Satyanarayan Pal

A one-dimensional assembly of a square-planar copper(II) complex with alternating short and long Cu⋯Cu distances. Metal ion spin-exchange viaπ-π interactions

A mixed-ligand copper(II) complex, [Cu(bhac)(Hdmpz)], with a tridentate Schiff base, acetylacetone benzoylhydrazone (H2bhac) and a monodentate heterocycle, 3,5-dimethylpyrazole (Hdmpz), has been synthesized and characterized by analytical, infrared and electronic absorption spectroscopy, and cyclic voltammetry. The molecular structure of the complex has been determined by X-ray crystallography. The metal ion is coordinated to the enolate-O, the imine-N and the deprotonated amide-O centres of the deprotonated Schiff base (bhac2−) and to the sp2 N atom of Hdmpz. The coordination geometry around the metal centre is square-planar. There is no displacement of the metal centre from the N2O2 square plane. The whole molecule is essentially planar, barring a small variation in the orientation of the Hdmpz plane with respect to the {Cu(bhac)} plane. In the solid state, two types of π-π interactions on two sides of [Cu(bhac)(Hdmpz)] molecule lead to a one-dimensional arrangement of the complex with sequential short [3.5952(8) A] and long ([5.5960(12) A] Cu⋯Cu distances. Solid state as well as frozen solution EPR spectral measurements reveal an antiferromagnetically coupled dicopper(II) system and indicate a magnetic exchange interaction mediated by π-π interactions. Magnetic susceptibility data in the temperature range of 10–300 K are consistent with this observation. The magnitude of the coupling constant J, obtained by least-squares fitting of the data using the Bleany–Bowers expression, is −6.0(1) cm−1.

Square-planar nickel(II) complexes with a tridentate Schiff base and monodentate heterocycles: self-assembly to dimeric and one-dimensional array via hydrogen bonding

Abstract Two nickel(II) complexes having the general formula [Ni(bhac)L] with tridentate ONO-donor acetylacetone benzoylhydrazone (H2bhac) and monodentate N-donor heterocycles (L=3,5-dimethylpyrazole (Hdmpz) and imidazole (Himdz)) are reported. The complexes were synthesized in ethanol media by reacting Ni(O2CCH3)2·4H2O, H2bhac and L in 1:1:1 mole ratio and characterized by analytical, magnetic and spectroscopic methods. X-ray crystal structures of both complexes have been determined. In each complex, the metal ion is in square-planar N2O2 coordination geometry. In the solid state, a one-dimensional assembly of the [Ni(bhac)(Himdz)] molecules is formed via intermolecular hydrogen bonds between the imidazole N–H groups and the uncoordinated N-atoms of the deprotonated amide functionalities. On the other hand, two [Ni(bhac)(Hdmpz)] molecules are involved in a pair of complementary hydrogen bonds between the pyrazole N–H groups and the coordinated O-atoms of the deprotonated amide functionalities forming a dinuclear species.

Copper(II)-activated transformation of azomethine to imidate: synthetic and structural studies

Abstract The Schiff base 2-pyridine–carboxaldehyde 4-dimethylaminobenzoylhydrazone (HL, 1) was prepared by reacting 2-pyridine–carboxaldehyde and 4-dimethylaminobenzoylhydrazine in a 1:1 molar ratio in methanol. Reaction of HL (1) with Cu(O2CCH3)2·H2O (in a 1:1 molar ratio) in methanol afforded a dinuclear copper(II) complex, [Cu2(μ-O2CCH3)2L′2]·2H2O (2). The azomethine functionality (CHN) of 1 is converted to imidate (C(OMe)N) in the complexed ligand L′−. Molecular structures of both 1 and 2 were determined by X-ray crystallographic studies. The dinuclear molecule of 2 is centrosymmetric and contains two monoatomic bridging acetate groups. Each copper(II) centre is in a square-pyramidal N2O3 coordination sphere. The ligand, L′− coordinates the metal ion via the pyridine-N, the imidate-N, and the deprotonated amide-O atoms. One of the acetate oxygen atoms completes the N2O2 square-plane. The oxygen of the symmetry-related acetate fills the apical coordination site. Structural parameters are consistent with both copper ions being in a +2 oxidation state. The room temperature magnetic moment is 1.89 μB (per Cu). In powder phase the complex displays an axial EPR spectrum at 298 K. The complex is nonconducting in methanol solution. The electronic spectrum shows a ligand field absorption at 680 nm and charge transfer bands in the range 426–215 nm.

