Synthesis, structures and magnetic properties of nicotinato-copper(II) complexes with polybenzimidazole and polyamine ligands

Four novel nicotinato-copper(II) complexes containing polybenzimidazole and polyamine ligands were synthesized with formula [Cu₂(bbma)₂(nic)₂](ClO₄)₂·CH₃OH·0.5H₂O (1), [Cu₂(dien)₂(nic)₂](ClO₄)₂·2CH₃OH (2), [Cu(ntb)(nic)]ClO₄·H₂O (3) and [Cu(tren)(nic)]BPh₄·CH₃OH·H₂O (4), in which bbma is bis(benzimidazol-2-yl-methyl)amine, dien is diethylenetriamine, ntb is tris(2-benzimidazolylmethyl)amine, tren is tris(2-aminoethyl)amine and nic is nicotinate anion. All of the complexes were characterized by elemental analysis, IR and X-ray diffraction analysis. Complexes 1 and 2 contain centrosymmetric dinuclear entity with the two Cu(II) atoms bridged by two nicotinate anions in an anti-parallel mode. The Cu···Cu separation is 7.109 Å for 1 and 6.979 Å for 2. Complexes 3 and 4 are mononuclear with nicotinate coordinated to Cu(II) ion by the carboxylate O atom in 3 and the pyridine N atom in 4. All of the complexes exhibit abundant hydrogen bonds to form 1D chain for 1, 3, 4 and 2D network for 2. Magnetic susceptibility measurements over the 2-300 K range reveal very weak ferromagnetic interaction between the two Cu(II) ions in 1 and antiferromagnetic interaction in 2 mediated by nicotinate ligand, with J value to be 0.15 and −0.19 cm⁻¹, respectively.     

Zinc complexes with tricarballylic acid and Lewis bases with zero- and two-dimensional structures

Three ternary zinc complexes of the open chain polycarboxylic acid, tricarballylic (1,2,3-propane-tricarboxylic) acid (PTCH₃) have been isolated and characterized with crystallographic and physicochemical techniques. [Zn(PTCH)(phen)(H₂O)]₂ · 4H₂O (1) (where phen = 1,10-phenanthroline) has a unique dinuclear structure, while [Zn(PTCH)(bpy)]_n · 3nH₂O (2) and [Zn(PTCH)(epy)]_n · 4nH₂O (3) (where bpy = 4,4′-bipyridine and epy = 1,2-bis(4-pyridine)ethane) have 2D polymeric structures. The bis-deprotonated ligand, in all three complexes, uses for coordination only two oxygen atoms, which belong to the same carboxylate in 1, and to two different carboxylates in 2 and 3.     

Construction of three one-dimensional zinc(II) complexes containing pyrazine-2,3-dicarboxylic acid

Three one-dimensional zinc complexes, namely, [Zn(pzdc) · 3H₂O] · H₂O (1), [Zn₂(pzdc)₂ · 4H₂O] · 2.5H₂O (2), and [Zn(pzdc)(phen) · 4H₂O]_n (3) (H₂pzdc, pyrazine-2,3-dicarboxylic acid, phen = 1,10-phenanthroline), have been synthesized successfully under hydrothermal condition. X-ray diffraction analyses reveal that complex 1 is a square-wave-like chain and complex 2 shows a 1D ladder-like infinite chain, while complex 3 has 1D zigzag chain structure. In all cases, the Zn(II) centers have octahedral coordination geometries. Through hydrogen bonding (such as O-H···O, O-H···N and C-H···O) and/or π-π stacking interactions, three-dimensional supramolecular networks are constructed in three complexes. Furthermore, the IR, TGA and luminescent properties are also investigated in this work.     

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.     

