Tetrakis(2-amino-4-methylbenzothiazolato)dimolybdenum tetrahydrofuranate, tris(2-amino-4-methylbenzothiazolato)(acetato)dimolybdenum bis(tetrahydrofuranate), and tetrakis(2-amino-4-chlorobenzothiazolato)dimolybdenum bis(tetrahydrofuranate). Quadruply bonded compounds with bridging ligands derived from a five-membered ring system