Effects of steric/basic properties of Lewis bases on the degree of aggregation of zinc(II) pivalate complexes

A triangular [Zn₃(μ₃-OH)(OC(O)^tBu)(μ₂-κ¹O:κ¹O′-O₂C^tBu)₄(3,5-lutidine)₃] (1), a paddlewheel based dinuclear [Zn(μ₂-κ¹O:κ¹O′-O₂C^tBu)₂L]₂ [L = 2,4-lutidine (2), 3,4-lutidine (3), and 2,3-lutidine (4)] and an hourglass based linear trinuclear [Zn₃(μ₂-κ¹O:κ¹O′-O₂C^tBu)₆(pyridine)₂] (5) complexes were synthesized to understand the role of subtle steric/basic properties of Lewis bases on the degree of aggregation of the products. The mononuclear Zn(OC(O)^tBu)₂·2H₂O was also prepared in order to probe the origin of the μ₃-OH moiety in complex 1. Complexes 1-5 and Zn(OC(O)^tBu)₂·2H₂O were characterized by microanalytical, IR, TGA/DTA, solution (¹H and ¹³C) NMR, solid-state cross-polarization magic angle spinning (CP-MAS) ¹³C NMR, mass spectral data and single crystal X-ray diffraction data. Complex 1 represents the first example of a discrete trinuclear zinc(II) carboxylate complex that contains a [Zn₃(μ₃-OH)]⁵⁺ core with zinc atoms in three distinct geometries namely a distorted tetrahedral, trigonal bipyramidal, and octahedral. A plausible mechanism for the formation of complexes 1-5 was explained with the aid of point zero charge (pzc) model.     

Binuclear copper and zinc complexes based on polypyridyl ligand 2,3,5,6-tetra(2-pyridyl)pyrazine (tppz): Synthesis, spectral and structural characterization

The reaction of MCl₂ · 2H₂O (M = Cu, Zn) with 2,3,5,6-tetra(2-pyridyl)pyrazine (tppz) (referred hereafter as L) in 2:1 molar ratio in acetonitrile at room temperature afforded binuclear complexes [M₂(κ³-L)Cl₄] [Cu (1), Zn (2)] where the ligand is bis-tridentate manner. The complexes have been characterized by elemental analyses, FAB-MS, IR, EPR, NMR and electronic spectral studies. Solid state structures of both the [Cu₂(κ³-L)Cl₄] · 5H₂O (1), [Zn₂(κ³-L)Cl₄] · H₂O (2) have been determined by single crystal X-ray analyses. A well-resolved uudd cyclic water tetramer and water monomer were reported in the crystal host of [Cu₂(κ³-L)Cl₄] · 5H₂O (1) and [Zn₂(κ³-L)Cl₄] · H₂O (2) showing the contribution of the water cluster to the stability of the crystal host 1 and 2.     

Cadmium(II) and zinc(II) coordination polymers with mixed building blocks of benzenedicarboxyl and 2,5-bipyridyl-1,3,4-oxadiazole: Syntheses, crystal structures, and properties

Three Cd(II) and Zn(II) coordination polymers, including {[Cd(3-bpo)(mip)(H₂O)](H₂O)₂}_n (1), {[Cd(4-bpo)(hip)(H₂O)](H₂O)₄}_n (2), and {[Zn(4-bpo)(tp)](CH₃OH)}_n (3) were synthesized from the reactions of Cd^II or Zn^II nitrate with mixed organic ligands [3-bpo = 2,5-bis(3-pyridyl)-1,3,4-oxadiazole, H₂mip = 5-methylisophthalic acid, 4-bpo = 2,5-bis(4-pyridyl)-1,3,4-oxadiazole, H₂hip = 5-hydroxylisophthalic acid, H₂tp = terephthalic acid] under the similar layered diffusion condition. The resulting crystalline materials 1-3 were characterized by IR, microanalysis, powder X-ray diffraction (PXRD) techniques. Single-crystal X-ray diffraction indicates a 1-D tubular motif for 1, a 1-D dual-track array for 2, and a 2-D grid-like pattern for 3, constructed via different metal-ligand coordination contacts. Higher-dimensional supramolecular architectures are further assembled in 1-3 via H-bonding and aromatic stacking interactions. In addition, thermal stability and fluorescence of these polymeric complexes were also investigated and discussed.     

