Synthesis and characterization of mononuclear, pseudotetrahedral cobalt(III) compounds.

The preparation and characterization of two mononuclear cobalt(III) tropocoronand complexes, Co(TC-5,5) and Co(TC-6,6), are reported. The cobalt(III) centers exist in rare pseudotetrahedral conformations, with twist angles of 65° and 74° for the Co(TC-5,5 and Co(TC-6,6) species, respectively. Structural and electrochemical characteristics are compared with those of newly synthesized Ga(TC-5,5) and Ga(TC-6,6) analogues. The spin state of the pseudotetrahedral Co(TC-6,6) compound was determined to be S = 2, a change in spin state from the value of S = 1 that occurs in the square-planar and distorted square-planar complexes, Co(TC-3,3) (X = BPh4, BAr'4) and Co(TC-4,4), respectively.