)₂][ClO₄]₂ (M = Fe, 1; Co, 3; and Ni, 5) and [M^II(HL²)₃][ClO₄]₂ · MeCN (M = Fe, 2 and Co, 4) of bidentate pyridine amide ligands, N-(phenyl)-2-pyridinecarboxamide (HL¹) and N-(4-methylphenyl)-2-pyridinecarboxamide (HL²). The metal centers in bis(ligand)-diaqua complexes 1, 3 and 5 are coordinated by two pyridyl N and two amide O atoms from two HL¹ ligands and six-coordination is completed by coordination of two water molecules. The complexes are isomorphous and possess trans-octahedral geometry. The metal centers in isomorphous tris(ligand) complexes 2 and 4 are coordinated by three pyridyl N and three amide O atoms from three HL² ligands. The relative dispositions of the pyridine N and amide O atoms reveal that the pseudo-octahedral geometry have the meridional stereochemistry. To the best of our knowledge, this work provides the first examples of structurally characterized six-coordinate iron(II) complexes in which the coordination is solely by neutral pyridine amide ligands providing pyridine N and amide O donor atoms, with or without water coordination. Careful analyses of structural parameters of 1-5 along with that reported in the literature [M^II(HL¹)₂(H₂O)₂][ClO₄]₂ (M = Cu and Zn) and [Co^III(L²)₃] have allowed us to arrive at a number of structural correlations/generalizations. The complexes are uniformly high-spin. Spectroscopic (IR and UV/Vis) and redox properties of the complexes have also been investigated.     

Hydrothermal synthesis, structural determination, and thermal properties of 2-D cobalt- and nickel-based coordination polymers incorporating pendant-arm 3-pyridinecarboxylate ligands

Hydrothermal synthesis has afforded a family of four coordination polymers containing divalent nickel or cobalt and pendant-arm pyridylcarboxylate ligands. Utilizing 3-pyridylacetic acid and appropriate metal precursors produced [M(3-pyrac)₂(H₂O)₂] phases (M = Co (1); M = Ni (2)), while 3-pyridylpropionic acid generated [M(3-pyrprop)₂(H₂O)₂] coordination polymers (M = Co (3); M = Ni (4)). Single crystal X-ray diffraction revealed that 1-4 all display discrete 2-D layers with (4,4)-topology, anchored via bridging 3-pyridylcarboxylate ligands bearing monodentate carboxylate termini. Intralamellar hydrogen bonding between the aquo ligands and unligated carboxylate oxygen atoms is observed within 1-4. The pseudo 3-D structures of 1-4 are further assembled via stacking of individual neutral layers by interlayer hydrogen bonding. Thermal properties are also discussed.     

Cobalt(II) complexes of the antibiotic sulfadiazine, the X-ray single crystal structure of [Co(C10H9N4O2S)2(CH3OH)2]

Cobalt(II) complexes of sulfadiazine formulated as [Co(C₁₀H₉N₄O₂S)₂(CH₃OH)₂] and [Co(C₁₀H₉N₄S)₂(H₂O)₂] have been synthesized and characterized by elemental analysis, infrared and UV-Vis spectroscopy and magnetic susceptibility measurements. The crystal structures of the complex [Co(C₁₀H₉N₄O₂S)₂(CH₃OH)₂] and of free sulfadiazine are also reported. The cobalt complex and the sulfadiazine ligand both crystallize in the monoclinic space group, P21/c, with sulfadiazine acting as a bidentate ligand. Cobalt is coordinated to two-sulfonamide nitrogen and the pyrimidine nitrogen of the sulfadiazine. Two molecules of methanol complete the octahedral geometry around the cobalt, with interligand hydrogen bonding between methanol and sulfadiazine. Infrared spectroscopy confirmed the presence of water molecule in the coordination sphere of [Co(C₁₀H₉N₄S)₂(H₂O)₂]. The electronic spectra and magnetic moments of both complexes were similar, indicating that both complexes have similar structure.     

