Animesh Chakravorty

Charge Transfer Spectra of some Gold(III) Complexes

Tetrahalo complexes of Au(III) show two intense bands in the ultraviolet. These are interpreted as charge‐transfer bands; the transfer is from halogen p to gold d orbitals. The two bands are associated with pσ→dx2—y2 and pπ→dx2—y2 transitions. The iodo complex undergoes spontaneous reduction; reason for this is discussed. The ethylenediamine complexes of Au(III) also exhibit interesting charge‐transfer phenomenon.

Paramagnetic organometallics formed by o-metallation of phenolic Schiff bases by ruthenium(III)

Abstract The reaction of Ru(PPh 3 ) 3 X 2 (X Cl, Br) with the Schiff base condensate of 4-substituted benzaldehyde (RC 6 H 4 CHO) and 2-aminophenol under aerobic conditions affords the complexes Ru III (RL)(PPH 3 ) 2 X in which RL is the Schiff base ligand bound to the metal centre at the phenolic oxygen (deprotonated azomethine nitrogen and an ortho carbon atom (deprotonated) of the benzaldehyde fragment. The complexes behave as one-electron paramagnets; and give rhombic EPR spectra, that have been analysed to furnish values of axial and rhombic distortion parameters as well as the energies of the two expected ligand field transitions within the t 2 shell. One of the transitions has been experimentally observed in the predicted region. The complexes are electroactive and display ruthenium(III)- ruthenium(II) ( E 1/2 - 0.5 to - 0.8 V vs . SCE) and ruthenium(IV)-ruthenium(III) ( E 1/2 0.4 to 0.8 V) couples. The E 1/2 values vary linearly with the Hammett constant of the substituent R. The role of phenolato-coordination in stabilizing the trivalent state of ruthenium is noted.

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.

Chemistry of tetravalent nickel and related species. 3. Characterization and cyclic voltammetry of new [NiN6] species based on tridentate ligands

High-spin octahedral (NiN 6 core;Dg≈ 1250cm -1 ) nickel(II) complexes of type Ni(HRRI) 2 X 2 (where HRRT is a tridentate ligand of class N.β-aminoethylisonitroso ketimine and X = CI0 4 . NO 3 ) are readily oxidized by concentrated nitric acid to yield the diamagnetic nicket(IV) species Ni(RRT).K.. Cyclic voltammcry (CV) of Ni(RRT) 2 (CIO 4 ) 2 has been thoroughly done in well-buffered aqueous media over a wide range of pH. Below pH 6.0. CV data show a single reversible two-electron, two-proton transfer process followed by an irreversible chemical decomposition of the nickel(II) species. The rate constant for this decomposition reaction has been determined to be 0.16s -1 (283 K) from CV data. In the pH range 7.0-9.0. two distinct reversible onc-elcctron processes are observed corresponding to Ni(IV)-Ni(III) and Ni(III- Ni(II) couples. The first of these has no proton involvement while the other involves one proton. The E°′ 298 values for the various couples have been accurately determined front CV data. Representative results are as follows: Ni(Me 2 T) 2 2+ -Ni(HMe 2 T) 2 2+ ,0.71 V; Ni(Me 2 T) 2 2+ -Ni(Me 2 T)2 + ,0.40 V; Ni(Me 2 T)2 + -Ni(HMe 2 T)(Me 2 T) + ,0.66 V; Ni(Me 2 T)2 + -Ni(Me 2 T)2,0.07 V (estimated). The nickel(II) species involved in each of the above couples is what is expected from acid dissociation (oxime protons) data of Ni(Hme 2 T) 2 2+ (pK 1 =7.80;pK 2 =10.00).

Manganese(IV) in discrete O3S3 coordination

Preparation des complexes de Mn(IV) avec les coordinats thiohydroxamiques. Proprietes physiques, comportement redox et stereochimie

Chemistry of hydrazonato oxovanadium(V) alkoxides derived from dihydric/monohydric alcohols

Abstract The reaction of bis(acetylacetonato)oxovanadium(IV) with benzoylhydrazones of benzoylacetone and salicylaldehyde — H2babh and H2sabh, respectively — with ethane-1,2-diol (H2ed) in acetone solution has afforded the alkoxides VVO(babh)(Hed) and VVO(sabh)(Hed) in which the Hed− ligand is chelated both in the solid state and in solution. In methanol solution (no H2ed added) five-coordinated VvO(babh)(OMe) and six-coordinated VVO(sabh)(OMe)(OHMe) are formed. Aerial oxygen is the oxidant (VIV → VV) in the synthesis. The X-ray structures of VO(babh)(Hed) and VO(sabh)(OMe)(OHMe) are reported. In the VO5N coordination sphere the alcohol oxygen lies trans to the oxo oxygen. The general VO bond length order is oxo E 1 2 , −0.3 to −0.2 V ) corresponding to stabilization of the pentavalent state. The methylene protons of Hed− in the complexes are inequivalent in solution (1H NMR). Crystal data: VO(babh)(Hed): monoclinic, space group P2 1 /c, a = 11.260(6), b = 7.672(3), c = 21.072(8) A , β = 91.95(4)°, V = 1820(1.4) A 3 , Z = 4, R w = 4.67% ; VO(sabh)(OMe)(OHMe): monoclinic, space group P2 1 /c, a = 8.170(4), b = 16.984(10), c = 12.242(7) A , β = 104.24(4)°, V = 1646(1.6) A 3 , Z = 4, R = 3.64% , Rw = 4.71%.

