An unprecedented coordination mode of the orotate ligand in novel polynuclear cadmium(II)–orotate complexes

Two novel carboxylate-bridged Cd(II)–orotate polynuclear complexes with 2-(2-ethylamino)pyridine (2-etapy), [Cd(μ-HOr)(2-etapy)]_n (1), and N,N-diethylethylenediamine (N,N-eten) ligands, {[Cd(μ-HOr)(H₂O)(N,N-eten)]·H₂O}_n (2) (H₃Or = orotic acid), have been synthesized and characterized by TGA–evolved gas analysis (TGA–EGA), IR spectroscopy and single crystal X-ray diffraction techniques. The orotate ligand acts as a bridging ligand with two different coordination modes, showing an unprecedented tetradentate coordination mode. The HOr ligand simultaneously chelates Cd(II) ions through the carboxylate oxygen, deprotonated pyrimidine nitrogen atoms and carboxyl oxygen atoms as a tetradentate ligand in 1. In complex 2, the HOr ligand bridges two Cd(II) ions through the carboxylate oxygen and deprotonated pyrimidine nitrogen atoms and oxygen atom of a carboxylate group of a neighbouring complex unit. Three-dimensional (3D) supramolecular structures are generated by hydrogen-bonding, and π···π and C–H···π interactions between the closest chains in both complexes.     

One-dimensional coordination polymers of Co(II) and Cd(II)-squarate with 2-methylimidazole and 4(5)-methylimidazole ligands

Two new mixed-ligand coordination polymers, {[Co(μ_1,3-sq)(H₂O)₂(2-Meim)₂]·2(2-Meim)}_n (1) and [Cd(μ_1,3-sq)(H₂O)₂(4(5)-Meim)₂]_n (2), (sq = squarate, 2-Meim = 2-methylimidazole, 4(5)-Meim = 5-methylimidazole) have been synthesized and structurally characterized by X-ray crystallography. The spectral (IR and UV–Vis) and thermal analyses are also reported. The Co(II) and Cd(II) ions are distorted octahedrally coordinated by four oxygen atoms of two O¹–O³-bridging squarate ligands and two trans-aqua ligands, and by two nitrogen atoms of the trans-imidazole (2-Meim or 4(5)-Meim) ligands. The structures of 1 and 2 consist of one-dimensional chains of μ-1,3-squarato bridged metal(II) complex units. These chains are held together by hydrogen bonding interactions, forming three-dimensional framework.     

Synthesis,structure and properties of some copper(II) complexes containing an ONO donor Schiff base and substituted imidazole ligands

Five new mixed ligand coper(II) complexes, viz. [Cu(SAA)(H₂O)] (1), [Cu(SAA)(MeImH)] (2), [Cu(SAA)(EtImH)] (3), [Cu(SAA)(BenzImH)] (4) and [Cu(SAA)(MebenzImH)] (5), where SAA = salicylideneanthranilic acid, MeImH = 2-methylimidazole, EtImH = 2-ethylimidazole, BenzImH = benzimidazole, MebenzImH = 2-methylbenzimidazole, have been synthesized and characterized by means of elemental analysis, FAB mass spectrometry, magnetic susceptibility, X-band EPR, electronic spectroscopy, IR and cyclic voltammetry. The frozen solution EPR spectra of the complexes have shown axial features. Single crystal X-ray analysis of 2 and 3 has revealed the presence of a distorted square planar geometry (N₂O₂) in the complexes. The superoxide dismutase (SOD) activity of the present complexes has also been measured and discussed.     

Synthesis, spectroscopic, thermal Studies, antimicrobial activities and crystal structures of Co(II), Ni(II), Cu(II) and Zn(II)-orotate complexes with 2-methylimidazole