Manganese(II) and zinc(II) compounds via amino acid derivatives: Effects of temperature and solvents

To investigate the influence of temperature and the ratios of solvents on the design and synthesis of metal-organic frameworks (MOFs), we have synthesized and structurally characterized a series of supramolecular assemblies based on different amino acid derivatives and nitrogen-containing heterocyclic ligands, namely [Mn(phen)₂(phth)(H₂O)]·4H₂O (1), [Mn(phen)₂(HL1)₂]·3.5H₂O (2), [Zn(bpp)₂(L-Me)₂] (3), and [Zn(bpp)(L-Me)₂] (4) (H₂phth = phthalic acid, H₂L¹ = phthalyl-l-valine, H₂L = (+)-N-tosyl-l-glutamic acid, phen = 1,10-phenanthroline, bpp = 1,3-bis(4-pyridyl)propane, and L-Me = C₁₂H₁₃NO₆S-CH₃). Compounds 1 and 2, which are assembled through noncovalent interactions, were obtained by controlling the temperature. In 1, π-π stacking and hydrogen-bonding interactions lead to stacking in a 3D supramolecular network, while in 2, π-π stacking interactions form 1D chains that extend along the c-axis. Depending on the solvents employed, compounds 3 and 4 could be generated, with a 1D bpp-connected Zn-bpp-Zn double chain that is further hydrogen-bonded into a 2D network that extends parallel to the ac plane in 3, and a single chain in 4.     

Synthesis, characterisation and crystal structures of a few coordination complexes of nickel(II), cobalt(III) and zinc(II) with N′-[(2-pyridyl)methylene]salicyloylhydrazone Schiff base

Four new coordination complexes, Ni^II(L)₂ (1), [Co^III(L)₂]ClO₄ (2), [Zn(HL)(L)]ClO₄ · H₂O (3) and [Zn(L)₂][Zn(L)(HL)]ClO₄ · 7H₂O (4) (where L is a monoanion of a Schiff base ligand, N′-[(2-pyridyl)methylene]salicyloylhydrazone (HL) with NNO tridentate donor set), have been synthesised and systematically characterised by elemental analysis, spectroscopic studies and room temperature magnetic susceptibility measurements. Single crystal X-ray diffraction analysis reveals that 1 is a neutral complex, while 2-4 are cationic complexes. Among them, 4 is a rare type of cationic complex with two molecules in the asymmetric unit. The ligand chelates the metal centre with two nitrogen atoms from the pyridine and imino moieties and one oxygen atom coming from its enolic counterpart. All the reported complexes show distorted octahedral geometry around the metal centres, with the two metal-N (imino) bonds being significantly shorter than the two metal-N (Py) bonds.     

Synthesis, crystal structures and properties of novel zinc(II) and cadmium(II) polymeric and cyclic bimetallic complexes with fluconazole and dicarboxylate co-ligands

Four new fluconazole-bridged zinc(II) and cadmium(II) complexes with dicarboxylate co-ligands, namely [Zn(HFlu)(TPA)]_n (1), {[Cd(HFlu)₂(TPA)]·2CH₃OH}_n (2), [Zn(HFlu)₂(Suc)(H₂O)₂]·H₂O (3), and [Cd(HFlu)₂(Suc)(H₂O)₂]·H₂O (4), have been synthesized and characterized by elemental analysis, IR, TG, and single-crystal X-ray diffraction (HFlu = 2-(2,4-difluorophenyl)-1,3-bis(1,2,4-triazol-1-yl)-propan-2-ol, H₂TPA = terephthalic acid, and H₂Suc = succinic acid). Complex 1 displays a 2-D corrugated network with common (4,4) topology, in which two types of grids constructed by two bridging TPA dianions and two HFlu ligands are found. Complex 2 shows an unusual (3,6) coordination layer consisting of alternative PMPM Cd-HFlu helical chains in which the Cd(II) nodes are also fixed by terephthalate dianions in a cis fashion. The isostructural complexes 3 and 4 have 20-membered dimeric macrocyclic motifs with the Zn···Zn and Cd···Cd distances of 11.258(2) and 11.528(2) Å, respectively. The fluorescence and thermal stability of complexes 1-4 have also been investigated.     

