R. Borthakur

Synthesis and spectral studies of nickel(II) complexes derived from disalicylaldehyde oxaloyldihydrazone

The mononuclear nickel(II) complex [Ni(H2slox)(H2O)3] (1) and polymeric dinuclear complexes [Ni2(slox)(A4)] {A = H2O (2), py (3), 2-pic (4), 3-pic (5) and 4-pic (6)} and the discrete binuclear complexes [Ni2(slox)(NN)3] {NN = bpy (7) and phen (8)} have been synthesized from disalicylaldehyde oxaloyldihydrazone (H4slox) in methanol. All of the complexes are nonelectrolytes. Complexes 1, 7, and 8 are paramagnetic while binuclear 2–6 possess anomalously low μ eff value, indicating considerable metal–metal interaction. Discrete binuclear 7 and 8 have no interaction between the two nickel(II) ions. The anomalously low magnetic moment values in 2–6 are explained as metal–metal interaction via phenoxide bridge. Such metal–metal interactions are less in 7 and 8 due to coordination of bipyridine and phenanthroline molecules which do not allow phenoxide bridging. The dihydrazone coordinates to the metal center as a dibasic tridentate ligand in keto-enol form in staggered configuration in 1, while in the remaining complexes the dihydrazone is tetrabasic hexadentate in enol form in anticis configuration. The metal center has a tetragonally distorted octahedral stereochemistry.

Synthesis of homobimetallic molybdenum(VI) complex of bis(2-hydroxy-1-naphthaldehyde)malonoyldihydrazone and its reaction with electron and proton bases

The diamagnetic dioxomolybdenum(VI) complex [(MoO(2))(2)(CH(2)L)(H(2)O)(2)]H(2)O (1) has been isolated in solid state from reaction of MoO(2)(acac)(2) with bis(2-hydroxy-1-naphthaldehyde)malonoyldihydrazone (CH(2)LH(4)) in 3:1 molar ratio in ethanol at higher temperature. The reaction of the complex (1) with electron donor bases gives diamagnetic molybdenum(VI) complexes having composition [Mo(2)O(5)(CH(2)LH(2))].2A.2H(2)O (where A=pyridine (py, 2), 2-picoline (2-pic, 3), 3-picoline (3-pic, 4), 4-picoline (4-pic, 5)). Further, when the complex (1) is allowed to react with protonic bases such as isonicotinoylhydrazine (inhH(3)) and salicyloylhydrazine (slhH(3)), reduction of molybdenum(VI) centre occurs leading to isolation of homobimetallic molybdenum(V) complexes [Mo(2)(CH(2)L)(inh)(2)(H(2)O)(2)] (6) and [Mo(2)(CH(2)L)(slh)(2)] (7), respectively. The composition of the complexes has been established by analytical, thermo-analytical and molecular weight data. The structure of the molybdenum(VI) complexes (1)-(5) has been established by electronic, IR, (1)H NMR and (13)C NMR spectral studies while those of the complexes (6) and (7) by magnetic moment, electronic, IR and EPR spectral studies. The dihydrazone is coordinated to the metal centres in staggered configuration in complex (1) while in anti-cis configuration in complexes (2)-(7). The complexes (6) and (7) possess magnetic moment of 2.95 and 3.06 BM, respectively, indicating presence of two magnetic centre in the complexes per molecule each with one unpaired electron on each metal centre without any metal-metal interaction. The electronic spectra of the complexes are dominated by strong charge transfer bands. All of the complexes involve six coordinated molybdenum centre with octahedral arrangement of donor atoms except in the complex (6), in which the molybdenum centre has rhombic arrangement of ligand donor atoms. The probable mechanism for generation of oxo-group in the complexes (2)-(5) involving coordinated water molecule has been proposed.

