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The reaction of equimolar amounts of Ni(NO3)2·6H2O, Na2(suc)·6H2O (suc = succinate) and 4,4′-bipyridine (bipy) under different conditions yield the coordination polymers [Ni(suc)(bipy)(H2O)2]n·2nH2O (1) and [Ni(suc)(bipy)(H2O)2]n·nH2O (2). The complexes were characterized by elemental analysis, spectroscopic, thermogravimetric, and magnetic susceptibility measurements. Crystal structures reveal that the metal centers in both complexes are in a distorted octahedral N2O4 coordination sphere assembled by mutually trans pairs of 4,4′-bipyridine, succinate, and water molecules. The helical metal–succinate chains have a right-handed sixfold configuration in 1, with guest water molecules inside the helix, and both right- and left-handed fourfold configurations in 2, with guest water molecules outside the helix. The parallel helical substructures are connected by 4,4′-bipyridine and provide 3D chiral 75.9 and achiral 65.8 networks in 1 and 2, respectively.

The synthesis and physical properties of bis(2-(1H-imidazol-2-yl)-pyridine)copper(II) with chloride, nitrate and perchlorate as counteranions have been described. Microanalysis, magnetic susceptibility, conductivity and various spectroscopic measurements have been used for the characterization of the complexes. The crystal structures of all three complexes have been determined. Intermolecular hydrogen-bonding interactions and the resulting self-assembly patterns for each of the species have been scrutinized. The chloride containing complex crystallizes as a trihydrate, where the metal ion is in a tetragonally elongated cis-N4Cl2 coordination sphere. This complex provides a three-dimensional honeycomb-like structure through N–H⋯Cl, O–H⋯Cl and O–H⋯O hydrogen bonds. In the nitrate containing species, one of the two counteranions coordinates to the metal centre to provide an irregular N4O2 coordination sphere, while the other counteranion, with the help of a lattice water molecule, assembles a ladder-like structure via N–H⋯O and bifurcated O–H⋯O,O hydrogen bonds. A one-dimensional polymeric species has been formed when perchlorate is the counteranion. Here one of the two perchlorates acts as a bridge between the metal centres that are in tetragonally elongated trans-N4O2 coordination spheres. This polymeric chain, together with the second perchlorate and a water molecule, form a ribbon-like structure due to N–H⋯O and O–H⋯O hydrogen bonds.

A series of copper(II) complexes having the formula [Cu( n - R -pyp)X] with the N,N,O-donor Schiff base system 2- N -(picolinylidene)- n - R -phenol ( n - R -Hpyp) (where n = 3, 4, 5 and 6, when R = Me and n = 4 when R = Cl) and halide (X − = Cl − or Br − ) as an ancillary ligand have been synthesized. The complexes are characterized by microanalytical, magnetic and various spectroscopic measurements. They display solvatochromic behavior. Single crystal X-ray structures of all the complexes are determined. In coordinatively unsaturated species such as a square–planar complex, the metal ion can interact with a fifth atom and if this atom is metal bound, dimeric or polymeric aggregate is formed. In the present series of complexes, the metal ions are square–planar and distorted square–pyramidal when there is an intermolecular Cu···X interaction. In addition to this Cu···X interaction, presence of intermolecular weak non-covalent interactions namely O–H···O, C–H···O, C–H···X and π···π are perceived. The supramolecular architectures formed by the molecules of these complexes via these interactions are scrutinized. The observed supramolecular structural motifs can be classified as staircase, ladder, brick-wall and square-grid. Except for R = Cl the analogous chloride and bromide coordinated complexes show similar structural features.

Copper(II) complexes having the general formula [Cu(Ln)2] with the N,O-donor reduced Schiff bases N-(2-hydroxy-5-X-benzyl)-(R)-α-methylbenzylamine and N-(2-hydroxy-5-X-benzyl)-(S)-α-methylbenzylamine (X = Cl and Br) (HLn) are described. These chiral complexes crystallize in the noncentrosymmetric P212121 (X = Cl) and P21 (X = Br) space groups. In each case, self-assembly via intermolecular C–H⋯O interaction leads to a supramolecular helical superstructure.

Two ternary copper(II) complexes having the general formula [Cu(pyp)X] with the tridentate Schiff base 2-N-(picolinylidene)phenol (Hpyp) and halide (X- = Cl-, Br-) as the ancillary ligand have been synthesized and characterized. Both complexes exhibit solvatomorphism due to cocrystallization with different solvent molecules. Two cases have been investigated: (i) the dihydrated species [Cu(pyp)Cl]·2H2O (1) and [Cu(pyp)Br]·2H2O (2), isolated by slow evaporation of aqueous methanol solution of the complexes, and (ii) the corresponding monomethanolic forms [Cu(pyp)Cl]·CH3OH (3) and [Cu(pyp)Br]·CH3OH (4), obtained by crystallization of 1 and 2 from dry methanol. To investigate the crystal compositions and packing features, single-crystal X-ray diffraction measurements as well as thermogravimetric and differential scanning calorimetric measurements have been carried out. In the context of structural features, the hydrated forms and also the monomethanolic forms are isomorphic. The dihydrated form shows a zippe...