Syntheses, structures and photoluminescence properties of cadmium(II) and zinc(II) complexes with pyridinylcarboxamide-containing ligand

Four new coordination complexes [Cd(DPBA-3)₂(H₂O)₂](ClO₄)₂·2H₂O (1), [Cd(DPBA-3)(DMF)(NO₃)₂]·DMF (2), [Cd₃(DPBA-3)₂(SCN)₆]·2DMF·4H₂O (3) and [Zn(DPBA-3)(SCN)₂] (4) [DPBA-3 = N,N′-di(pyridin-3-yl)pyridine-3,5-dicarboxamide] have been synthesized and characterized by elemental analysis, IR and single crystal X-ray diffraction. Complexes 1, 3 and 4 exhibit three different types of one-dimensional (1D) chain structures constructed by the metal ions and DPBA-3 ligands, and the Cd(II)-DPBA-3 1D chains in 3 are further linked by bridging SCN⁻ ligands to afford a three-dimensional (3D) framework. Complex 2 possesses a (6,3) two-dimensional (2D) layer structure. In 1-4, the hydrogen bonds involving the amide groups play important role to stabilize the resultant frameworks. The photoluminescence properties of the DPBA-3 and the complexes were studied in the solid state at room temperature.     

Crystal structures and luminescent properties of zinc(II) and cadmium(II) compounds constructed from 5-sulfoisophthalic acid and flexible bis-triazole ligands

Four new cadmium(II) and zinc(II) coordination polymers {[Zn(btrp)(SIP)][Zn_0.5(H₂O)₃]}_n (1), {[Cd_1.5(btrp)(SIP)(H₂O)₂]·2H₂O}_n (2), {[Cd_1.5(btrb)(SIP)(H₂O)₃]·2H₂O}_n (3), {[Zn_1.5(btrb)_1.5(SIP)(H₂O)₂]·2H₂O}_n (4) (btrp = 1,3-bis(1,2,4-triazol-1-yl)propane, btrb = 1,3-bis(1,2,4-triazol-1-yl)butane, NaH₂SIP = 5-sulfoisophthalic acid monosodium salt) have been synthesized under hydrothermal conditions and structurally characterized. Compound 1 possesses an infinite 1D ladder-like chain structure with [Zn(H₂O)₆]²⁺ trapped in the pores, which is further interconnected by π?π interactions to lead to a 2D supramolecular architecture. Compounds 2 and 3 features two similar 2D layer structures, and the resulting 2D structures are interconnected by hydrogen-bond interactions to lead to 3D supramolecular architectures. Compound 4 is a 2D parallel ladder structure, and through the interpenetrating btrb ligand, it constructs into 3D architectures. Luminescence analyses were performed on all the four compounds, which show strong fluorescent emissions in the solid state at room temperature.     

