Bijan Kumar Roy

Mixed-ligand chelates of osmium(II/III) 8-quinolinolates: Synthesis, characterization and redox behaviour

A group of mixed-tris chelates of osmium(III) and osmium(IV) of type [OsAQ2]0/1 + [HA = glycine (glyH), picolinic acid (PicH) and quinaldic acid (qndH); HQ = 8-quinolinol] were prepared and characterized by physicochemical, magnetic and spectroscopic methods. The complexes exhibit several spin-allowed and spin-forbidden absorption bands and shoulders in the 200–700 nm region. The new chelates are electroactive and display nearly reversible OsIV-OsIII and OsIII-OsII couples in the ca. −1.1 to +0.3 V range versus s.c.e. The stability of metal oxidation states is discussed in terms of the electrochemical results.

Heteroleptic tris-complexes of osmium(III/IV)8-quinolinolates: synthesis, characterization and link-up of oxidation levels

SummaryA series of mixed-tris chelates of OsIII and OsIV of the general formula [OsDQ2]0/1+ [D =β-ketoenolates (D1-D3) or tropolonate (D4); Q = deprotonated 8-quinolinol] has been prepared and characterized by physico-chemical and spectroscopic methods. In MeCN solution the OsN2O4 unit displays reversible OsIV-OsIII and OsIII-OsII couples in the ca. - 1.2 to + 0.3 V range versus s.c.e. An irreversible oxidative response corresponding to a higher degree of oxidation is also observed at ca. 1.6 V. The chemistry in different oxidation states is discussed in terms of the electrochemical results.

The COAPI Cats: The Current State of Open Access Repository Movement and Policy Documentations

The paper investigates open access (OA) self archiving policies of different Open Access Repositories (OARs) of COAPI (Coalition of Open Access Policy Institutions) founder members as reported in June 2011 (i.e. a total of 22 members against a total of 46 COPAI members as reported by Open Biomed (http://openbiomed.info/2011/08/coapi-cats/). The paper consulted three databases (OpenDOAR, ROAR and ROARMAP) in order to evaluate twenty-two (22) COAPI-members OARs self archiving policy documentations and highlights of some progress on issues so far. After analyzing policy documentations, key findings have been highlighted and common practices have been suggested in line with global recommendations and best practice guidelines at national and international levels for strengthening national research systems. The paper has implications for administrators, funding agencies, policy makers and professional librarians in devising institute specific self archiving policies for their own organization.

Synthesis, characterization and reactivity of electrophilic mono- and binuclear nitrosyls of osmium(II)ketoximates

The reaction of [OsX2(HL)(L)] (1) {X = Cl or Br; HL = PhC(O)C(=NOH)Ph (HL1) or PhC(O)C(=NOH)Me (HL2)] with n-BuONO yields mononuclear [OsX(NO)(L1)2] (2) or binuclear [OsX2(NO)(L2)]22 (3) nitrosyls depending on L. The complexes are also obtained by reacting (1) with NaNO2 plus HCl. Molecular weight determinations are in agreement with mono- and binuclear formulations. The diamagnetic orange-red nitrosyls exhibit ν(NO) at ca. 1890 cm−1 indicating NO+ character of the bound nitrogen monoxide. In 1H-n.m.r. a single sharp L2 methyl signal is in line with the centrosymmetric geometry (4) of the binuclear nitrosyls. The complexes display both spin-allowed and -forbidden charge transfer transitions in the 1000–200 nm range. Both (2) and (3) are electroactive and reductions characteristic of mono- and binuclear compositions are observable on the negative side of s.c.e. They react smoothly with acetylacetone (acacH) in the presence of K2CO3 yielding K[Os(acamo)(L1)2] (5) and K[Os(acac)(acamo)(L2)] (6) [acamo = deprotonated MeC(O)C(=NOH)C(O)Me] respectively.

Reaction of 2-(arylazo)pyridine complexes of type [OsX2L2] (X = Cl or Br) with heterocyclic bases (B): spectra and electrochemistry of [OsX(B)L2]ClO4H2O

SummaryThe synthesis and characterization of a series of complexes of the type [OsX(B)L2] + (X = Cl or Br, B = pyridine (py) and pyrazine (pyz), L = 2-(phenylazo)pyridine (L1) or 2-(m-tolylazo)pyridine (L2)) is described. The cations have been isolated as crystalline perchlorate monohydrates after purification by column chromatography. The diamagnetic compounds display several spin-allowed and spin-forbidden m.l.c.t. transitions in the visible region. The metal-centred oxidations and ligand-based reductions of the complexes are studied electrochemically in MeCN. Two consecutive one-electron oxidations corresponding to OsIII/OsII and OsIV/OsIII couples occur at ca. 1.3 and ca. 2.3 V versus s.c.e. respectively. Four successive azo-reductions are observable in the potential range -0.4 to -2.4V.

High potential isomeric dihalobis[2-(arylazo)pyridine] osmium(III) perchlorate monohydrate

SummaryThe preparation of isomeric complexes [OsIIIX2L2]ClO4· H2O [{(4)} and (5): X = Cl or Br, L(1) = 2-(phenylazo)-pyridine (L1) or 2-(m-tolylazo)pyridine(L2)] via stereo-retentive oxidation of the corresponding osmium(II) precursors [(2) and (3), respectively] is described. The complexes were characterized using spectroscopic and electrochemical methods. The low-spin (idealized t2g5; S = 1/2) paramagnetic complex ions display characteristic osmium(III) e.p.r. spectra in frozen (-196° C) MeCNPhMe. In dry MeCN solution, the OsX2N4 unit exhibits irreversible [OsX2L2]2+/[OsX2L2]+ and reversible [OsX2L2]+/[OsX2L2] couples at ca. 1.8 and 1.0 V versus saturated calomel electrode (s.c.e.), respectively. The use of (4)/(5) as an oxidant is noted.

Mixed-ligand complexes of osmium(III/II)8-quinolinolates with one diimine/azoimine ligand

SummaryParamagnetic [OsIIIDQ2]+ and diamagnetic [OsIIAQ2] (Q = deprotonated 8-quinolinols, D = diimines and A = azoimines) complexes were prepared and characterised by physicochemical, magnetic and spectroscopic methods. The complexes exhibit several spin-allowed and spinforbidden charge-transfer transitions in the visible region. In MeCN solution the OsN4O2 unit displays nearly reversible OsIV-OsIII and OsIII-OsII couples in the ca. -0.4 to +1.1 V range versus SCE. An anodic shift of these responses is seen in going from diimines to azoimines. The stability of metal oxidation levels is correlated on the basis of π-acceptor properties of these ligands.