Three-dimensional iron-series coordination networks based on antiferromagnetic and ferromagnetic dinuclear motifs with mixed carboxylate and aqua bridges

Three coordination polymers of the iron-series transition metal ions with 4-(3-pyridyl)benzoic acid (4,3-Hpybz) ligand were synthesized and structurally and magnetically characterized. They have the formulas [M₂(4,3-pybz)₄(H₂O)] (M = Fe, 1; Co, 2; and Ni, 3). In these isomorphous compounds, octahedrally coordinated metal ions are linked by the mixed (μ-syn, syn-COO)₂(μ-H₂O) triple bridges to give dinuclear motifs, which serves as tetrahedral building units and are further linked by 4,3-Hpybz to give rise to diamond networks. Magnetic studies demonstrated that the (COO)₂(H₂O) triple bridges induce antiferromagnetic coupling between metal ions in 1 and 2, but compound 3 with the same mixed triple bridges exhibits ferromagnetic coupling, which may be related to orbital countercomplementarity.     

Coordination chemistry of the metalloligand [Pt2(μ-S)2(PPh3)4] with nickel(II) complexes - an electrospray mass spectrometry directed synthetic study

The reactivity of [Pt₂(μ-S)₂(PPh₃)₄] towards a range of nickel(II) complexes has been probed using electrospray ionisation mass spectrometry coupled with synthesis and characterisation in selected systems. Reaction of [Pt₂(μ-S)₂(PPh₃)₄] with [Ni(NCS)₂(PPh₃)₂] gives [Pt₂(μ-S)₂(PPh₃)₄Ni(NCS)(PPh₃)]⁺, isolated as its BPh₄ ⁻ salt; the same product is obtained in the reaction of [Pt₂(μ-S)₂(PPh₃)₄] with [NiBr₂(PPh₃)₂] and KNCS. An X-ray structure determination reveals the expected sulfide-bridged structure, with an N-bonded thiocyanate ligand and a square-planar coordination geometry about nickel. A range of nickel(II) complexes NiL₂, containing β-diketonate, 8-hydroxyquinolinate, or salicylaldehyde oximate ligands react similarly, giving [Pt₂(μ-S)₂(PPh₃)₄NiL]⁺ cations.     

Synthesis and characterization of new oligomeric and polymeric complexes based on the [Cu(bpca)] unit [Hbpca = bis(2-pyridylcarbonyl)amine]

Five novel bpca-based Cu(II) polynuclear coordination compounds [Hbpca = bis(2-pyridylcarbonyl)amine] were prepared using the [Cu(bpca)(H₂O)₂](NO₃)·2H₂O (1) building block and characterized by single crystal X-ray diffraction. We have also isolated and characterized two new crystal forms of the starting species, with lower water contents. Three of the new products are dinuclear complexes obtained by reacting 1 with different rigid or flexible spacer ligands: [Cu₂(bpca)₂(H₂O)₂(bipy)](NO₃)₂·6H₂O (2) (bipy = 4,4′-bipyridine) and [Cu₂(bpca)₂(H₂O)₂(bpete)](NO₃)₂·xH₂O (3) [bpete = (E)-1,2-di(pyridin-4-yl)ethane] are linear dumbbell-like species with Cu?Cu separations of 11.075 and 13.275 Å, respectively. The third dinuclear compound, [Cu₂(bpca)₂(H₂O)₂(bpx)](NO₃)₂·8H₂O (4) [bpx = 1,4-bis((1H-pyrazol-1-yl)methyl)benzene], with the flexible bpx ligand, assumes an unusual S-shaped conformation and shows a quite shorter Cu?Cu contact of 6.869 Å only. We have also obtained a chiral 1D neutral polymeric complex, [Cu₃(bpca)₂(bipy)₃(NO₃)₄]·6H₂O (5), that shows a central linear -Cu-bipy-Cu- chain, with all these Cu atoms connected to two lateral [Cu(bpca)(NO₃)₂]⁻ groups on two opposite sides by means of bipy spacers. An unprecedented type of Cu(II) neutral trinuclear complex, [Cu₃(bpca)₂(H₂O)₂(NO₃)₂] (6), was obtained which has a centrosymmetric structure with two external [Cu(bpca)(NO₃)₂]⁻ units chelating on a central copper atom via the two pairs of carbonyl groups of the bpca ligands. The central metal is octahedral with two axial water molecules, while the two lateral Cu atoms are in square pyramidal geometry; the Cu?Cu separation is 5.205 Å. The magnetic properties of 6 have been rationalized through a ferromagnetic coupling between the central metal ion and the peripheral ones which are coupled by a smaller antiferromagnetic interaction. DFT calculations have been also performed in order to give a better insight into magnetic interactions.     