Molecular interactions of zinc(II) cyclams with polycarboxylato ligands

Four new zinc(II) cyclams of the composition {Zn(L)(tp²⁻) · H₂O}_n (1), {Zn(L)(H₂bta²⁻) · 2H₂O}_n (2), [Zn₂(L)₂(ox²⁻)] 2ClO₄ · 2DMF (3), and Zn(L)(H₂btc⁻)₂ · 2DMF (4), where L = cyclam, tp²⁻ = 1,4-benzenedicarboxylate ion, H₂bta²⁻ = 1,2,4,5-benzenetetracarboxylate ion, ox²⁻ = oxalate ion, DMF = N,N-dimethylformamide, and H₂btc⁻ = 1,3,5-benzenetricarboxylate ion, have been synthesized and structurally characterized by a combination of analytical, spectroscopic and crystallographic methods. The carboxylato ligands in the complexes 1-4 show strong coordination tendencies toward zinc(II) cyclams with hydrogen bonding interactions between the pre-organized N-H groups of the macrocycle and oxygen atoms of the carboxylato ligands. The macrocycles in 1, 2, and 4 adopt trans-III configurations with the appropriate R,R,S,S arrangement of the four chiral nitrogen centers, respectively. However, the complex 3 shows an unusual cis V conformation with the R,R,R,R nitrogen configuration. The finding of strong interactions between the carboxylato ligands and the zinc(II) ions may provide additional knowledge for the improved design of receptor-targeted zinc(II) cyclams in anti-HIV agents.     

Alteration of molecular conformations and spectral properties for nickel(II), zinc(II) and copper(II) complexes having 3,8-di(thiophen-2′,2′′-yl)-1,10-phenanthroline ligands

Four transition metal complexes of 3,8-di(thiophen-2′,2″-yl)-1,10-phenanthroline (dtphen), formulated as [Ni(dtphen)₂(H₂O)₂]·(ClO₄)₂ (1), [Zn(dtphen)₂(H₂O)]·(ClO₄)₂ (2) [Cu(dtphen)₂(H₂O)]·(ClO₄)₂ (3), [Cu(dtphen)(phen)₂]·(ClO₄)₂ (4) (phen = 1,10-phenanthroline) with different metal-to-ligand ratios, were synthesized and characterized herein. The X-ray single-crystal diffraction studies of 1-4 exhibit that different molecular configurations for the dtphen ligand can be observed where the side thiophene rings adopt the trans/trans, trans/cis, trans/disorder and cis/cis conformations relative to the central 1,10-phenanthroline unit in different compounds. Fluorescence emission spectra of 1-4 in methanol show that the fluorescence emission of 2 is much stronger than the other three metal complexes, which is mainly due to its full d¹⁰ electronic configuration of Zn(II) ion.     

Potential tridentate salicylaldehyde hydrazone of arylalkanoic acid coordinate to copper(II) acting as dinegative tetradentate ligands

A chiral Schiff base N-(S)-2-(6-methoxylnaphthyl)-propanoyl-N′-(2-hydroxylbenzylidene)hydrazine (H₂L) has been synthesized. Reaction of H₂L with Cu(OAc)₂ · H₂O led to the formation of a metal complex {[CuL] · H₂O · 2DMF}_∞ (1). In complex 1, the potential dinegative tridentate L²⁻ ligand acting as tetradentate bridging ligand coordinate to two metal ions so as to form a novel infinite metal-organic coordination chain structure. The enantiomerically pure ligand H₂L presents two different sets of signals in the ¹H NMR spectrum either in chloroform solution or in dimethylsulfoxide solution, showing the presence of both (E) and (Z) isomers. The X-ray structural investigations of H₂L revealed that it is the fully extended E-configuration in the solid state.     

Initial employment of pyridine-2-amidoxime in zinc(II) chemistry: Synthetic, structural and spectroscopic studies of mononuclear and dinuclear complexes

The first employment of pyridine-2-amidoxime [(py)C(NH₂)NOH] in zinc(II) chemistry is reported. The syntheses, crystal structures, and spectroscopic characterization are described for complexes [Zn(O₂CR)₂{(py)C(NH₂)NOH}₂] (R = Me; 1, Ph; 2), [Zn₂(acac)₂{(py)C(NH₂)NO}₂] (3), and [Zn(NO₃){(py)C(NH₂)NOH}₂](NO₃) (4). The reactions between Zn(O₂CR)₂·2H₂O (R = Me, Ph) or Zn(NO₃)₂·5H₂O and two equivalents of (py)C(NH₂)NOH in MeOH led to mononuclear compounds 1, 2 and 4, respectively. All three complexes contain two neutral N,N′-chelating (η²) (py)C(NH₂)NOH ligands, coordinated through the N_pyridyl and N_oxime atoms. In contrast, the use of Zn(acac)₂·H₂O in place of Zn(O₂CR)₂·2H₂O gives the dinuclear compound 3, which instead contains the anionic, η¹:η¹:η¹:μ bridging form of the organic ligand; the Zn^II atoms are doubly bridged by the diatomic oximate groups of the (py)C(NH₂)NO⁻ groups. Strong intra- and intermolecular hydrogen bonding interactions provide appreciable thermodynamic stability and interesting supramolecular chemistry for compounds 1-4. The photoluminescence properties of complexes 1-4 recorded in the solid state at room temperature are also presented.     

