Chandan Kumar Pal

SYNTHESIS, STRUCTURE AND PROPERTIES OF A DICOPPER(II) COMPLEX

Abstract A dinuclear copper(II) complex, [Cu2(bhsNO2)2(H2O)2] was isolated by reacting Cu(O2CCH3)2·H2O and 2-hydroxy-5-nitrobenzaldehyde benzoylhydrazone (H2bhsNO2) in methanol. The X-ray structure of the complex has been determined. The dinegative ligands bind the Cu(II) ions through the deprotonated amide–O, imine–N and phenolate–O atoms. The pair of Cu(II) ions are linked by the two phenolate–O atoms. The coordination geometry around each Cu(II) is square pyramidal. The imine–N, amide–O and the bridging phenolate–O atoms form the square plane and the oxygen atom of a water molecule occupies the axial coordination site. The complex is redox active. Variable temperature (25–300 K) magnetic susceptibility measurements in the solid state are consistent with an antiferromagnetic interaction between the two metal centres. The coupling constant J is found to be −186(5) cm−1 by least-squares fitting of the magnetic susceptibility data using an expression derived from the isotropic spin Hamiltonian, H=−2JS1·S2 (S1=S2=1/2).

Facile regiospecific aromatic hydroxylation in palladium azopyridines and structural characterization of phenolato product

Abstract The reaction of Na2PdCl4 with 2-(arylazo)pyridines (A) in ethanol affords yellow complexes of composition [PdACl2] in which the PdCl2 fragment has acis configuration [ν(Pd Cl): 350, 365 cm−1]. Upon treating [PdACl2] with dilute sodium hydroxide in air the pendent aryl group is selectively hydroxylated at theortho position, affording the phenolato complex [PdBCl] in high yields [B− is deprotonated 2-(2′-hydroxyarylazo)pyridine]. A possible reaction pathway is proposed by analogy with the hydroxylation of certain organic compounds by OH−/O2. The crystal and molecular structure of one [PdBCl] complex is reported. In the highly planar complex, the Pd N(azo) length is significantly shorter than the Pd N(pyridine) length. A single Pd Cl stretch at 365 cm−1 characterizes [PdBCl] which, unliked [PdACl2], has a structured intense absorption in the visible region near 670 nm.

Synthesis and structure of a thioazobenzene palladacycle: Oxygen insertion into the PdC bond by m-chloroperbenzoic acid

Abstract The reaction of p -tolyl- o ′-(2-chloroethylthio)azobenzene (L 1 H) with Na 2 PdCI 4 affords the complex PDL 1 CI, the structure of whi

A FeIIIO4N2 co-ordination sphere assembled via an enolate–imine–amide ligand. Effect of amide protonation on the redox behaviour and stereochemistry of the iron(III) centre

The reaction of anhydrous FeCl3, acetylacetone benzoylhydrazone (H2L) and KOH (1 : 2 : 3 mole ratio) in methanol produced an iron(III) complex, [FeL(HL)]1, the crystal structure of which was determined. Each ligand binds through enolate O, imine N and amide O atoms in meridional fashion. In the dianionic L both the enolic OH and the amide protons are dissociated, whereas in the monoanionic HL only the enolic OH is deprotonated. Addition of 1 equivalent of HClO4 to 1 in MeOH gave [Fe(HL)2]ClO42. Similarly reaction of 1 equivalent of KOH with 1 yielded K[FeL2]3. All the complexes were characterized by analytical, spectroscopic, electrochemical and magnetic measurements. The metal centre in 1 is redox inactive. However, in cyclic voltammetric experiments 2 displayed FeIII→ FeII reduction at –0.21 V and for 3 an oxidation at 0.40 V (vs. saturated calomel electrode) was observed due to FeIII→ FeIV oxidation. Magnetic moments (at 298 K) of the three complexes reflect a S= 5/2 spin state in each. The ESR spectra (at 298 K) of polycrystalline 1 and 2 are rhombic. On the other hand, an ideal axial spectrum was observed for 3.

Generation of manganese-(III) versus-(IV) complexes with a conjugated ONS donor set: controllingeffect of ligand substituents†

Manganese(IV) complexes, [MnL 2 ] [H 2 L = MeC(OH)CHCMeNN C(SH)SR (R = Me 1a or CH 2 Ph 1b)] and manganese(III) complexes, [Mn(O 2 CMe)L] 1c or [Mn(acac)L] 1d [acac = acetylacetonate; H 2 L = PhCH(OH)CPhNNC(SH)SCH 2 Ph] have been synthesized and characterized. The Schiff-base ligands which are derived from an aliphatic carbonyl function, favour the facile oxidation of manganese-(II) to -(IV) under ambient conditions. The structure determination of 1a showed that the molecule is octahedral with the two equivalent tridentate ligands spanned meridionally. The EPR spectrum of 1a with a strong but structured signal at g ≈ 4.0 and a weak one at g ≈ 2.0 implies a large zero-field splitting, but the spectral profile differed from an ideal axial form. All the complexes exhibited reversible or quasi-reversible Mn IV –Mn III redox couples in their cyclic voltammograms at potentials commensurate with the nature of the substituents in the appropriate ligands. A reasonable basis is suggested by which one may predict whether a particular ligand will stabilize manganese-(II), -(III) or -(IV) in an aerobic medium.

Synthesis, spectroscopic characterisation, electron-transfer propertiesand crystal structure of[RuII(bipy)2(2-SC5H4N)]ClO4 (bipy = 2,2′-bipyridine)

Two new ruthenium(II) mixed-ligand tris-chelated complexes of the type [Ru(bipy) 2 L]ClO 4 , (bipy = 2,2′-bipyridine; L = pyridine-2-thiolate 1 or pyridin-2-olate 2) have been synthesized. The complexes are essentially diamagnetic and behave as 1∶1 electrolytes in acetonitrile solution. They display two metal-to-ligand charge-transfer (m.l.c.t.) transitions near 500 and 340 nm respectively along with intraligand transitions in the UV region. Both exhibit room-temperature emission from the highest-energy (m.l.c.t.) band. At room temperature the lifetime of the excited states for the thiolato (1) and phenolato (2) complexes are 100 and 90 ns respectively. The geometry of the complexes in solution has been assessed by high-resolution 1 H NMR spectroscopy. The molecular structure of complex 1 in the solid state has been determined by single-crystal X-ray diffraction. It shows the expected pseudo-octahedral geometry with considerable strain due to the presence of the sterically hindered ligand L 1 . In acetonitrile solution the complexes show quasi-reversible ruthenium(II)–ruthenium(III) oxidation couples at 0.54 and 0.64 V versus saturated calomel electrode and quasi-reversible ruthenium(III)–ruthenium(IV) oxidations at 1.41 and 1.03 V respectively. Two reversible reductions are observed near -1.6 and -1.9 V for each complex due to electron transfer to the co-ordinated bipy units. The trivalent analogues of 1 and 2 are unstable at room temperature but can be generated in solution by coulometric oxidation at 263 K as evidenced by EPR spectroscopy.