Zinc(II) complexes with 1,8-naphthyridine-based ligand: Crystal structures and luminescent properties

The reactions of 2,4-dimethyl-7-(2-pyridylamino)-1,8-naphthyridine (L1) with Zn(ClO₄)₂ · 6H₂O, and bis(5,7-dimethyl-1,8-naphthyrid-2-yl)amine ligand (L2) with Zn(OAc)₂ · 2H₂O, ZnCl₂ or Zn(ClO₄)₂ · 6H₂O afforded four blue luminescent zinc(II) complexes, [Zn(L1)₂](ClO₄)₂ · 2CH₂Cl₂ (1), [Zn(L2)(OAc)₂] · CH₂Cl₂ (2), [Zn(L2)₂][ZnCl₄] · 3.5CH₂Cl₂ (3) and [Zn(L2)₂](ClO₄)₂ (4), respectively. Crystal structures of complexes 1-3 have been determined by X-ray structural analyses as mononuclear complexes with pseudo-tetrahedral geometry. The crystal packing of 1 reveals the coordination cation which is self-assembled to stair chains through aromatic π-π interactions. The intermolecular N-H?O hydrogen bond in 2 generates a centrosymmetric H-bonded dimer. However, the crystal lattice of 3 shows that the molecules are linked by extensive intermolecular hydrogen bonds between the amino groups and the anions, resulting in a one-dimensional zigzag chain. Furthermore, these molecular pairs or chains were self-assembled to two-dimensional sheets or three-dimensional networks through aromatic π-π interactions. All the zinc(II) complexes display intense intraligand ¹(π-π^∗) fluorescence with λ_max at 380 and 393 nm for 1, 385 and 404 nm for 2-4 in methanol at room temperature, respectively. Emission quantum yields of these complexes are in the range from 0.41 to 0.57. The broad emission bands in their solid-state emission spectra are attributed to intraligand ¹(π-π^∗) transition and aromatic π-π interactions as well.     

Dicarbonyliridium(I) complexes of pyridine ester ligands and their reactivity towards various electrophiles

The reaction of dimeric precursor [Ir(CO)₂Cl]₂ with two molar equivalent of the pyridine-ester ligands (L) like methyl picolinate (a), ethyl picolinate (b), methyl nicotinate (c), ethyl nicotinate (d), methyl isonicotinate (e) and ethyl isonicotinate (f) affords the tetra coordinated neutral complexes of the type [Ir(CO)₂ClL] (1a-f). The single crystal X-ray structure of 1d reveals that the Ir atom occupies the centre of an approximately square planar geometry with two CO groups cis- to each other. Intermolecular C-H?O and Ir?C interactions greatly stabilize the supramolecular structure of 1d in the solid state. The oxidative addition (OA) reactions of 1a-f with different electrophiles such as CH₃I, C₂H₅I and I₂ undergo decarbonylation of one CO group to generate the oxidized products of the type [Ir(CO)RClIL] where R = -CH₃ (2a-f); -C₂H₅ (3a-f) and [Ir(CO)ClI₂L] (4a-f). Kinetic study of the reaction of 1c-f with CH₃I indicates a first order reaction which follow the order 1d > 1c > 1f > 1e. All the synthesized complexes were characterized by elemental analyses, IR, and multinuclear NMR spectroscopy.     

Metal-organic open frameworks with one-dimension channels assembled with pyridine 2,6-dicarboxylic acid and N-containing auxiliary ligands: Syntheses, crystal structures, and physical characterization

Four new complexes, {[Mn(imH)₂(pdc)]·H₂O}_n (1), [Zn₂(pdc)₂(H₂O)₅]·2H₂O (2), [Zn(imH)₂(pdc)]·H₂O (3), {[Zn₂(pdc)₂(bpy)(H₂O)₂]·5H₂O}_n (4) [imH = imidazole pdc = pyridine 2,6-dicarboxylate, bpy = 4,4′-bipyridine] have been synthesized under hydrothermal conditions and structurally characterized by elemental analysis, IR, PXRD, single-crystal X-ray diffraction and thermogravimetric analyses. All the four complexes display a three-dimensional (3D) open framework with one-dimensional (1D) channels that are filled with lattice water molecules. Particularly, in 4, the lattice water molecules form an infinite water chain. Both 1 and 4 consist of 1D polymeric chains. While 2 contains a dinuclear Zn(II) unit, and 3 is a mononuclear complex. Further, the result of thermal analysis of 1 and 2 shows the robustness of the overall supramolecular three-dimensional architecture. Complexes 1, 3, and 4 exhibit strong fluorescent emissions in the solid state at room temperature and could be significant in the field of photoactive materials.     