The 2-methylimidazole complexes of Co(II), Ni(II), Cu(II) and Zn(II) orotates, mer-[Co(HOr)(H₂O)₂(2-meim)₂] (1), mer-[Ni(HOr)(H₂O)₂(2-meim)₂] (2), [Cu(HOr)(H₂O)₂(2-meim)] (3) and [Zn(HOr)(H₂O)₂(2-meim)] (4), were synthesized and characterized by elemental analysis, spectral (UV–Vis and FT-IR) methods, thermal analysis (TG, DTG and DTA), magnetic susceptibility, antimicrobial activity studies and single crystal X-ray diffraction technique. The complexes 1 and 2 have distorted octahedral geometries with two monodentate 2-methylimidazole and one bidentate orotate and two aqua ligands. The complexes 3 and 4 have distorted square pyramidal and trigonal bipyramidal geometry, respectively, with one 2-methylimidazole, bidentate orotate and aqua ligands. The orotate coordinated to the metal(II) ions through deprotonated nitrogen atom of pyrimidine ring and oxygen atom of carboxylate group as a bidentate ligand. The antimicrobial activities of 1 and 4 were found to be more active gram (+) than gram (−) and 4 could be use for treatment Staphylococcus aureus.     

Solvothermal syntheses and crystal structures of new Cu(II) complexes with phenylsuccinic acid

Five new Cu(II) complexes [Cu(psa)(phen)] · 3H₂O (1), [Cu(psa)(2bpy)] · 0.5H₂O (2), [Cu(psa)(2bpy)(H₂O)] · 3H₂O (3), [Cu(psa)(4bpy)] · H₂O (4), and [Cu(psa)_0.5(N₃)(2bpy)] (5) (H₂psa = phenylsuccinic acid, phen = 1,10-phenanthroline, 2bpy = 2,2′-bipyridine, and 4bpy = 4,4′-bipyridine) were obtained under solvothermal conditions and characterized by single-crystal X-ray diffraction. Complexes 2 and 3 were formed by one-pot reaction. In complex 2, Cu(II) ion is four-coordinated and locates at a slightly distorted square center. In complex 3, the coordinated water molecule occupies the axial site of Cu(II) ion forming a tetragonal pyramid geometry. Complexes 1 and 3 are of 1D chain structures, and extended into 2D supramolecular network by hydrogen bonds. Complex 2 is of zipper structure, and further assembled into 2D supramolecular network by hydrogen bonds and π–π stacking interactions. Complex 4 is a 3D CdSO₄-like structure with twofold interpenetration, while complex 5 is a dinuclear compound. The different structures of complexes 1–5 can be attributed to using the auxiliary ligands, indicating an important role of the auxiliary ligands in assembly and structure of the title complexes.     

Synthesis,structures and biological properties of nickel(II) phthalates with imidazole and its derivatives

Four new nickel(II) phthalate compounds: mononuclear complexes [Ni(Im)]₆(Pht)·H₂O (1), [Ni(Pht)(Im)₃(H₂O)₂]·H₂O (2) and [Ni(Pht)(2-MeIm)₃(H₂O)₃]·H₂O (3), and coordination polymer [Ni(Pht)(4-MeIm)₂(H₂O)]_n (4) (where Pht = dianion of o-phthalic acid, Im = imidazole, 2-MeIm = 2-methylimidazole, 4-MeIm = 4-methylimidazole) have been synthesized. The complexes 1–4 were characterised by elemental analysis, IR data, thermogravimetric, and X-ray diffraction analyses. X-ray analysis shows that the asymmetric unit of 1 consists of [Ni(Im)]₆²⁺ cation, Pht²⁻ anion and solvate H₂O molecule. The phthalate dianion does not take part in coordination to metal ion. The cations, anions and water molecules are linked via   N–H?$?$O and O–H?$?$O interactions forming 2D hydrogen-bonded networks. The structures of 2 and 3 are similar to other mononuclear Ni(II) phthalate complexes where Pht²⁻ anions act as monodentate ligands and uncoordinated carboxylate oxygen atoms participate in the formation of hydrogen bonded double-chains. The structure of 4 consists of [Ni(4-MeIm)₂(H₂O)] building units connected by phthalate ions to form helical chains. The complexes 1–4 were tested for their ability to increase the biosynthesis of enzymes.     

Self-assembly of 1D coordination polymers from nickel(II) tetraaza macrocycle and carboxylate ligands

Reactions of [Ni(L)]Cl₂ · 2H₂O (L = 3,14-dimethyl-2,6,13,17-tetraazatricyclo[14,4,0^1.18,0^7.12]docosane) with isophthalic acid (H₂isoph) and 1,3,5-cyclohexanetricarboxylic acid (H₃chtc) yield the 1D nickel(II) complexes {[Ni(L)(isoph)] · 3H₂O}_n (1) and {[Ni(L)(H-chtc)] · H₂O}_n (2). The structures were characterized by X-ray crystallography, spectroscopic and magnetic susceptibility. The crystal structures of the 1D chain compounds 1 and 2 show an elongated distorted octahedron about each nickel(II) ion. The magnetic behavior of two compounds exhibits weak intrachain antiferromagnetic interaction with J values of −0.93 cm⁻¹ for 1 and −1.28 cm⁻¹ for 2. The electronic spectra of the complexes are significantly affected by the nature of the carboxylate ligands.     

