Reactions of di-n-butyltin(IV
) oxide with 4 /2 -nitrobiphenyl-2-carboxylic acids in 1 : 1 and 1 : 2 stoichiometry yield complexes [{(n-C 4 H 9 ) 2 Sn(OCOC 12 H 8 NO 2 -4 /2 )} 2 O] 2 (1 and 2) and (n-C 4 H 9 ) 2 Sn(OCOC 12 H 8 NO 2 -4 /2 ) 2 (3 and 4) respectively. These compounds were characterized by elemental analysis, IR and NMR ( 1 H, 13 C and 119 Sn) spectroscopy. The IR spectra of these compounds indicate the presence of anisobidentate carboxylate groups and non-linear C-Sn-C bonds. From the chemical shifts δ ( 119 Sn) and the coupling constants 1 J( 13 C, 119 Sn), the coordination number of the tin atom and the geometry of its coordination sphere have been suggested. [{(n-C 4 H 9 ) 2 Sn(OCOC 12 H 8 NO 2 -4 )} 2 O] 2 (1) exhibits a dimeric structure containing distannoxane units with two types of tin atom with essentially identical geometry. To a first approximation, the tin atoms appear to be pentacoordinated with distorted trigonal bipyramidal geometry. However, each type of tin atom is further subjected to a sixth weaker interaction and may be described as having a capped trigonal bipyramidal structure. The diffraction study of the complex (n-C 4 H 9 ) 2 Sn(OCOC 12 H 8 NO 2 -4 ) 2 (3) shows a six-coordinate tin in a distorted octahedral frame containing bidentate asymmetric chelating carboxylate groups, with the n-Bu groups trans to each other. The n-Bu-Sn-n-Bu angle is 152.8 • and the Sn-O distances are 2.108(4) and 2.493(5) Å. The oxygen atom of the nitro group of the ligand does not participate in bonding to the tin atom in 1 and 3. Crystals of 1 are triclinic with space group P1 and of that of 3 have orthorhombic space group Pnna.