Mononuclear Pervanadyl (VO2+) Complexes with Tridentate Schiff Bases: Self-assemblingvia C-H…oxo and π-π Interactions

Pervanadyl (VO2+) complexes with N-(aroyl)-N′-(picolinylidene)hydrazines (HL = Hpabh, Hpath and Hpadh; H stands for the dissociable amide hydrogen) are described. The Schiff bases were obtained by condensation of 2-pyridine-carboxaldehyde with benzhydrazide (Hpabh), 4-methylbenzhydrazide (Hpath) and 4-dimethylaminobenzhydrazide (Hpadh), respectively. The reaction of [VO(acac)2] and HL in acetonitrile in air affords the complexes of general formula [VO2L]. The diamagnetic nature and EPR silence confirm the +5 oxidation state of vanadium in these complexes. Infrared spectra of the complexes are consistent with the enolate form of the coordinated ligands. Electronic spectra show charge transfer bands in the range 486–233 nm. The complexes are redox active and display an irreversible reduction (–0.64 to –0.72 V vs. Ag/AgCl). The crystal structures of all the complexes have been determined. In each complex, the metal centre is in a distorted trigonal-bipyramidal N2O3 coordination sphere formed by the pyridine-N, the imine-N and the deprotonated amide-O donor L– and two oxo groups. The planar ligand satisfies one equatorial and two axial positions. The other two equatorial positions are occupied by the two oxo groups. In the solid state, the molecules of each of the three complexes form a chain-like arrangement via the azomethine-H…oxo interactions. Interchain weak π-π interactions lead to two dimensional networks for [VO2(pabh)] and [VO2(path)]. On the other hand, [VO2(padh)] forms a two-dimensional network through interchain N-methyl-H…oxo interactions. Mononukleare Pervanadyl(VO2+)-Komplexe mit dreizahnigen Schiffschen Basen: Strukturaufbau via C–H…oxo- und π-π-Wechselwirkungen Pervanadyl(VO2+)-Komplexe mit N-(aroyl)- N′-(picolinyiden)hydrazinen (HL = Hpabh, Hpath und Hpadh; H steht fur abdissoziierbaren Amidwasserstoff) werden beschrieben. Die Schiffschen Basen wurden durch Kondensationsreaktionen von 2-Pyridincarboxylaldehyd mit Benzhydrazid (Hpabh), 4-Methylbenzhydrazid (Hpath) bzw. 4-Dimethylaminobenzhydrazid (Hpadh) erhalten. Die Reaktion von [VO(acac)2] und HL in Acetonitril an Luft ergibt die Komplexe der allgemeinen Formel [VO2L]. Die diamagnetische Natur und fehlende EPR-Signale bestatigen den Oxidationszustand +5 des Vanadiums in diesen Komplexen. Die IR-Spektren der Komplexe stehen in Ubereinstimmung mit der Enolat-Form der Liganden. Die Elektronenspektren zeigen Chargetransfer-Banden im Bereich von 486 bis 233 nm. Die Komplexe sind redox-aktiv und zeigen eine irreversible Reduktion (–0,64 bis –0,72 V vs. Ag/AgCl). Die Kristallstrukturen aller Verbindungen wurden bestimmt. In jedem Komplex liegt das Metallatom in einer verzerrt-trigonal-pyramidalen N2O3-Koordinationssphare vor, die aus dem Pyridin-N-Atom, dem Imin-N-Atom und dem deprotonierten Amid-O-Atom des Donors L– und zweier Oxogruppen gebildet wird. Die planaren Liganden besetzen eine aquatoriale und zwei axiale Positionen. Die anderen zwei aquatorialen Positionen werden durch die zwei Oxogruppen besetzt. Im festen Zustand bilden die Molekule der drei Komplexe eine kettenartige Anordnung uber die Azomethin-H…Oxo-Wechselwirkungen. Schwache π-π-Wechselwirkungen zwischen den Ketten fuhren zu einem zweidimensionalen Netz bei [VO2(pabh)] und [VO2(path)]. [VO2(padh)] bildet eine zweidimensionale Struktur durch N-Methyl-H…Oxo-Wechselwirkungen.