Three new pseudohalide bridged dinuclear Zn(II) Schiff base complexes: Synthesis,crystal structures and fluorescence studies

Three new dinuclear Zn(II) complexes [Zn(L)(μ_1,1-N₃)Zn(L)(N₃)] · 1.5H₂O (1), [Zn(L)(μ_1,1-NCO)Zn(L)(NCO)] · 1.5H₂O (2) and [Zn(L)(μ_1,1-NCS)Zn(L)(NCS)(OH₂)] (3) have been synthesized from a potentially tetradentate N₂O₂-donor Schiff base ligand LH, [LH = (OCH₃)(OH)C₆H₃CHN(CH₂)₂N(CH₃)₂], which is the condensation product of o-vanillin and 2-dimethylaminoethylamine. All the three complexes 1, 2 and 3 have been characterized by elemental analysis, IR and ¹H NMR spectroscopy, TGA and fluorescence studies. Finally, their structures have been established by the single crystal X-ray diffraction method. Structural studies reveal that in complexes 1, 2 and 3 the two Zn(II) centers are held together by a μ₂-phenolato oxygen atom and also by an end-on pseudohalide nitrogen (azide for 1; cyanate for 2; thiocyanate for 3) atom. Among the two deprotonated Schiff base ligands present in each complex, one acts as a tetradentate ligand (N₂O₂ donor set) while the other acts as a tridentate ligand (N₂O donor set), having a non-coordinated methoxy group. All the synthesized complexes display intraligand ¹(π–π^∗) fluorescence and can potentially serve as photoactive materials.     

One-dimensional and two-dimensional coordination polymers constructed from copper(II) nodes and polycarboxylato spacers: Synthesis,crystal structures and magnetic properties

Four new coordination polymers were obtained by employing polycarboxylato spacers and cationic copper(II) complexes as nodes: ^∞₂[Cu₃(trim)₂(NH₃)₆(H₂O)₃] (1); ^∞₁[Cu(tmen)(dhtp)] (2), ^∞₁[Cu(tmen)(hitp)(H₂O)] (3), ^∞₁[Cu(tmen)(nitp)] (4). (H₃trim = trimesic acid, H₂dhtp = 2,5-dihydroxy-terephthalic acid; H₂hitp = 5-hydroxy-isophthalic acid, H₂nitp = 5-nitro-isophthalic acid; tmen = N,N,N′,N′-tetramethyl-ethylenediamine). The crystal structures of the four compounds have been solved. Compound 1 consists of 2D coordination polymers with heart-shaped meshes, while compounds 2–4 contain infinite zigzag chains. The role of the hydrogen bond interactions in sustaining the supramolecular solid-state architectures in compounds 1 and 3 is discussed. The cryomagnetic investigation of compounds 1, 2, and 4 reveals antiferromagnetic interactions between the copper ions.     

Synthesis, crystal structure, spectroscopic and photoluminescence studies of manganese(II), cobalt(II), cadmium(II), zinc(II) and copper(II) complexes with a pyrazole derived Schiff base ligand

