The nature of close Pd - Pd and Pd - H(-C) contacts - The crystal structures of R-aminohexahydroazepine-dichloropalladium(II) and N-ethyl-R-aminohexahydroazepine-dichloropalladium(II) and a molecular mechanics analysis of the close contacts

The preparations and crystal structures of [PdCl2(R-ahaz)] (ahaz=3-aminohex ahydroazepine) and [PdCl2(R-etahaz)] (etahaz=N-ethyl-3-aminohexahydroazepin e) are described. Both complexes crystallise with two independent molecules stacked in "dimeric" pairs with short Pd Pd contacts. In [PdCl2(R-ahaz)] t he Pd ... Pd separation is 3.361(1) Angstrom and in [PdCl2(R-etahaz)] it is 3.415(1) Angstrom. Hydrogen bonds between the N-H groups of one complex an d the chloro ligands of the other link the dimers. There are also Pd ... H contacts in the range 2.60 Angstrom to 2.75 Angstrom between the ligand bac kbone and the metal. Molecular mechanics models indicate that the hydrogen bonds are the major contributor to dimer formation. (C) 1999 Elsevier Scien ce Ltd. All rights reserved.