Syntheses, electrochemistry, and spectroscopic and magnetic properties of new mononuclear and binuclear complexes of vanadium(III), -(IV, and -(V) containing the tridentate macrocycle 1,4,7-trimethyl-1,4,7-triazacyclononane (L). Crystal structures of [L2V2(acac)2(.mu.-O)]I2.2H2O, [L2V2O4(.mu.-O)].14H2O, and [L2V2O2(OH)2(.mu.-O)](ClO4)2