Varying coordination modes of the Schiff base ligand H₂L [5-methyl-1-H-pyrazole-3-carboxylic acid (1-pyridin-2-yl-ethylidene)-hydrazide] towards different metal centers are reported with the syntheses and characterization of four mononuclear Mn(II), Co(II), Cd(II) and Zn(II) complexes, [Mn(H₂L)(H₂O)₂](ClO₄)₂(MeOH) (1), [Co(H₂L)(NCS)₂] (2), [Cd(H₂L)(H₂O)₂](ClO₄)₂ (3) and [Zn(H₂L)(H₂O)₂](ClO₄)₂ (4), and a binuclear Cu(II) complex, [Cu₂(L)₂](ClO₄)₂ (5). In the complexes 1-4 the neutral ligand serves as a 3N,2O donor where the pyridine ring N, two azomethine N and two carbohydrazine oxygen atoms are coordinatively active, leaving the pyrazole-N atoms inactive. In the case of complex 5, each ligand molecule behaves as a 4N,O donor utilizing the pyridine N, one azomethine N, the nitrogen atom proximal to the azomethine of the remaining pendant arm and one pyrazole-N atom to one metal center and the carbohydrazide oxygen atom to the second metal center. The complexes 1-4 are pentagonal bipyramidal in geometry. In each case, the ligand molecule spans the equatorial plane while the apical positions are occupied by water molecules in 1, 3 and 4 and two N bonded thiocyanate ions in 2. In complex 5, the two Cu(II) centers have almost square pyramidal geometry (τ = 0.05 for Cu1 and 0.013 for Cu2). Four N atoms from a ligand molecule form the basal plane and the carbohydrazide oxygen atom of a second ligand molecule sits in the apex of the square pyramid. All the complexes have been X-ray crystallographically characterized. The Zn(II) and Cd(II) complexes show considerable fluorescence emission while the remaining complexes and the ligand molecule are fluorescent silent.     

Preparation,crystal structures and spectroscopic characterization of oxalate copper(II) complexes containing the nitrogen ligands 4,4′-dimethyl-2,2′-bipyridine and di(2-pyridyl)sulfide

The preparation, crystal structures and spectroscopic characterization of four oxalate copper(II) complexes containing the 4,4′-dimethyl-2,2′-bipyridine (Mebpy) or di(2-pyridyl)sulfide (DPS) nitrogen ligands namely [μ-(ox){Cu(Mebpy)(NO₃)(H₂O)}₂] (1), [μ-(ox){Cu(Mebpy)(ClO₄)(H₂O)}₂] (2), [μ-(ox){Cu(DPS)(H₂O)}₂](ClO₄)₂ (3) and [Cu(DPS)(ox)(H₂O)] · 2H₂O (4) are described. X-ray diffraction measurements have shown that complexes 1–3 are binuclear, in which the oxalate anion bridges two Cu(II) centers, while the complex (4) is mononuclear and the oxalate anion adopts the terminal bidentate chelating coordination mode. In 1 and 2 the Cu(II) sites display a distorted octahedral geometry (4+2 environment) and in compounds 3 and 4 the Cu(II) centers exhibit a slightly distorted square pyramidal geometry. In addition, complexes 1 and 2 present a 2D supramolecular arrangement through hydrogen bonds between coordination water molecules and nitrate or perchlorate anions and π-stacking interaction between the pyridyl rings of Mebpy nitrogen ligands.     

A seven membered chelate ring complex of Mn(II) derived from bis(5-phenyl-2H-1,2,4-triazole)-3-yl-disulfane and cleavage of the S-S bond in a Co(II) complex: Synthesis, spectral and structural characterization

The reaction of Mn(OAc)₂·4H₂O with bis(5-phenyl-2H-1,2,4-triazole)-3-yl-disulfane (H₂ptds·2H₂O) (1) yielded new complex [Mn(ptds)(o-phen)₂] (2). It is observed that under similar conditions the reaction of Co(OAc)₂ with H₂ptds·2H₂O (1) leads to thermolysis of the S-S bond of the disulfane to yield [Co(pts)(o-phen)₂]·H₂O·0.5C₂H₅OH, with the newly generated organic ligand 5-phenyl-2H-1,2,4-triazole-3-sulfinate, (pts)²⁻. The ligand H₂ptds·2H₂O (1), [Mn(ptds)(o-phen)₂] (2) and [Co(pts)(o-phen)₂]·H₂O·0.5C₂H₅OH (3) crystallized into monoclinic, trigonal and triclinic crystal systems, respectively. The triazole ring nitrogen of the bidentate ligand chelates the Mn(II) center forming a seven membered chelate ring, while N, O donor sites of the resulting triazole sulfinate bond Co(II) to form a five membered chelate. The resulting complexes are paramagnetic and have a distorted octahedral geometry.     