A one-dimensional assembly of copper(II) polyhedra via dual use of hydrogen-bonding and π–π interaction

Abstract A copper(II) complex [Cu(Hpadh)Cl2] with pyridine-N, imine-N and amide-O coordinating 2-pyridine-carboxaldehyde 4-dimethylaminobenzoylhydrazone (Hpadh) has been synthesized and structurally characterized. In the solid state, each square–pyramidal Cu(Hpadh)Cl2 unit is connected to one neighbour by a pair of hydrogen bonds between the amide-H and the apical chloride and to the other by a couple of π–π interactions between the aromatic rings of the coordinated ligands forming a novel chain-like arrangement of copper(II) centres with successive long and short Cu···Cu distances. Variable temperature (300–18 K) magnetic susceptibility measurements showed that the complex is essentially Curie paramagnetic.

Silver(I) helicates with 2-(arylazo)pyrimidines. Single crystal X-ray structure of {2-(phenylazo)pyrimidine}silver(I) nitrate

Abstract 2-(Arylazo)pyrimidines (aapm) react with AgNO3 in methanol and crystallises in a single strand right-handed helical coordination polymer, [Ag(aapm)(NO3)]n. The X-ray structure determination of Ag[2-(phenylazo)pyrimidine] (papm) (NO3) (abbreviated, Ag(papm)(NO3)) suggests the triangular coordination around Ag(I) which is made up of chelated azoimine, –NN–CN–, function from one ligand and the third donor centre is coming from meta-related pyrimidine-N of the adjacent papm of the second Ag(papm)-unit. The coordination polymer is propagated through pyrimidine-N→Ag bonding.

Syntheses, structures and properties of trans-dichlororuthenium(II) complexes with N4-donor Schiff bases

Abstract The reactions of hydrated RuCl3 and tetradentate Schiff bases (L=paen, papn and pabn) derived from 2-pyridine-carboxaldehyde and linear diamines such as 1,2-diaminoethane, 1,3-diaminopropane and 1,4-diaminobutane in boiling methanol afford complexes of general formula trans-[RuLCl2]. The complexes were characterised by analytical, spectroscopic and electrochemical data. All the complexes are diamagnetic and electrically non-conducting. Thus in each complex the metal ion is in +2 oxidation state. The molecular structures of trans-[Ru(papn)Cl2] and trans-[Ru(pabn)Cl2] in the solid state have been determined by X-ray crystallography. In each molecule, the ruthenium(II) centre is in distorted octahedral N4Cl2 coordination sphere. The neutral ligand coordinates via two pyridine-N and two imine-N atoms forming a N4 square-plane around the metal ion. The chloride ions satisfy the remaining two trans sites. The proton NMR spectra of all the complexes in CDCl3 solutions are consistent with the trans arrangement of the chloride ions. Electronic spectra of the complexes in dichloromethane solutions display intense metal-to-ligand charge transfer bands in the range 595–656 nm. Cyclic voltammograms of the complexes in acetonitrile solutions display a reversible oxidation response in the potential range 0.26–0.40 V (vs. saturated calomel reference electrode) due to RuIII/RuII couple.

A dimeric pervanadyl (VO2+) complex with a tridentate Schiff base ligand

AbstractA di(μ-oxo)-bridged dinuclear complex, [VO2(pamh)]2 was isolated by reacting bis(acetylacetonato)vanadium(IV) and the Schiff base, N-(anisoyl)-N′-(picolinylidene)-hydrazine (Hpamh) in acetonitrile. The complex crystallizes in the space group

Dithiolate‐Bridged Fe‐Ni‐Fe Trinuclear Complexes Consisting of Fe(CO)3−n(CN)n (n=0, 1) Components Relevant to the Active Site of [NiFe] Hydrogenase

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