Osmium dithiophosphates. Synthesis, X-ray crystal structure, spectroscopic and electrochemical properties

Jain, Prateek U. ; Paul, Himadri ; Munshi, Pradip ; Walawalkar, Mrinalini G. ; Lahiri, Goutam Kumar (2001) Osmium dithiophosphates. Synthesis, X-ray crystal structure, spectroscopic and electrochemical properties Polyhedron, 20 (3-4). pp. 245-252. ISSN 0277-5387

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Official URL: http://linkinghub.elsevier.com/retrieve/pii/S02775...

Related URL: http://dx.doi.org/10.1016/S0277-5387(00)00638-0

Abstract

The reactions of ammonium salt of dialkyldithiophosphate ligands, (RO)2PS2 -NH4+ (R=Me/Et) with (NH4)2OsIVBr6 in methanol solvent and under dinitrogen atmosphere result in one-electron paramagnetic tris complexes, {(RO)2PS2}3OsIII (1a-1b) in the solid state. The molecular structure of one complex (1a) has been determined by single-crystal X-ray diffraction. It shows the expected pseudo-octahedral geometry with reasonable strain due to the presence of four-membered chelate rings. The reflectance spectra of the solid complexes display two broad bands in the range 552-484 nm and in the solid-state complexes exhibit one isotropic EPR signal at 77K. Although the complexes 1a-1b are found to be stable in the solid state, in solution state the complexes are transformed selectively into the diamagnetic and electrically non-conducting metal-metal bonded dimeric species [{(RO)2PS2}3OsIII-OsIII{S2P(OR)2}3]. The formation of dimeric species in the solution state is authenticated by the electrospray mass spectrum of one representative complex where R=Et (1b). In dichloromethane solution the complexes show two moderately strong sulfur to osmium charge-transfer transitions in the visible region and two strong ligand based transitions in the UV region. The complexes exhibit successive two oxidations correspond to OsIV-OsIV/OsIII-OsIII and OsV-OsV/OsIV-OsIV processes near 0.8 and 1.9 V versus SCE, respectively. One reductive couple corresponds to the OsIII-OsIII/OsII-OsII couple has been observed near -0.6 V. Electrochemically generated oxidized species [{(RO)2PS2}3OsIV-OsIV{S2P(OR)2}3]2+ display lowest energy ligand to metal charge-transfer transition near 550 nm which has observed to be reasonably red shifted as compared to that of the parent trivalent species. On the other hand electrochemically generated reduced species [{(RO)2PS2}3OsII-OsII{S2P(OR)2}3]2- are found to be unstable even on coulometric time scale.

Item Type:Article
Source:Copyright of this article belongs to Elsevier Science.
Keywords:Osmium Dithiophosphates; X-ray Crystal Structures; Spectroscopic Properties
ID Code:19029
Deposited On:25 Nov 2010 14:34
Last Modified:17 May 2016 03:39

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