Chemistry of platinum(IV), platinum(II) and palladium(II) cyclometallates of benzylthio- or benzosulphinyl-substituted azobenzenes

Abstract Cyclometallated platinum(IV) complexes of the type [Pt(RL)Cl3] incorporating azobenzene (R = H) or 4-methylazobenzene (R = Me) with an SCH2Ph (L = L1) or an S(O)CH2Ph (L = L2) substituent in an ortho position are described. These were obtained by oxidative addition of chlorine to [PtII(RL)Ci]. Analogous palladium(II) complexes, however, gave chloro-substituted azobenzenes upon reaction with chlorine. The platinum(IV) complexes show an irreversible cyclic voltammetric metal reduction peak near −0.3 V vs SCE. Constant potential coulometric reduction at −0.5 V or chemical reduction by hydrazine hydrate regenerated [PtII(RL)Cl]. The structures of [Pt(HL1)Cl3], Pt(MeL2)Cl] and [Pd(MeL(su1)Cl] have been determined by an X-ray diffraction study. The S(O)CH2Ph group is coordinated via the sulphur atom.

Hydroxamates of bis(2,2'-bipyridine)ruthenium: synthesis, protic, redox, and electroprotic equilibria, spectra, and spectroelectrochemical correlations

Synthese des complexes de type Ru II (bpy) 2 (RX)ClO 4 •2H 2 O avec RX=RN(O)C(O)C 6 H 4 -p-X − ; R=H, Me; X=OMe, Me, H, Cl, NO 2 . Les complexes HX agissent comme acides faibles en milieu aqueux. Isolement des complexes Ru III (bpy) 2 (MeMe) (ClO 4 ) 2 •2H 2 O et Ru III (bpy) 2 (H)ClO 4 •2H 2 O

Synthesis, structure and metal redox of new VO3+ and VO2+ complexes incorporating mixed tridentate–bidentate binding

The reaction of bis(acetylacetonato)oxovanadium(IV) with a mixture of a tridentate ONO-co-ordinating hydrazone H2L1–H2L4(general abbreviation H2L; condensates of benzoylhydrazine with benzoylacetone, salicylaldehyde, 2-hydroxy-1-naphthaldehyde and 2-hydroxybutyrophenone respectively) and a bidentate compound 2,2′-bipyridine (bipy), 1,10-phenanthroline (phen) or quinolin-8-ol (Hquin) has afforded the complexes [VIVO(L)(bipy)]. [VIVO(L)(phen)] and [VVO(L)(quin)] in high yields. The crystal structure of [VO(L1)(quin)] has been determined, revealing the distorted-octahedral VO(ONO)(ON) co-ordination sphere with the L1 ligand spanning meridionally. The VO distance is 1.592(3)A and the atom lying trans to VO is the quin nitrogen. There is a large decrease (≈ 700 mV) in the VO3+–VO2+E½ values between [VO(L)(bipy)]{or [VO(L)(phen)]} and [VO(L)(quin)]. The complex [VIVO(L)(quin)]– was electrogenerated in solution but spontaneously reoxidized to [VVO(L)(quin)] in air. For a given bidentate ligand, the VO3+–VO2+E½ values follow the order L1 < L4 < L2 < L3. The ESR spectra of the VO2+ complexes correspond to an axially compressed dxy1 configuration. The 51V hyperfine constants are slightly larger for [VO(L)(quin)]– than for [VO(L)-(bipy)] and [VO(L)(phen)]. The dxy→ dxz,dyz transition of the tetravalent complexes occurs in the region 700–950 nm.

New trinuclear copper(II) species

Bidentate isonitrosoketimine ligands containing the functions −C(NOH)C(NR)− (abbreviated as HinkR) and −C(NOH)C(NAr)− (HinkAr) readily yield trinuclear copper(II) species [Cu3O- (inkR)3]ClO4 and [Cu3OH(inkAr)3](ClO4)2 which have been characterized using solution electrical conductivity, electronic and infrared spectra and variable temperature magnetic susceptibility. The complexes uniformly have magnetic moments of ∼1.8 BM per molecule (∼ BM per copper) over the temperature range 80–380 K. The species are thus strongly antiferromagnetic in nature and only doublet states are populated. The lower limit of the exchange integral ∣J∣ is set at ∼350 cm−1. Structures containing a central Cu3O or Cu3OH core held by peripheral oximato bridge is strongly indicated by the experimental data taken collectively with some known structural information. The superexchange mechanism has been investigated. Results of EHT calculation on the Cu3O4+ core is presented. It is shown that the O bridge can bring about considerable antiferromagnetic interaction. However on the basis of experimental and theoretical results concerning the role of oximato bridge in bringing about exchange, it is suggested that the peripheral oxime bridge plays a dominant role. A new system which is most probably trinuclear and contains the Cu3 core held only by oximato group (no central oxygen) also has S = 12, thus showing the pivotal importance of the oximato bridges in relation to the strong magnetic coupling.