Hydrogen-bonded copper(II) and nickel(II) complexes and coordination polymeric structures containing reduced Schiff base ligands

Complexes [Cu(HSas)(H₂O)] · 2H₂O (H₃Sas = N-(2-hydroxybenzyl)-l-aspartic acid) (1), [Cu(HMeSglu)(H₂O)] · 2H₂O (H₃MeSglu = (N-(2-hydroxy-5-methylbenzyl)-l-glutamic acid) (2), [Cu₂(Smet)₂] (H₂Smet = (N-(2-hydroxybenzyl)-l-methionine) (3), [Ni(HSas)(H₂O)] (4), [Ni₂(Smet)₂(H₂O)₂] (5), and [Ni(HSapg)₂] (H₂Sapg = (N-(2-hydroxybenzyl)-l-aspargine) (6) have been synthesized and characterized by chemical and spectroscopic methods. Structural determination by single crystal X-ray diffraction studies revealed 1D coordination polymeric structures in 2 and 4, and hydrogen-bonded network structure in 5 and 6. In contrast to previously reported coordination compounds with similar ligands, the phenol remains protonated and bonded to the metal ions in 2 and 4, and also probably in 1. However, the phenolic group is non-bonded in 6.     

Nickel(II)-, cobalt(II)-, copper(II)-, and zinc(II)-phthalate and 1-methylimidazole coordination compounds: synthesis, crystal structures and magnetic properties

Three new coordination polymers [M(Pht)(1-MeIm)₂]_n (where M=Cu (1), Zn (2), Co (3); Pht²⁻=dianion of o-phthalic acid; 1-MeIm=1-methylimidazole) and two compounds [M(1-MeIm)₆](HPht)₂ · 2H₂O (M=Co (4), Ni (5)) have been synthesized and characterized by X-ray crystallography. The structures of 1-3 (2 is isostructural to 3) consist of [M(1-MeIm)₂] building units connected by 1,6-bridging phthalate ions to form infinite chains. In complex 1, each copper(II) center adopts a square coordination mode of N₂O₂ type by two O atoms from different phthalate ions and two N atoms of 1-MeIm, whereas in 3 two independent metal atoms are tetrahedrally (N₂O₂) coordinated to a pair of Pht ligands and a pair of 1-MeIm molecules. There are only van der Waals interactions between the chains in 1, while the three-dimensional network in 3 is assembled by C-H?O contacts. In contrast to polymers 1-3 the structures of 4 and 5 (complexes are also isostructural) are made up of the [M(1-MeIm)₆]²⁺ cation, two hydrogen phthalate anions (HPht⁻) and two H₂O solvate molecules. The coordination around each metal(II) atom is octahedral with six nitrogen atoms of 1-MeIm. Extended hydrogen bonding networks embracing the solvate water molecules and a phthalate residue as well as the weak C-H?O interactions stabilize the three-dimensional structures. Magnetic studies clearly show that the magnetic ions do not interact with each other. Furthermore, in compound 4 we have another example of a highly anisotropic Co²⁺ ion with a rhombic g-tensor and large zero-field-splitting. The complexes were also characterized by IR and ¹H NMR spectroscopy, thermogravimetric analysis, and all data are discussed in the terms of known structures.     