Assembling of copper(II) dipicolinate complexes

The role of ancillary ligands, namely imidazole (im), pyridine (py), 2,2′-bipyridine (bpy) and 1,10-phenanthroline (phen) in the assembly of copper(II) dipicolinate complexes are presented. Mononuclear complexes are observed in the case of monodentate ligands. The mononuclear complex [Cu(im)₃L]·4H₂O (1) (L = dipicolinate anion) has a distorted octahedral structure with Z′ = 2, whereas [CuL(py)(H₂O)]·2H₂O (2) adopts distorted square pyramidal geometry. The bidentate ligands bpy and phen favor the formation of dinuclear complexes. The dinuclear complex [CuL(bpy)(μ-L)Cu(bpy)(H₂O)]·9H₂O (3) has one carbonyl oxygen atom of a carboxylate group of dipicolinate acting as a bridging ligand to the copper site that is devoid of a coordinated water molecule. The complex has an angle of 83.55° between the plane of L and bpy attached to one copper site, whereas it has an angle of 78.13° between the plane L and bpy attached to the other copper site. A 1,10-phenanthroline containing dinuclear copper(II) dipicolinate complex, [Cu(phen)(H₂O)(μ-L)Cu(phen)₂][CuL₂]·12H₂O (4), has been structurally characterized. It has an unusual carboxylate bridge.     

Synthesis and characterization of coordination polymers of a carboxylato cyclophane with metal [Zn(II) and Cd(II)]-2,2′-bipyridines

N,N′,N′′,N′′′-Tetrakis(3-carboxy-propionyl)-1,6,20,25-tetraaza-[6.1.6.1] paracyclophane, H₄cp has been complexed with metal (Zn(II) and Cd(II)) 2,2′-bipyridyls. The resulting complexes of the composition [{Zn(2,2′-bpy)}₂(cp)]_n·4H₂O 1 and [{Cd(2,2′-bpy)}₂(cp)]_n·5H₂O 2 (2,2′-bpy = 2,2′-bipyridine) have been characterized using spectroscopic (IR, solid state UV–Vis), elemental analysis and single-crystal X-ray diffraction measurements. In these complexes the cyclophane coordinates in different modes, and in complex 2, Cd(II) is hepta-coordinated. However, under harsh reaction conditions (using excess nitric acid and a longer reaction time) debranching of the cyclophane is observed in the reaction of Zn(2,2′-bpy)(NO₃)₂ with H₄cp, and a complex of the composition [Zn(2,2′-bpy)(Suc)]_n3 (suc = succinate) is isolated. Using non-covalent interactions, complexes 1 and 2 provide 3D supramolecular structures, whereas an infinite 1D chain structure is observed for complex 3. The thermal and photoluminescence properties of the complexes have also been studied.     

Salen-type nickel(II), palladium(II) and copper(II) complexes having chiral and racemic camphoric diamine components

Chiral and racemic Salen-type Schiff-base ligands (H₂L¹, H₂L² and H₂L³), condensed between D-(+)- and D,L-camphoric diamine (also known as (1R,3S)-1,2,2-trimethylcyclopentane-1,3-diamine) and 2-hydroxybenzaldehyde or 3,5-dibromo-2-hydroxybenzaldehyde with a 1:2 molar ratio, have been synthesized and characterized. A series of new nickel(II), palladium(II) and copper(II) complexes of these chiral and racemic ligands exhibiting different coordination number (4, 5 and 6) have been characterized with the formulae [NiL¹]·CH₃OH (3), [NiL¹]·H₂O (4), [NiL²] (5), [PdL²] (6), [Cu₂(L²)₂(H₂O)] (7) and [NiL³(DMF)(H₂O)] (8). Different solvent molecules in 3 and 4 (methanol and water molecules) as well as different apical ligands in 7 and 8 (water and DMF molecules) are involved in different O–H···O hydrogen bonding interactions to further stabilize the structures. UV–Vis (UV–Vis), circular dichroism (CD) spectra and thermogravimetric (TG) analyses for the metal complexes have also been carried out.     

