Single-crystal polarized electronic spectra of the compounds tetra-[Greek letter mu]-acetatodimolybdenum(II), tetrakis-[Greek letter mu]-(trifluoroacetato)-dimolybdenum(II), potassium-diaquo-tetra-[Greek letter mu]-sulfatodiplatinum(III), and the X-ray diffraction crystal structure of tetra-[Greek letter mu]-acetatodimolybdenum(II)·potassium chloride