Ligand-directed metal(II) coordination polymers: Unusual disorder, and photoluminescence

2,6-Dimethyl-4-phenylpyridine-3,5-dicarboxylic acid (H₂mppdc, H₂L) is firstly employed in coordination chemistry. Two metal-organic coordination polymers with a general formula of M₂L₂(4,4′-bpy)_x(H₂O)_4−2x (M = Zn or Co, x = 1 or 2) are assembled from H₂L, 4,4′-bipyridine, zinc and cobalt salt under hydrothermal conditions, and characterized by single-crystal X-ray diffraction analyses. Of the crystal structures of title compounds, L ligands, limited in the environment from 4,4′-bipyridine, array in head-to-head and head-to-tail modes which are corresponding to the 1D (1) and 3D (2) polymeric structures, respectively. Interesting disorders occur in the crystal lattice of compound 1. And compound 2 has a 3D 4² · 6¹⁰ · 8³ topology. Solid-state H₂L and 1 have expected photoluminescence at room temperature.     

Syntheses and structure of heterobimetallic helical polymeric Mo-M(II) (M = Mn, Co, Zn, Cd or Ni) complexes using a flexidentate metalloligand

A series of heterobimetallic polymeric complexes of manganese, cobalt, zinc, cadmium and nickel, [M(Mo₂O₅L₂)(MeOH)₂(H₂O)₂]_n·nH₂O {M = Mn (2), n = 1, Co (3), n = 0, Zn (4), n = 1 and Cd (5), n = 1} and [Ni(Mo₂O₅L₂)(MeOH)(H₂O)₃]_n·2H₂O·MeOH (6) have been synthesized form the reaction of [{Na₄(H₂O)₄(μ-H₂O)₂} ⊂ (Mo₂O₅L₂)₂] (1) {LH₂ = 2-(3,5-di-tert-butyl-2-hydroxybenzylamino)acetic acid} with the corresponding metal salts. The complexes have been structurally characterized. The Complexes, 3 and 6 undergo thermal decomposition to afford mixed oxides of the type, MMoO₄·MoO₃ {M = Co or Ni}.     

Dipicolinato complexes of cobalt(II), copper(II) and zinc(II) with thiamine dications

Cobalt(II), copper(II) and zinc(II) dipicolinato complexes having thiamine dication with compositions [HT][CoL₂]·5H₂O (1), [HT][CuL₂]·5H₂O (2) and [HT][ZnL₂]·5H₂O (3) (L = dipicolinato anion, T = thiamine cation) are synthesized, characterized by X-ray diffraction and other spectroscopic techniques. The thiamine part in these complexes exists as divalent cations. The second protonation of thiamine takes place at the less crowded nitrogen atom of the pyrimidine ring. These complexes are stabilized by electrostatic and hydrogen-bonding interactions of -N⁺-H and -COO⁻ groups along with crystallized water molecules. The complexes are stable in solution as determined by ¹H NMR and visible study. The complex 1 has two medicinal components which can be easily separated by controlling pH in aqueous medium. It gets decomposed on treatment with sodium hydroxide at pH > 8 to form neutral complex {[Na₂(μ-H₂O)₃(H₂O)₃][CoL₂]·H₂O}₂.     

Copper(II)-mediated oxime-nitrile coupling in non-aqueous solutions: Synthetic, structural and magnetic studies of the copper(II)-salicylaldehyde oxime reaction system