Synthesis and characterization of a binuclear copper(II) complex [Cu(H2slox)]2 from polyfunctional disalicylaldehyde oxaloyldihydrazone and its heterobinuclear copper(II) and molybdenum(VI) complexes

The binuclear copper complex [Cu(H2slox)]2 (1) and heterobinuclear copper and molybdenum complexes [Cu(slox)MoO2(A)2] (slox = tetranegative disalicylaldehyde oxaloyldihydrazone) (A = H2O (2), py (3), 2-pic (4), 3-pic (5), 4-pic (6)) and [Cu(slox)MoO2(NN)] (NN = bpy (7) and phen (8)) have been synthesized from disalicylaldehyde oxaloyldihydrazone in methanol and characterized by various physico-chemical and spectroscopic techniques. The stoichiometry of the complexes has been established based on elemental analyses and thermoanalytical studies. The µ eff values for the complexes rule out metal–metal interaction between the metal centers in the structural unit of the complexes. The dihydrazone has keto-enol forms; in 1, it is a dibasic tetradentate bridging ligand in enol form and in heterobinuclear complexes as a tetrabasic hexadentate bridging ligand. Electronic spectra of the complexes show that copper(II) is square-planar in binuclear and heterobinuclear complexes; molybdenum is a distorted octahedral stereochemistry in heterobinuclear complexes. EPR spectra suggest that in all complexes, the unpaired electron is in the d x 2− y 2 orbital of copper and that the copper in heterobinuclear complexes is tetrahedrally distorted.

Synthesis, characterization and electrochemical properties of bis(μ2-perchlorato)tricopper(II) complexes derived from succinoyldihydrazones

Three new homotrimetallic copper(II) complexes ([Cu3(Ln)(ClO4)2(H2O)m] with H4Ln = H4L1 − H4L3, m = 0, 3) have been synthesized from substituted succinoyldihydrazones (H4Ln) in methanol. The composition of the complexes has been established on the basis of data obtained from analytical and mass spectral studies and molecular weight determination in DMSO. The structure of the complexes has been discussed in the light of molar conductance, magnetic moment data and electronic, EPR, IR and FT-IR spectral studies. The molar conductance values for the complexes in the region of 1.2–1.7 Ω−1 cm2 mol−1 in DMSO indicate that the complexes are nonelectrolytes. The magnetic moment values for the complexes suggest considerable metal–metal interaction in the structural unit of the complexes. Copper centres have square planar and square pyramidal stereochemistry. The EPR parameters of complexes 1 and 3 indicate that the copper centre has a doublet ground state, while for complex 2, the ground state is a mixture of both doublet and quartet states. Electron transfer reactions of the complexes have been investigated by cyclic voltammetry.

Synthesis and characterization of heterobimetallic Ni(II)–Zn(II) complexes from bis(2-hydroxy-1 -naphthaldehyde)succinoyldihydrazone

Monometallic zinc(II) and nickel(II) complexes, [Zn(H2nsh)(H2O)] (1) and [Ni(H2nsh)(H2O)2] (2), have been synthesized in methanol by template method from bis(2-hydroxy-1-naphthaldehyde)succinoyldihydrazone (H4nsh). Reaction of monometallic complexes with alternate metal(II) acetates as a transmetallator in 1 : 3 molar ratio resulted in the formation of heterobimetallic complexes [NiZn(nsh)(A)3] and [ZnNi(nsh)(A′)2] (A = H2O (3), py (4), 2-pic (5), 3-pic (6), 4-pic (7)), (A′ = H2O (8), py (9), 2-pic (10), 3-pic (11), and 4-pic (12)). The complexes have been characterized by elemental analyzes, mass spectra, molar conductance, magnetic moments, electronic, EPR, and IR spectroscopies. All of the complexes are non-electrolytes. Monometallic zinc(II) is diamagnetic while monometallic nickel(II) complex and all heterobimetallic complexes are paramagnetic. The metal centers in heterobimetallic complexes are tethered by dihydrazone and naphthoxo bridging. Zinc(II) is square pyramidal; nickel(II) is six-coordinate distorted octahedral except [ZnNi(nsh)(A)2], in which nickel(II) has square-pyramidal geometry. The displacement of metal center in monometallic complexes by metal ion has been observed in the resulting heterobimetallic complexes.

Synthesis and characterization of heterotrinuclear bis(μ2-chlorido)dicopper (II) mono zinc(II) complexes derived from succinoyldihydrazones.