Syntheses, spectroscopies and structures of zinc complexes with malate

Reactions of zinc(II) ion with racemic malic acid (C₄H₆O₅ = H₃mal) result in the isolation of four new zinc(II) malato complexes: (NH₄)[Zn(R-H₂mal)₃] · H₂O (1), trans-[Zn(R-H₂mal)(S-H₂mal)(H₂O)₂] · 2H₂O (2), (NH₄)₂[Zn(R-Hmal)(S-Hmal)] · 2H₂O (3), and [Zn₂(R-Hmal)(S-Hmal)(H₂O)₄]_n · 2nH₂O (4). Three R-malic acids in 1 act as bidentate ligands via their alcoholic and the central carboxy groups with Zn(II) ion, leaving the terminal carboxylic acid groups free. The R- and S-malates of 2 coordinate in a bidentate manner with zinc ion in trans-form. In 3, Zn(II) ion is coordinated by R- and S-malates in a tridentate fashion via their alcoholic and two carboxy groups. Complex 4 forms a two-dimensional layered structure through the links of a new dimeric unit [Zn₂(R-Hmal)(S-Hmal)(H₂O)₄] with one of the oxygen atoms from the terminal carboxy group of malate ligand. The coordination of malates depends on pH variation, on Zn:malate ratio, and also on temperature. Tridentate chelation of malate in 3 is found between pH 4.5-9.0. The soluble monomeric species 1-3 have been investigated using ¹³C NMR spectra by long-time acquisition. The solution NMR spectra indicate that zinc malate complexes dissociate in H₂O (D₂O). Obvious downfield shifts of the central carboxy carbon atoms in 1-3 are observed compared with those of free malate, which indicate that these zinc malate complexes dissociate in aqueous solution.     

Extended molecular networks based on Zn and Cd imparting N-substituted imidazole

Synthesis of complexes with the formulations [M(CPI)₂Cl₂] (M = Zn, 1; M = Cd, 4) and [M(CPI)₆](X)₂ (M = Zn, X = NO₃⁻, 2; X = ClO₄⁻, 3; M = Cd, X = NO₃⁻, 5; X = ClO₄⁻, 6) have been achieved from the reactions of MCl₂, M(NO₃)₂·xH₂O and M(ClO₄)₂·xH₂O (M = Zn, Cd) with 1-(4-cyanophenyl)-imidazole (CPI). Complexes 1-6 have been characterized by elemental analyses and spectral studies (IR, ¹H, ¹³C NMR, electronic absorption and emission). Molecular structures of 1, 2, 3 and 6 have been determined crystallographically. Weak interaction studies on the complexes revealed presence of various interesting motifs resulting from C-H···N, C-H···Cl and π-π stacking interactions. The complexes under study exhibit strong luminescence at ∼450 nm in DMSO at room temperature.     

Topological control of the spin coupling in dinuclear copper(II) complexes with meta- and para-phenylenediamine bridging ligands

A novel series of copper(II) complexes of formula [Cu(tren)(mpda)](ClO₄)₂ · 1/2H₂O (1), [Cu₂(tren)₂(mpda)](ClO₄)₄ · 2H₂O (2), and [Cu₂(tren)₂(ppda)](ClO₄)₄ · 2H₂O (3) containing the tetradentate tris(2-aminoethyl)amine (tren) terminal ligand and the potentially bridging 1,n-phenylenediamine [n = 3 (mpda) and 4 (ppda)] ligand have been prepared and spectroscopically characterized. X-ray diffraction on single crystals of 1 and 3 show the presence of mono- (1) and dinuclear (3) copper(II) units where the mpda (1) and ppda (3) ligands adopt terminal monodentate (1) and bridging bis(monodentate) (3) coordination modes toward [Cu(tren)]²⁺ cations with an overall non-planar, orthogonal disposition of the phenylene group and the N-Cu-N threefold axis of the trigonal bipyramid of each copper(II) ion [values of the Cu-N-C-C torsion angle (?) in the range of 50.8(3)-79.2(2) (1) and 80.9(2)-86.5(2)° (3)]. Variable-temperature magnetic susceptibility measurements on the dinuclear complexes 2 and 3 show the occurrence of moderate ferromagnetic (J = +8.3 cm⁻¹, 2) and strong antiferromagnetic (J = −51.4 cm⁻¹, 3) couplings between the two copper(II) ions across the meta- and para-phenylenediamine bridges, leading to S = 1 (2) and S = 0 (3) ground spin states [H = −JS₁ · S₂ with S₁ = S₂ = S_Cu = 1/2]. Density functional theory (DFT) calculations on the triplet (2) and broken-symmetry (BS) singlet (3) ground spin states, support the occurrence of a spin polarization mechanism for the propagation of the exchange interaction through the predominantly π-type orbital pathway of the 1,n-phenylenediamine bridge. Finally, a new magneto-structural correlation between the magnitude of the magnetic coupling (J) and the Cu-N-C-C torsion angle (?) has been found which reveals the role of σ- versus π-type orbital pathways in the modulation of the magnetic coupling for m- and p-phenylenediamine-bridged dicopper(II) complexes.     