Reactions of Li2[PdCl4] with N-(aroyl)-N′-(2,4-dimethoxybenzylidene)hydrazines (H2L = (4-R–C6H4)C( O)NHN CH(2,4-(CH3O)2C6H3)) in presence of PPh3 have provided cyclopalladated complexes having the general formula [PdL(PPh3)] (1, 2 and 3 where R = OCH3, CH3 and Cl, respectively) and a coordination complex trans-[Pd(HL)(PPh3)2Cl] (4 where R = NO2). The complexes have been characterized by elemental analysis, infrared, 1H NMR and electronic absorption spectroscopy. X-ray structures of all the complexes have been determined. In 1, 2 and 3, the C,N,O-donor dianionic ligand (L2−) forms two fused five-membered chelate rings at the metal centre. On the other hand, the monoanionic ligand (HL−) acts as deprotonated amide N-donor in 4. The strong electron withdrawing effect of the nitro group on the aroyl fragment is possibly responsible for the monodentate amide N-coordinating behavior of HL− in 4. The orientation of the 4-methoxy group in 1 is different than that in 2 and 3 due to intramolecular C–H⋯π interaction in the last two complexes. The structure of 4 shows an apical C–H⋯Pd interaction involving the azomethine (–CH N–) group of HL−. In the crystal lattice of all the structures, various types of intermolecular non-covalent interactions are present. The self-assembly of the molecules of 1, 2 and 3 leads to two-dimensional networks. The same network observed for 2 and 3 reflects the interchangeability of the chloro and methyl groups due to their similar volumes. In the case of 4, the complex and the water molecules present in the crystal lattice form parallel homo-chiral helices and finally interhelical interactions lead to a three-dimensional network.

Three ternary copper(II) complexes of general formula [Cu(bhac)(hc)], with a tridentate Schiff base, acetylacetone benzoylhydrazone (H2bhac) and monodentate N-heterocycles (hc=pyrazole, imidazole and pyridine), have been synthesized. Elemental analysis, various forms of spectroscopy (infrared, electronic absorption and EPR), cyclic voltammetry, cryomagnetic measurements and X-ray crystallography were used for the characterization of the complexes. Analytical data, infrared and electronic spectral features and molar conductivity values are consistent with the proposed molecular formulae and the +2 oxidation state of the metal ion in these complexes. In each complex, the enolate-O, the imine-N and the deprotonated amide-O donor tridentate ligand (bhac2−) and the sp2 N donor heterocycle form an O2N2 square-plane around the metal ion. The whole molecule of none of the complexes is perfectly planar because of different orientation of the phenyl ring plane of the tridentate ligand and that of the heterocycle ring plane with respect to the plane containing rest of the molecule. In the solid state, the complexes having the pyrazole and the pyridine as the heterocyclic ligand, exist as centrosymmetric dimeric species due to very weak apical coordination of the metal bound enolate-O. The complex of imidazole has no such apical coordination and exists as a monomer. In the crystal lattice, the molecules of these complexes are involved in a variety of intermolecular non-covalent interactions such as O–H⋯O, N–H⋯O, N–H⋯N, C–H⋯π and π⋯π. Self-assembly via these interactions lead to a one-dimensional arrangement of [Cu(bhac)(Hpyrz)]·C2H5OH, a two-dimensional layered structure of [Cu(bhac)(Himdz)] and a three-dimensional network of [Cu(bhac)(py)]. Cryomagnetic and EPR spectral measurements indicates weak antiferromagnetic spin-exchange in all the three complexes.

Cyclopalladated complexes with the Schiff base N-(benzoyl)-N′-(2,4-dimethoxybenzylidene)hydrazine (H2L, 1) have been described. The reaction of 1 with Li2[PdCl4] in methanol yields the complex [Pd(HL)Cl] (2). [Pd(HL)(CH3CN)Cl] (3) has been prepared by dissolving 2 in acetonitrile. In methanol–acetonitrile mixture, treatment of 2 with two mole equivalents of PPh3 produces [PdL(PPh3)] (4) and that with one mole equivalent of PPh3 produces [Pd(HL)(PPh3)Cl] (5). Crystallization of 2 from dmso-d6 results into isolation of [Pd(HL)((CD3)2SO)Cl] (6). In 2, the monoanionic ligand (HL−) is C,N,O-donor and the Cl-atom is trans to the azomethine N-atom. In 3, 5 and 6, HL− is C,N-donor and the Cl-atom is trans to the metallated C-atom. The remaining fourth coordination site is occupied by the N-atom of CH3CN, the P-atom of PPh3 and the S-atom of (CD3)2SO in 3, 5 and 6, respectively. Thus on dissolution in acetonitrile and dmso and in reaction with stoichiometric PPh3 the incoming ligand imposes a rearrangement of the coordinating atoms on the palladium centre. On the other hand, in presence of excess PPh3 deprotonation of the amide functionality in 2 occurs and the Cl-atom is replaced by the P-atom of PPh3 to form 4. Here the dianionic ligand (L2−) remains C,N,O-donor as in 2. The compounds have been characterized with the help of elemental analysis (C, H, N), infrared, 1H NMR and electronic absorption spectroscopy. Molecular structures of 3, 4, and 6 have been determined by X-ray crystallography.