TETRAHEDRAL COORDINATION BY A 7-MEMBERED CHELATE RING

The ligand 1,2-bis(benzimidazol-2-yl) ethane (la) and its N,N'-dioctyl (Ib), N,N'-bis(3,5-dimethoxybenzyl) (Ic) and 5,5'-dimethyl-N,N'-dieth yl (Id) derivatives have been prepared. With MCl2 the ligands give com plexes [MLCl2] (M = Mn, Fe, Co, Ni, Cu, Zn) which generally appear to have tetrahedral coordination geometry. X-ray crystal structures of [C u(lc)Cl-2]. MeCN, [Cu(lc)Br-2] and [Mn(ld)Cl-2]. MeCN have been determ ined, and show tetrahedral coordination of the metal, the copper(ll) c omplexes showing significant distortion from ideal tetrahedral charact er. Comparison with other results in the literature, coupled with simp le molecular mechanics calculations, suggests that the tetrahedral cha racter may be favoured by the seven-membered chelate ring in which puc kering is limited by the presence of two double bonds in the ring. (C) 1998 Elsevier Science S.A. All rights reserved.