Three new zinc (II)-copper (II) heterometallic trinuclear complexes of the composition [ZnCu2(L(n))(μ2-Cl)2(H2O)6]⋅2H2O (H4L(n)=H4L(1), H4L(2), H4L(3)) have been synthesized from substituted succinoyldihydrazones (H4L(n)) in methanol medium. The composition of the complexes has been established on the basis of data obtained from analytical, mass spectral studies and molecular weight determinations in DMSO. The structure of the ligand H4L(2) has been established by X-ray crystallography. The structure of the complexes has been discussed in the light of molar conductance, magnetic moment, electronic, EPR, IR and FT-IR spectral studies. The molar conductance values for the complexes fall in the region 1.2-1.7 ohm(-1) cm(2) mol(-1) in DMSO solution indicating that all of these are non-electrolyte. The magnetic moment values suggest weak M-M interaction in the structural unit of the complexes. The dihydrazone ligand is present in enol form in all of the complexes. Copper centre has tetragonally distorted octahedral stereochemistry. The EPR parameters of the complexes indicate that the copper centre has doublet state as the ground state. The electron transfer reactions of the complexes have been investigated by cyclic voltammetry.

Solvent free selective oxidation of alcohols catalyzed by a trinuclear complex with a dicopper(II)–monozinc(II) centre using hydrogen peroxide as an oxidant

The oxidation of alcohols to carbonyl compounds was investigated by an efficient catalytic system comprising of a new heterotrinuclear complex containing a dicopper(II)–monozinc(II) centre, [ZnCu2(slsch)(NO3)2(H2O)8]·2H2O with hydrogen peroxide under solvent free conditions. Primary and secondary alcohols were oxidized to the corresponding aldehydes and ketones in good to excellent yield. The newly developed catalyst system can be reused in four consecutive runs without any significant loss of activity.

An efficient oxidation of alcohols using a new trinuclear copper complex as a reusable catalyst under solvent free conditions

A new trinuclear copper(II) complex [Cu3(L)(μ2-Cl)2(H2O)6] was synthesized and characterized by various spectroscopic techniques. The trinuclear complex was demonstrated as an efficient catalyst for the selective oxidation of primary, secondary, aliphatic, heteroatomic and conjugated allyl alcohols to the corresponding aldehydes/ketones in good to excellent yields under solvent free conditions using H2O2 as an oxidant. The catalyst is easily synthesizable, easy to handle and reusable up to eight runs.

Synthesis and characterization of molybdenum(V,VI) complexes derived from bis(2-hydroxy-1-naphthaldehyde)malonoyldihydrazone

Monometallic molybdenum(VI) complexes [MoO2(CH2LH2)] · H2O (1), [Mo2O4(CH2LH2)2(A)2] (A = py (2), 2-pic (3), 3-pic (4) and 4-pic (5)) and molybdenum(V) complexes [Mo(CH2LH2)(inh)] · H2O (6) and [Mo(CH2LH2)(slh)] (7) of bis(2-hydroxy-1-naphthaldehyde)malonoyldihydrazone (CH2LH4) have been synthesized and characterized by various physico-chemical and spectroscopic studies. The compositions of the complexes have been established by elemental analyses and molecular weight determination. The structural assessment of the complexes has been done on the basis of data obtained from molar conductances, magnetic moment studies, electronic, infrared, electron paramagnetic resonance (EPR), proton nuclear magnetic resonance, and 13C proton nuclear magnetic resonance spectroscopic studies. The molar conductance values for the complexes in DMSO suggest that they are non-electrolytes. The magnetic moment values for 6 and 7 correspond to one unpaired electron while the remaining complexes are diamagnetic. Complexes 1, 6, and 7 have six-coordinate octahedral stereochemistry around molybdenum, while 2–5 are eight-coordinate dodecahedral around the metal centers. EPR spectral features suggest that 7 is less symmetrical than 6.

Synthesis, characterization and electrochemical studies of some NiIICuII heterobimetallic complexes derived from succinoyldihydrazones ☆

Synthesis, structural characterization and redox properties of three heterobimetallic complexes with formule {[NiCu(L(n))(CH3OH)3]·CH3OH} using [Cu(H2L(n))(H2O)] as metalloligand have been demonstrated in the present paper. Electronic spectroscopy suggests that the copper center has a pseudo square pyramidal stereochemistry in all the complexes while the nickel center has a distorted octahedral stereochemistry. The electron transfer reactions of the complexes have been investigated by cyclic voltammetry.