Reversible color changes of chiral double salts of d-(+)-camphoric diammonium and transition-metal sulfates via gain and loss of crystalline and coordination water molecules

Six novel chiral double salts (1-6) composed of d-(+)-camphoric diammonium (LH₂) and transition-metal sulfates, formulated as {[M(SO₄)₂(H₂O)₄](LH₂)}·2H₂O [M = Fe(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II)], have been prepared and fully characterized including single-crystal X-ray diffraction, Fourier transform infrared (FT-IR) and vibrational circular dichroism (VCD) spectral investigations. Co(II), Ni(II) and Cu(II) compounds 2-4 exhibit reversible color changes between 20 and 140 °C via gain and loss of two crystalline and four coordination water molecules, which can be proved by their thermogravimetric (TG) and powder X-ray diffraction (PXRD) analyses. To the best of our knowledge, this is the first report on chiral double salts showing chromotropism properties.     

Synthesis,physico-chemical studies of manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II) complexes with some p-substituted acetophenone benzoylhydrazones and their antimicrobial activity

Complexes of the type [M(pabh)(H₂O)Cl], [M(pcbh)(H₂O)Cl] and [M(Hpabh)(H₂O)₂ (SO₄)] where, M = Mn(II), Co(II), Ni(II), Cu(II) and Zn(II); Hpabh = p-amino acetophenone benzoyl hydrazone and Hpcbh = p-chloro acetophenone benzoyl hydrazone have been synthesized and characterized with the help of elemental analyses, electrical conductance, magnetic susceptibility measurements, electronic, ESR and IR spectra, thermal (TGA & DTA) and X-ray diffraction studies. Co(II), Ni(II) and Cu(II) chloride complexes are square planar, whereas their sulfate complexes have spin-free octahedral geometry. ESR spectra of Cu(II) complexes with Hpabh are axial and suggest as the ground state. The ligand is bidentate bonding through >C = N ? and deprotonated enolate group in all the chloro complexes, whereas, >C = N and >C = O groups in all the sulfato complexes. Thermal studies (TGA & DTA) on [Cu(Hpabh)(H₂O)₂(SO₄)] indicate a multistep decomposition pattern, which are both exothermic and endothermic in nature. X-ray powder diffraction parameters for [Co(pabh)(H₂O)Cl] and [Ni(Hpabh)(H₂O)₂(SO₄)] correspond to tetragonal and orthorhombic crystal lattices, respectively. The ligands as well as their complexes show a significant antifungal and antibacterial activity. The metal complexes are more active than the ligand.     

Spectroscopic and magnetic properties of transition metal(II) triflouromethanesulfonate compounds with bridging asymmetric 3,4-dialkyl substituted 1,2,4-triazole ligands

The spectroscopic and magnetic properties are described of coordination compounds with asymmetric 3,4-diakyl substituted 1,2,4-triazoles. The ligands 3-methyl-4-ethyl-1,2,4-traizole and 3-methyl-4-t-butyl-1,2,4-triazole have been investigated. Using M(CF₃SO₃)₂ (M = Mn, Co, Ni, Cu, Zn) compounds have been obtained with a linear trinuclear structure, in which the metal ions are linked to each other by two pairs of three bridging triazoles. The coordination sphere around the terminal ligands is completed by monodentate ligands and/or water molecules. The structure has been confirmed by an X-ray structure determination of [Co₃(metz)₆(H₂O)₆][Co₃ (metz)₈(H₂O)₄](CF₃SO₃)₁₂(H₂O)₈. this compound crystallizes in the space group P with lattice constants a = 13.793(4), b = 14.401(3), c = 23.258(4) Å, α = 80.58(2), β = 83.23(2) and γ = 64.33(2)°. The unit cell contains two independent trinuclear clusters of different composition. These two clusters have the same overall structure. Differences are related to the presence of monodentately coordinating ligands as well as to the position of the C3-methyl substituent. The complete refinement of this structure was obstructed by disorder problems in the anions and the non-coordinating water molecules. The magnetic susceptibilities of the compounds have been recorded and could be fitted to theoretical expressions for linear trimers. The compound [Ni₂- (mtbtz)₅(H₂O)₄](CF₃SO₃)₄(H₂O)₄ appears to be a dimeric species as concluded from its magnetic behaviour.     

