Subodh Kanti Dutta

Mono- and dinuclear oxovanadium (IV) compounds containing VO(ONS) basic core: synthesis, structure and spectroscopic properties

Abstract Reaction of [VO(acac)2] with S-methyl 3-(2-hydroxyphenyl) methylenedithiocarbazate (H2L1) and its nitro- (H2L2) and bromo derivatives (H2L3) as tridentate heterodonor (ONS)2− ligands offers a basic VO(ONS) core. In the presence of bidentate (N,N′) donor ancillar ligands, various mono- and dinuclear oxovanadium(IV) complexes [VOL(2,2′-bipy)] (1–3), [VOL(Phen)] (4, 5) and [LOV(μ-4,4′-bipy)VOL] (4, 5) and [LOV(μ-4,4′-bipy)VOL] (6–8) were obtained. The compounds have been characterized by EPR, electronic and FAB mass spectroscopic studies. The X-ray crystal structure of a representative compound [VOL2(2,2′-bipy)] (2) is reported and shows the presence of the tridentate ONS ligand occupying the meridional sites leading to distorted octahedral geometry. The nitrogen donor, occupying an apical position has a trans-labilizing influence, resulting in elongation of the VO terminal bond. Magnetic susceptibility and EPR spectral studies indicate non-interacting nature (vbJ vb ≈ 0) of the vanadium(IV) unpaired electrons in the dinuclear complexes (6–8).

Utilization of LVO2− species (L2− is a tridentate ONS donor) as an inorganic analogue of carboxylate group: A journey to a new domain of coordination chemistry

The anionic cis-dioxovanadium (V) complex species LVO2- of tridentate biprotic dithiocarbazate-based ligands H2L (S-methyl-3-((5-R-2-hydroxyphenyl)methyl)dithiocabazate, R = H, L = L1; and R = Br, L = L2) can bind alkali metal ions. The products [LVO2M(H2O)n] (M = Na+, L = L1,1; L = L2, 2 and M = K+, L = L1,3) have extended chain structures in the solid state, stabilized by strong hydrogen bonding and Coulombic interactions as revealed from X-ray crystallography. The LVO2- moieties here behave like analogues of carboxylate groups and display interesting variations in their binding patterns. It appears thatl is a single stranded helicate with LVO2- units forming the strands which surround the labile sodium ions occupying positions on the axis. The compounds are stable in water and methanol as solvents, while in aprotic solvents of higher donor strengths, viz. CH3CN, DMF and DMSO, they undergo photo-induced reduction when exposed to visible light, yielding green solutions from their initial yellow colour. The putative product is a mixed-oxidation (μ-oxo)divanadium (IV/V) species as revealed from EPR, electronic spectroscopy, dynamic1H NMR, and redox studies.

Mononuclear manganese(III) complexes of a heterodonor (N2OS) ligand containing thiolate-type sulfur: synthesis, structure, redox and spectroscopic properties

Two series of five-co-ordinate high-spin (S= 2) mononuclear manganese(III) complexes have been prepared of general formulae [MnL(X)](X = Cl 1a, Br 1b, NCS 1c or N31d) and [MnL(B)]CIO4[B = pyridine (py)2a, 3-methylpyridine (3Me-py)2b or 4-methylpyridine (4Me-py)2c] using methyl 2-[2-(salicylideneamino)ethylamino]cyclopent-1-ene-1-carbodithioate (H2L) as tetradentate ligand with a (N2OS)2– donor set. The complexes have been characterised by a combination of IR and UV/VIS spectroscopy, magnetic measurements and electrochemical studies. Their UV/VIS spectra show two ligand-field transitions at ca. 685 (5B1→5E) and 570 nm (5B1→5B2) along with a strong charge-transfer band in the near-UV region (ca. 440 nm), assigned as a phenolate O→Mn(dπ·) ligand-to-metal charge-transfer transition. Cyclic voltammograms of the complexes (except 1d) exhibit a one-electron quasi-reversible MnIII–MnII reduction with E½ close, to –0.12 V (vs. saturated calomel electrode). For 1a–1c irreversible MnIII–MnIV oxidation is also observed. The compounds have an axially elongated square-pyramidal structure as dictated by the Jahn–Teller effect with ligands X or B occupying the axial position. Their electronic spectra and electrochemical properties show invariance with group X (or B) in the axial position. The crystal structure of complex 1b was solved by Patterson and Fourier methods followed by a least-squares refinement to a conventional R value of 0.037. The basal plane of the five-co-ordinated manganese centre is defined by N (two), S and O atoms, derived from the ligand L. The co-ordinated S atom behaves like a thiolate anion as reflected by the C–S bond distance 1.717(9)A.

Chemistry of molybdenum. Part 9. Non-oxomolybdenum(IV) and mononuclear oxomolybdenum(V) complexes with dithioacid ligands

The syntheses and characterisation of a series of non-oxomolybdenum(IV) and mononuclear oxomolybdenum(V) complexes are described with 2-aminocyclopent-1 -ene-1 -carbodithioate (acda) and its N-alkyl derivatives [aacda; alkyl = ethyl (eacda), propyl (pacda) or butyl (bacda)] as the bidentate (S–S)– donor ligands. The molybdenum(IV) complexes [Mo(ox)(aacda)(acda)](ox = oxalate) are feebly paramagnetic (ca. 0.9 µB) with a spin-paired d2 ground state. They exhibit rich electrochemistry consisting of two reversible one-electron couples: MoIV–MoIII(E1/2≈–0.45 V) and MoIV–MoV(E½+0.54 V), indicating conservation of the six-co-ordinated structure in [Mo(ox)(aacda)(acda)]Z(z=–1, 0 or +1). The molybdenum(V) complexes [MoOCl(L)2](L = acda 2a, eacda 2b, pacda 2c or bacda 2d) are paramagnetic (1.56 – 1.68 µB) with one unpaired electron. Their electronic spectra in the visible region are dominated by high intensity multiple bands arising from S(π)→ Mo(dπ) charge transfers. The cyclic voltammograms of the complexes show a reversible, one-electron MoV–MoIV reduction and an irreversible MoV–MoIV oxidation. In frozen solution (80 K), 2a has an axially anisotropic ESR spectrum indicating axial co-ordination of Cl. For the remaining compounds 2b–2d the features are much more complicated due to the hyperfine interactions from the chloro ligand providing evidence for possible equatorial co-ordination of Cl.

Refinement of the crystal structure of diaqua-(3,10-C-meso-3,5,7,7, 10,12,14,14-octamethyl-1,4,8,11-tetraazacyclotetradecane)copper(II) diperchlorate, [Cu(C18H40N4)(H2O)2](ClO4)2, at 173 K

C18H44CI2C11N4O10, monoclinic, P\2\!c\ (No. 14), a = 8.111(2) A, b= 15.993(4) Κ c= 10.344(4) Α, β = 102^6(2)°, V= 1309.7 Ä, Z=2, /fgt(F)=0.045, wRretfF) = 0.042, T= 173 K.