Heterometallic Ni/Zn amine complexes possessing extended 2D and 3D hydrogen-bonded networks prepared from zinc oxide

Five novel heterometallic Ni/Zn coordination compounds [Ni(en)₃][ZnCl₄] (1), [Ni(en)(Hea)₂][ZnCl₄] (2), [Ni(dien)₂][ZnCl₄] (3), [Ni(en)₃][ZnCl₄] · 2DMSO (4) and [Ni(en)₃][Zn(NCS)₄] · CH₃CN (5), where en = ethylenediamine (ethane-1,2-diamine), Hea = monoethanolamine (2-aminoethanol) and dien = diethylenetriamine (1,4,7-triazaheptane), have been synthesized by means of the open-air reaction of zinc oxide, nickel chloride (or nickel powder), NH₄X (X = Cl, NCS) and ligand (en, dien, Hea) in non-aqueous solvents, such as DMSO, DMF, CH₃OH and CH₃CN. The choice of a counter-anion in the initial ammonium salt as well as selection of the ligand and solvent provides an effortless approach to the controlled assembly of two- or three-dimensional extended networks assisted by hydrogen bonding. Crystallographic investigations reveal that 1, 2 and 5 possess 3D, while 3 and 4 exhibit 2D H-bonded crystal structures. The structures of the compounds exhibit six-coordinated Ni(II) centers and four-coordinated Zn(II) centers in distorted octahedral and tetrahedral geometries, respectively.     

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.     

Synthesis, characterization, and reactivity of zinc carboxylate complexes of 2,3-pyridine dicarboxylic acid and (3-oxo-2,3-dihydro-benzo[1,4]oxazin-4-yl)acetic acid

Ethylenediammonium tris-2,3-pyridine dicarboxylato zinc(II) trihydrate (enH₂)₂[ZnL₃]·2H₂O (1) (where H₂L = 2,3-pyridine dicarboxylic acid, en = ethylenediamine) and a mixed metal coordination polymer with composition [Na₂ZnL′₃(OAc)(H₂O)₃]_n (2) {where L′ = anion of (3-oxo-2,3-dihydro-benzo[1,4]oxazin-4-yl)acetic acid} are synthesized and characterized. The complex 1 is mono nuclear complex with three coordinating carboxylate anion along with nitrogen chelating zinc ion and there is three uncoordinated carboxylate group one each from three ligand molecules making a complex anion of zinc(II). The zinc(II) ion are in distorted octahedral coordination geometry. In this complex diprotonated ethylenediamines serve as cations. The complex 2 has a polymeric structure with one acetate and three carboxylate of L′ binding to zinc ion provides a tetrahedral environment and these ligands further hold dinuclear units of tri-aquated sodium ions; each dinuclear sodium units are bridged by one water molecule make the coordination polymer. The catalytic ability of these two complexes 1 and 2 towards carbon-carbon bond formation reaction between 3,4-dimethoxy benzaldehyde and acetone are studied. Both the complexes as well as sodium salt of L′ are found to be catalyst for such reactions.     