Co(II), Mn(II) and Cu(II) complexes of fluoroquinolones: Synthesis, spectroscopical studies and biological evaluation against Trypanosoma cruzi

[MnCl₂(NOR)(H₂O)₂] (1), [MnCl₂(SPAR)(H₂O)₂] (2), [CoCl₂(NOR)(H₂O)₂] (3) [CoCl₂(SPAR)(H₂O)₂] (4), [CuCl₂(phen)(NOR)] (5) and [CuCl₂(phen)(SPAR)] (6) complexes with norfloxacin (NOR) and sparfloxacin (SPAR) were obtained from MnCl₂·4H₂O, CoCl₂·4H₂O and CuCl₂(phen). In all cases the NOR and SPAR coordinate in the neutral zwitterionic form. The electron paramagnetic resonance spectra of the Cu(II) complexes (5) and (6) in aqueous and DMSO solutions indicate mixture of mononuclear and binuclear complex. Complexes (1-6), together with the corresponding ligands were evaluated for their in vitro trypanocidal effect, against both bloodstream trypomastigotes and intracellular forms of Trypanosoma cruzi. SPAR and NOR were poorly effective upon T. cruzi, complexes (3) and (4) were active against intracellular forms of the parasite. The complexes (5) and (6) displayed a higher activity upon both bloodstream and intracellular forms. The potency of fluoroquinolones, specially those coordinated to Cu(II)-phen justify further trypanocidal screening assays with this compounds in vitro as well as upon experimental models of T. cruzi infection.     

Subtle role of counteranions in molecular construction: Structures and properties of novel Cu(II) coordination complexes with bis-(1-benzoimidazolymethylene)-(2,5-thiadiazoly)-disulfide

The direct self-assembly of bis-(1-benzoimidazolymethylene)-(2,5-thiadiazoly)-disulfide (L) with CuSO₄, Cu(NO₃)₂ and CuCl₂ affords three novel supramolecular complexes: 1-D ladder-like chain complex {[Cu(SO₄)(L)] · (CH₃OH)}_n (1), dimer complexes {[Cu(L)(CH₃O)]₂(NO₃)₂} · 2H₂O (2) and [Cu(L)(Cl)(N₃)]₂ · 2CH₃OH (3). The nature of the anions is the underlying reason behind the differences in the structures of this series of complexes. Furthermore, utilizing the coordinatively unsaturated complexes 2 and 3 as precursor complexes, two new derivative complexes [Cu(L)(NCS)(CH₃O)]₂ · 2CH₃OH (2A) and [Cu(L)(ClO₄)(N₃)]₂ · 2CH₃OH (3A) are obtained by the addition and exchange reactions of complexes 2 and 3 with anions. X-ray crystallographic analysis shows that the two derivatives retain the skeletons of their precursor complexes, and the anions with the stronger coordination capacity only bind to the active position of precursor complexes. In addition, different from the obvious effects on the structures in the direct self-assembly of the metal and ligand, the change of counteranions has no great impact on the structures in the anion exchange reactions. We also study the catalytic activities of the complexes 2, 2A, 3, and 3A, which have similar skeletons, for the oxidative coupling polymerization of 2,6-dimethylphenol (DMP). And we find that the introductions of different coordination counterions produce significant impacts on the catalytic properties of these complexes.     

Transition metal complexes with thiosemicarbazide-based ligands. Part LIV. Nickel(II) complexes with pyridoxal semi- (PLSC) and thiosemicarbazone (PLTSC). Crystal and molecular structure of [Ni(PLSC)(H2O)3](NO3)2 and [Ni(PLTSC-H)py]NO3

This paper describes the synthesis of the first Ni(II) complexes with pyridoxal semicarbazone (PLSC), viz. Ni(PLSC)Cl₂ · 3.5H₂O (1), [Ni(PLSC)(H₂O)₃](NO₃)₂ (2), Ni(PLSC)(NCS)₂ · 4H₂O (3), [Ni(PLSC-2H)NH₃] · 1.5H₂O (4), as well as two new complexes with pyridoxal thiosemicarbazone (PLTSC), [Ni(PLTSC-H)py]NO₃ (5) and [Ni(PLTSC-H)NCS] (6). Complexes 1–3 are paramagnetic and have most probably an octahedral structure, for complex 2 this was proved by X-ray diffraction analysis. In contrast, complexes 4–6 are diamagnetic and have a square-planar structure, and in the case of complex 5 this was also confirmed by X-ray structural analysis. In all cases the Schiff bases are coordinated as tridentate ligands with an ONX (X = O, PLSC; X = S, PLTSC) set of donor atoms. With the complexes involving the neutral form of PLSC and the monoanionic form of PLTSC, the PL moiety is in the form of a zwitterion. In addition to the above-mentioned techniques, all the complexes were characterized by measuring their molar conductivities, UV–Vis and partial IR spectra.     

