Oxidative fragmentation of the cuboid molybdenum-sulfur Mo4S4 cluster core: synthesis and structures of [Mo3(.mu.3-S)(.mu.-S)3([9]aneN3)3]4+ and {[MoO([9]aneN3)]2(.mu.-S)2}2+ ([9]aneN3 = 1,4,7-triazacyclononane)