Some trimethyl-substituted antimony(V) compounds containing Sb-O bonds such as trimethylantimony dicarboxylates, dinitrate or oxybis(trimethylantimony) dinitrate, were prepared. From the infrared spectroscopic investigation, both in the solid and in solution, and cryoscopic molecular weight determinations in benzene, the following results were obtained. (1) (CH 3) 3SbX 2 (where X is OCOR or NO 3) has a trigonal bipyramidal configuration with the C 3Sb group in the same plane and X at the apices. (2) The Sb-O bond in (CH 3) 3SbX 2 (where X is OCOR or NO 3) is covalent in nature while the Sb-O bond in oxybis(trimethylantimony) dinitrate is intermediate in character between covalent and ionic bonds.