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

The preparation and characterization of two mononuclear cobalt­(III) tropocoronand complexes, [Co­(TC-5,5)]­(BF4) and [Co­(TC-6,6)]­(BPh4), 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)]­(GaCl4) and [Ga­(TC-6,6)]­(GaCl4) analogues. The spin state of the pseudotetrahedral [Co­(TC-6,6)]­(BPh4) 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 = BPh4, BAr′4) and [Co­(TC-4,4)]­(BPh4), respectively.