Synthesis and Characterization of Mononuclear, Pseudotetrahedral Cobalt(III) Compounds

[Image: see text] The preparation and characterization of two mononuclear cobalt(III) tropocoronand complexes, [Co(TC-5,5)](BF(4)) and [Co(TC-6,6)](BPh(4)), 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)](GaCl(4)) and [Ga(TC-6,6)](GaCl(4)) analogues. The spin state of the pseudotetrahedral [Co(TC-6,6)](BPh(4)) 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) (X = BPh(4), BAr′(4)) and [Co(TC-4,4)](BPh(4)), respectively.