Mr=465.1, orthorhombic, Pna2~, a= 20.069 (6), b= 10.633 (3), c=9.050 (2) A, V= 1931 (1) A 3, Z = 4, D x = 1.599, D m = 1.59 gcm -3, 2(Mo K~t) = 0.71069 A, p = 13.9 cm -1, F(000) = 920, T-- 295 K. Final R = 0.023 for 1362 unique observed reflections. The possible modes of bonding of the benzoate anion to In are discussed; a three-centre orbital interaction is proposed. Introduction. In a recent paper (Peppe, Tuck & Victoriano, 1982) we have described some of the synthetic applications of solutions of indium(I) halides in non-aqueous media. One reaction of particular interest corresponds formally to the oxidative insertion of InX (X= CI, Br or I) into an A-B bond to give species A InX(B). Although such reactions with alkyl halides (i.e. A-B = C-X) were reported some years ago (Waterworth & Worrall, 1971; Poland & Tuck, 1972), the availability of the solution-phase reaction has now allowed us to extend these investigations to substrates involving elements of Group V and VI. The products of the reaction between InC1 and dibenzoyl peroxide in dichloromethane/pyridine solution included the title compound CI2In(O2CC6Hs)py 2 (py = pyridine). We have established the structure of this substance by X-ray crystallographic methods. The results allow some interesting comparisons with results for pre- viously studied indium(III) complexes, and lead to a discussion of the bonding between In and the carboxy- late ligand. Experimental. Equimolar quantities of indium(I) chloride and dibenzoyl peroxide (ca 5 mmol) were mixed with 50 ml dichloromethane at 193 K. Pyridine (4 ml) was then added and the temperature allowed to rise slowly to ambient; after being stirred for 5 d, the reaction mixture was a deep-red solution over a brown solid. Addition of diethyl ether to the solution caused the precipitation of further brown solid, which was removed by filtration. The resultant solution slowly deposited a yellow solid, which was removed, and on further standing the filtrate deposited colourless acicular crystals of C12In(OzCC6Hs)py2, whose com- position was established by elemental analysis and * To whom correspondence should be addressed.