Synthesis, and characterization of cobalt(III) complexes with Schiff bases derived from 2-hydroxynaphthaldehyde, (naph)2dien and (naph)2dpt, and monodentate amine ligands: Crystal structure, spectral and redox properties

Two series of complexes of the type [Co^III{(naph)₂dien}(amine)]BPh₄ {(naph)₂dien = bis-(2-hydroxy-1-naphthaldimine)-N-diethylenetriamine dianion, and amine = piperidine (pprdn) (1), pyrrolidine (prldn) (2), pyridine (py) (3), N-methylimidazole (N-MeIm) (4)}, and [Co^III{(naph)₂dpt}(amine)]BPh₄ {(naph)₂dpt = bis-(2-hydroxy-1-naphthaldimine)-N-dipropylenetriamine dianion, and amine = piperidine (pprdn) (5), 3-methylpyridine (3-Mepy) (6)} have been synthesized and characterized by elemental analyses, IR, UV-Vis, and ¹H NMR spectroscopy. The crystal structures of (2) and (6) have been determined by X-ray diffraction. The redox potentials of the central cobalt ion show a relatively good correlation with the σ-donor ability of the axial ligands. The spectroscopic and electrochemical properties of these complexes are also influenced by the mutual steric hindrance between the pentadentate Schiff base and the ancillary ligands.     

Syntheses and characterization of five d coordination polymers derived from phenanthroline derivative and dicarboxylate mixed ligands

Five structurally diverse complexes, [Cd₂(pyip)₂(suc)₂]_n·1.5nH₂O (1), [Zn(pyip)(glu)]_n (2), [Cd(pyip)(glu)]_n (3), [Zn(pyip)₂(adip)₂]_n·2.5nH₂O (4), [Cd₃(pyip)₂(adip)₃]_n (5) (pyip = 2-(pyridin-3-yl)-1H-imidazo[4,5-f][1,10]phenan-throline, H₂suc = succinic acid, H₂glu = glutaric acid, H₂adip = adipic acid), have been hydrothermally synthesized. Complexes 1 and 4 are ribbon-like chains, in which pyip ligands attach to the both sides of the chain in pairs. Complex 2 is a one dimensional (1D) wave-like chain, while the pyip ligands attach to only one side of the chain. Complexes 3 and 5 are both two dimensional (2D) networks, in which the dicarboxylate ligands connect the dinuclear or trinuclear Cd^II units into layers with (4, 4) topological network. The structural differences among these complexes show that the organic acids have important influences on the final structures.     

Synthesis, crystal structures and characterization of three novel complexes with N-[2-(2-hydroxybenzylideneamino)ethyl]-4-methyl-benzene-sulfonamide as ligand

Reaction of the N-tosyl-ethylenediamine and salicylaldehyde forms a new sulfonamide Schiff base N-[2-(2-hydroxybenzylideneamino)ethyl]-4-methyl-benzene-sulfonamide (H₂L). Three novel complexes constructed from H₂L, namely, [M(HL)₂] · xH₂O (M = Cu, x = 0 for 1, M = Ni, x = 0 for 2 and M = Zn, x = 1 for 3) have been prepared and characterized via X-ray single-crystal diffraction, elemental analysis, X-ray powder diffraction (XRPD), FT-IR, UV-Vis, TGA and photoluminescence measurements. Complex hydrogen bonds, C-H···π and π-π stacking interactions lead 1-3 to present 1-D, 2-D and 3-D supramolecular architectures, respectively.     

Synthesis and structures of zinc complexes with new binucleating ligands containing alkoxide bridges, and their activities in the hydrolysis of tris(p-nitrophenyl)phosphate