Ni(II) and Cu(II) complexes of phenoxy-ketimine ligands: Synthesis,structures and their utility in bulk ring-opening polymerization (ROP) of l-lactide

Synthetic, structural and catalysis studies of Ni(II) and Cu(II) complexes of a series of phenoxy-ketimine ligands with controlled variations of sterics, namely 2-[1-(2,6-diethylphenylimino)ethyl]phenol (1a), 2-[1-(2,6-dimethylphenylimino)ethyl]phenol (1b) and 2-[1-(2-methylphenylimino)ethyl]phenol (1c), are reported. Specifically, the ligands 1a, 1b and 1c were synthesized by the TiCl₄ mediated condensation reactions of the respective anilines with o-hydroxyacetophenone in 21–23% yield. The nickel complexes, {2-[1-(2,6-diethylphenylimino)ethyl]phenoxy}₂Ni(II) (2a) and {2-[1-(2,6-dimethylphenylimino)ethyl]phenoxy}₂Ni(II) (2b), were synthesized by the reaction of the respective ligands 1a and 1b with Ni(OAc)₂ · 4H₂O in the presence of NEt₃ as a base in 71–75% yield. The copper complexes, {2-[1-(2,6-diethylphenylimino)ethyl]phenoxy}₂Cu(II) (3a), {2-[1-(2,6-dimethylphenylimino)ethyl]phenoxy}₂Cu(II) (3b) and {2-[1-(2-methylphenylimino)ethyl]phenoxy}₂Cu(II) (3c) were synthesized analogously by the reactions of the ligands 1a, 1b and 1c with Cu(OAc)₂ · H₂O in 70–87% yield. The molecular structures of the nickel and copper complexes 2a, 2b, 3a, 3b and 3c have been determined by X-ray diffraction studies. Structural comparisons revealed that the nickel centers in 2a and 2b are in square planar geometries while the geometry around the copper varied from being square planar in 3a and 3c to distorted square planar in 3b. The catalysis studies revealed that while the copper complexes 3a, 3b and 3c efficiently catalyze ring-opening polymerization (ROP) of l-lactide at elevated temperatures under solvent-free melt conditions, producing polylactide polymers of moderate molecular weights with narrow molecular weight distributions, the nickel counterparts 2a and 2b failed to yield the polylactide polymer.     

Synthesis, structure and magnetic properties of cobalt(II) and copper(II) coordination polymers assembled by phthalate and 4-methylimidazole

New coordination polymers [M(Pht)(4-MeIm)₂(H₂O)]_n (M=Co (1), Cu (2); Pht²⁻=dianion of o-phthalic acid; 4-MeIm=4-methylimidazole) have been synthesized and characterized by IR spectroscopy, X-ray crystallography, thermogravimetric analysis and magnetic measurements. The crystal structures of 1 and 2 are isostructural and consist of [M(4-MeIm)₂(H₂O)] building units linked in infinite 1D helical chains by 1,6-bridging phthalate ions which also act as chelating ligands through two O atoms from one carboxylate group in the case of 1. In complex 1, each Co(II) atom adopts a distorted octahedral N₂O₄ geometry being coordinated by two N atoms from two 4-MeIm, three O atoms of two phthalate residues and one O atom of a water molecule, whereas the square-pyramidal N₂O₃ coordination of the Cu(II) atom in 2 includes two N atoms of N-containing ligands, two O atoms of two carboxylate groups from different Pht, and a water molecule. An additional strong O-H?O hydrogen bond between a carboxylate group of the phthalate ligand and a coordinated water molecule join the 1D helical chains to form a 2D network in both compounds. The thermal dependences of the magnetic susceptibilities of the polymeric helical Co(II) chain compound 1 were simulated within the temperature range 20-300 K as a single ion case, whereas for the Cu(II) compound 2, the simulations between 25 and 300 K, were made for a linear chain using the Bonner-Fisher approximation. Modelling the experimental data of compound 1 with MAGPACK resulted in: g=2.6, |D|=62 cm⁻¹. Calculations using the Bonner-Fisher approximation gave the following result for compound 2: g=2.18, J=-0.4 cm⁻¹.