Synthesis and characterization of tetraalkylammonium salts of bis(5,6-dihydro-1,4-dithiin-2,3-dithiolato)cobaltate(III). Crystal structure of [(C 4H 9) 4N] 2[Co(DDDT) 2] 2

Abstract

The reaction between CoCl 2·6H 2O and K 2DDDT (the potassium salt of 1,2-dithiolene 5,6-dihydro-1,4- dithiin-2,3-dithiolate) under an argon atmosphere yields a dimeric dianion which can be isolated as a tetraalkylammonium salt. Constant potential electrolysis of the formally Co(III) product yields a Co(II) species. Both complexes are extremely sensitive to air in solution. The solid Co(III) product, however, is sufficiently air stable to allow a structural analysis of the tetrabutylammonium salt. The crystal belongs to the monoclinic space group C2/ c with unit cell dimensions of a=23.626(3), b=16.915(3), c= 16.294(2) Å, β=101.62(1) °, Z=8. The coordination around the cobalt atom is best described as square pyramid with an average basal CoS bond length of 2.197(1) Å and an apical CoS distance of 2.328(1) Å. The dimeric structure allows for S…S contacts in the crystal lattice as short as 3.22 Å. The structure refined to R=0.037 and R w=0.053. The frozen glass ESR spectrum of the Co(II) complex exhibits three sets of eight lines with g 1=1.933, g 2=2.067 and g 3=2.860. A cyclic voltammogram contains a two-electron reversible wave, a quasi-reversible one- electron wave and a reversible one-electron wave indicating a four-member electrochemical series: [Co- (DDDT) 2] 2 o[Co(DDDT) 2] 2 − ⇄[Co(DDDT) 2] 2 2−⇄2Co(DDDT) 2 2−. The solid-state 13C NMR spectrum shows different resonances for carbons in the double bonds of the ligand, consistent with splitting of the C=C stretch in the IR spectrum.