The reactions of salicylaldehyde oxime (H₂salox) with Cu^II precursors yielded the known complexes [Cu(Hsalox)₂] (1) and [Cu(Hsalox)₂]_n (2), as well as complexes [Cu₃(salox)(L₁)(L₂)]·MeCN (3·MeCN), [CuCl(L₁)] (4) and [Cu₂Na(O₂CMe)₅(HO₂CMe)]_n (5), where L₁⁻ = o-O-C₆H₄-CHNO-C(CH₃)NH and L₂³⁻ = o-O-C₆H₄-CHNO-C(o-O-C₆H₄)N. L₁⁻ was formed in situ via the nucleophilic addition of the oximato O-atom of salox²⁻ to the unsaturated nitrile group of the MeCN reaction solvent. L₂³⁻ is also formed in situ probably through the nucleophilic attack of the oximato O-atom to the unsaturated nitrile group of salicylnitrile; the latter, although not directly added to the reaction mixture, can be produced via the dehydration of salox²⁻. Compounds 1 and 2 contain Hsalox⁻ bound to the metal center in two different coordination modes; they both contain the same mononuclear unit, however a 2D network is generated in 2 due to a relatively long Cu-O_oximato bond. Compound 3 contains three different ligands, i.e. salox²⁻, L₁⁻ and L₂³⁻, which act as μ₃-κ²O:κO′:κN, κO:κN:κN′ and μ₃-κ²O:κ²N:κO′:κN′, respectively, whereas 4 consists of a square planar Cu^II atom bound to a κO:κN:κN′ L₁⁻ and a chloride ion. Compound 5 consists of dinuclear [Cu₂(O₂CMe)₅(HO₂CMe)]⁻ units and Na⁺ ions assembled into an overall 3D network structure. Magnetic susceptibility measurements from polycrystalline samples of 2 and 5 gave best-fit parameters J = +0.36 cm⁻¹ (H = −J?_i?_j) and J = −360 cm⁻¹, zj = +20 cm⁻¹ (H = −J?_i?_j − zJ〈S_z〉?_z), respectively.     

Synthesis and characterization of Cu(II) and Ni(II) complexes of a tripodal ligand containing imidazoles

Two complexes of the formula [MH₃L](ClO₄)₂ [M = Cu(II) (1), Ni(II) (2)] have been prepared by the reaction of M(ClO₄)₂ · 6H₂O with the ligand (H₃L) formed by the Schiff base condensation of tris(2-aminoethyl)amine (tren) with three molar equivalents of 4-methyl-5-imidazolecarboxaldehyde and structurally and magnetically characterized. The structures of 1 and 2 are isomorphous with each other and with the iron(II) complex of H₃L which has been reported previously. The ligand, while potentially heptadentate, forms six coordinate complexes with both metal centers forming three M-N_imine and three M-N_imidazole bonds. The tren central N atom is at a nonbonded distance from M of 3.261 Å for 1 and 3.329 Å for 2. The neutral complex CuHL 3 was prepared by reaction of H₃L with Cu(OCH₃)₂ and the ionic complex Na[NiL] 4 was prepared by deprotonation of 2 with aqueous sodium hydroxide. Magnetic measurements of 1-3 are consistent with the spin-only values expected for S = 1/2 (d⁹, Cu(II)) and S = 1 (d⁸, Ni (II)) systems.     

Synthesis, characterization, solid-state photo-luminescence and anti-tumor activity of zinc(II) 4′-phenyl-terpyridine compounds

Reactions between 4′-phenyl-terpyridine (L) and several Zn(II) salts (sulfate, nitrate, chloride or acetate) led to the formation of the complexes [Zn₂(μ-O₂SO₂)₂L₂(CH₃OH)₂] (1), [Zn(NO₃)L(H₂O)]NO₃ (2), [Zn(Cl)₂L] (3) and [Zn(CH₃COO)₂L] (4) which were characterized by IR, ¹H NMR and fluorescence spectroscopies, elemental analysis and single crystal X-ray diffraction. In the dinuclear molecule of 1 the Zn atom is hexacoordinated, with a N₃O₃ coordination environment and forms an octagonal ZnOSOZnOSO metallacycle. In the remaining structures, the metal atom is envisaged as possessing highly distorted N₃X₂ (X = O or Cl) square pyramid coordination geometries. The structure of 3 presents two different packing patterns which lead to distinct π-π stackings. In both structures 2 and 4, strong intermolecular hydrogen bonds were identified. The complexes exhibit promising in vitro tumor-inhibiting activities, which are higher than that of cisplatin, against the following human tumor cell lines: promyelocyticfina leukaemia (HL-60), hepatocellular carcinoma (Bel-7402), gastric carcinoma (BGC-823) and nasopharyngeal carcinoma (KB).