Ferromagnetic and antiferromagnetic spin coupling in Ni4O4 cubane-type clusters with 4-amino-3,5-bis(hydroxymethyl)-1,2,4-triazole as a ligand. The x-ray structure of a new dumbbell-like double cubane cluster

The synthesis, spectroscopic and magnetic properties of two nickel clusters are described, Ni₈(NCS)₈(Hahmt)₆(H₂ahmt)₄(ahmt)(H₂O)₁₂ (A) and Ni₄(Hahmt)₄(H₂ahmt)₂(NCS)₄(H₂O)₄ (B) (H₂ahmt = 4-amino-3,5-bis(hydroxymethyl)-1,2,4-triazole). The X-ray structure of A has been determined. The compound crystallizes in the space group C2/c, a = 25.458(2), b = 15.466(2), c = 26.959(3) Å, β = 90.648(5)°. The structure was refined to R = 0.108 for 4169 observed reflections. The structure consists of two Ni₄O₄ cubane-type clusters, each consisting of four nickel atoms, three singly deprotonated and one doubly deprotonated ligands. Hahmt coordinates as a bidentate chelating ligand through its triazole-N₁ and its 3-oxymethyl-part. The doubly deprotonated ligand chelates in a bis-bidentate manner to two Ni₄ clusters. In this way dumbbell-like pairs of ligand bridged cubanes are formed. Along two opposite diagonals of the Ni₄O₄ cubanes a neutral ligands, coordinating through its triazole-N₁,N₂ atoms, forms a bridge between two nickel ions. The NiN₃O₃ chromophore is completed by a monodentate N-coordinating thiocyanate anion. Compound B, for which only partial structure determination was possible, has the same Ni₄O₄ cubane-type cluster, however, without the bridging ligand between the cubanes. The two types of NiNi bridges result in two unequivalent superexchange pathways. In the compounds both ferromagnetic and antiferromagnetic interaction pathways are present, resulting in an overall antiferromagnetic behaviour. The nature of the interaction for the different pathways is related to the observed NiONi angles. The intercluster exchange is much larger through the triazole bridge in A than it is in B, where only hydrogen bridges keep the clusters together.     

Substitution effect on new Co(II) addition compounds with salicylaldehydes and the nitrogenous bases phen or neoc: Crystal and molecular structures of [Co(5-NO2-salicylaldehyde)2(phen)], [Co(5-CH3-salicylaldehyde)2(neoc)] and [Co(5-Cl-salicylaldehyde)2(neoc)]

The cobalt(II) addition compounds [Co(X-salo)₂(Y)], where X-salo is the anion of substituted salicylaldehydes (X = 3-OCH₃, 5-CH₃, 5-Cl, 5-NO₂ and Y = the neutral 1,10 phenanthroline or neocuproine), were synthesized and characterized by physicochemical and spectral (IR, UV-Vis) data. Theoretical calculations (DFT, ZINDO, TD DFT) with gaussian 03 for the prediction of the electronic spectrum for the compounds, gave good correlation with the experimental one in the solid state and in solution. The cyclic voltammetry study in CH₃CN gave all the expected waves for the redox processes of the metal Co(II) and the ligands phen or neoc and salicylaldehydes. The X-ray diffraction study of three compounds [Co(5-NO₂-salo)₂(phen)], [Co(5-CH₃-salo)₂(neoc)] and [Co(5-Cl-salo)₂(neoc)] verified their analogous proposed octahedral arrangement of the ligands around the cobalt(II) atom.