Molecular adduct of dimethyltin dichloride with methyl N-(2-hydroxybenzylidene)alaninate (1:2), [SnCl2(C11H13NO3)2(CH3)2]

Abstract

The structure of the 2:1 complex of methyl N-(2-hydroxybenzylidene)alaninate with dimethyltin dichloride, dichlorobis(2-{[1-(methoxycarbonyl)-ethyl]iminiomethyl}phenolato-O)dimethyltin, has been determined. The coordination of the Sn atom is octahedral, all trans, with bond distances Sn--CI = 2.599 (1), Sn--O = 2.244 (3) and Sn--C = 2.111 (4)A.The ligands are coordinated to SnActa Crystallographica Section C ISSN 0108-2701 ©i994A. HAZELL, N. K. GOH AND L. E. KHOO 55 through the phenolic O atoms, the hydroxylic H atoms being shifted to the imine N atoms giving rise to a zwitterion. There is intramolecular hydrogen bonding with N--H...O = 2.628 (4) ,~,. CommentN-Salicylidene-a-amino acid ester has been reported to form a trigonal bipyramidal adduct with triphenyltin(IV) chloride by Lee, Gabe, Khoo, Eng & Smith (1990). In addition, a shift of the phenolic proton to the imine N atom resulting in a zwitterionic configuration for the ligand has been observed. This is further substantiated by Bullock, Ladd, Povey & Tajmir-Riahi (1979) from the crystal structure and spectroscopic study of Schiff base complexes with calcium nitrate. In view of this unusual occurrence of the zwitterionic form of Schiff bases and its influence on the mode of coordination of the potentially bidentate neutral ligand, N-salicylidenea-amino acid ester, to diorganotin dichloride, a complete X-ray structural investigation of the title adduct has been undertaken. Preparation was according to Lee et al. (1990). Dimethyltin dichloride was used instead of triphenyltin chloride in a 1:2 chloroform-petroleum ether (60-80) mixture. Recrystallization from a similar mixture at room temperature gave soft crystals of melting point 388-390 K. Elemental analysis (NUS, Singapore) is as follows: calculated (found) for C24H32N206SnC12: C 45.45 (45.26), H 5.10 (5.13)%.The Sn atom, which is on a symmetry centre, is bonded to two C1 atoms, two methyl groups and the phenolic O atoms of the two ligands, giving an all-trans octahedral geometry. The coordination Fig. 1. A drawing of the title adduct with the atom-numbering scheme.bond angles involving the equivalent trans ligands are 180' by symmetry, the other angles range from 86.1 (1) to 93.9 (ly. The Sn--C and Sn--CI distances are normal and lie within the range for similar compounds (Lee et al., 1990;Kamwaya & Khoo, 1985). The organic ligand is monodentate bonding only, via the phenolic oxygen. Atom O14 is 4.535 (3)A from Sn and the very short C13--O14 distance of 1.187 (5)A is typical for a non-bridging carbonyl group. A similar distance of 1.179 A was reported for the corresponding carbonyl group in Ph3SnC1-2HOC6H4CHzNCH2CO2Et (Lee et al., 1990). 119.6 (4) O2. Cell dimensions were determined from reflections measured at four positions, 4-20 and high and low X. Data were corrected for background, Lorentz and polarization effects, and for absorption. The structure was determined using SHELXS86 (Sheldrick, 1986) and H atoms were located from a difference electron density map. Non-H atoms were refined a...