Four new binucleating ligands featuring a hydroxytrimethylene linker between two coordination sites (1,3-bis{N-[3-(dimethylamino)propyl]-N-methylamino}propan-2-ol, HL¹; 1,3-bis{N-[2-(dimethylamino)ethyl]-N-methylamino}propan-2-ol, HL²; 1,3-bis[bis(2-methoxyethyl)amino]propan-2-ol, HL³; and 1-bis[(2-methoxyethyl)amino]-3-{N-[2-(dimethylamino)ethyl]-N-methylamino}propan-2-ol, HL⁴) were synthesized, along with the corresponding zinc complexes. The structures of three dinuclear zinc complexes ([Zn₂L¹(μ-CH₃COO)₂]BPh₄ (1), [Zn₂L³(μ-CH₃COO)₂]BPh₄ (3), and [Zn₂L⁴(μ-CH₃COO)(CH₃COO)(EtOH)]BPh₄ (4)) and a tetranuclear zinc complex ({[Zn₂L²(μ-CH₃COO)]₂(μ-OH)₂}(BPh₄)₂ (2)) were revealed by X-ray crystallography. Hydrolysis of tris(p-nitrophenyl)phosphate (TNP) by these zinc complexes in an acetonitrile solution containing 5% Tris buffer (pH 8.0) at 30 °C was investigated spectrophotometrically and by ³¹P NMR. Although zinc complexes 1, 3, and 4 did not show hydrolysis activity, the tetranuclear zinc complex 2, containing μ-hydroxo bridges, was capable of hydrolyzing TNP. This suggests that the hydroxide moiety in the complex may have an important role in the hydrolysis reaction.     

[S2], [S3], and [N3] coordination modes of hydrotris(thioxotriazolyl)borato. Zinc, nickel, cobalt, and bismuth complexes

The ligand hydrotris(1,4-dihydro-3-methyl-4-phenyl-5-thioxo-1,2,4-triazolyl)borato (Tr^Ph,Me) was synthetized as natrium salt and the complexes [Zn(Tr^Ph,Me)₂] · 7.5H₂O · 1.5CH₃CN (2a), [Zn(Tr^Ph,Me)₂] · 8DMF (2b), [Co(Tr^Ph,Me)₂] · 8DMF (3a), [Ni(Tr^Ph,Me)₂] · H₂O · 6DMSO (4a), [Bi(Tr^Ph,Me)₂]NO₃ (5), have been isolated and structurally characterized by X-ray diffraction. In the zinc derivatives the ligand adopts different denticity and coordination modes, η² and [S₂] for 2a and η³ and [N₃] for 2b, depending on the crystallization solvent, giving rise to tetrahedral and octahedral geometry, respectively. In the octahedral cobalt and nickel complexes the ligand is η³ and [N₃] coordinated whereas in the bismuth complex the η³ and [S₃] coordination is exhibited.     

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.     

The effect of organic acid on self-assembly process: Syntheses and characterizations of six novel cadmium(II)/zinc(II) complexes derived from mixed ligands

Using the principle of crystal engineering, six metal-organic coordination polymers, [Cd(bdc)(3-pytpy)]_n · 2nH₂O (1), [Cd(bdc)_0.5(3-pytpy)]_n · n(ClO₄) (2), Cd(ndc)_0.5(3-pytpy)]_n · n(ClO₄) (3), [Zn(ndc)(3-pytpy)]_n (4), [Cd(bqdc)(3-pytpy)]_n (5), and [Zn(pam)(3-pytpy)]_n · 2nH₂O (6) (H₂bdc = benzene-1,4-dicarboxylic acid, H₂ndc = naphthalene-2,6-dicarboxylic acid, H₂bqdc = 2,2′-biquinoline-4,4′-dicarboxylic acid, H₂pam = pamoic acid), were synthesized and structurally characterized by elemental analyses, IR spectroscopy, and single-crystal X-ray diffraction analyses. Compounds 1-6 crystallize in the presence of organic-acid linkers as well as multi-functional N-donor ligand 4′-(3-pyridyl)-2,2′:6′,2′′-terpyridine (3-pytpy). In complexes 1, 4, 5, and 6, the dicarboxylate as bridging ligand connects metal atoms to form the main body of 1D zigzag chains for 1 and 4, nearly linear chain for 5 and helical chain for 6, while 3-pytpy as tridentate chelating ligand is just like lateral arm grafting on both sides of these chains. In complexes 2 and 3, both the dicarboxylate and 3-pytpy as bridging ligands connect metal atoms into 2D polymeric structure for 2 and 1D chain of alternating loops and rods for 3. The weak interactions such as hydrogen bonding and π···π stacking were investigated on the formation of superamolecular structures and the influence of organic acid on the formation of the final structures was discussed. In addition, the photoluminescent properties of 1-6 were also determined.