Coordination studies of the ligand series RNH•CO•(CH2)n•CO•NHR where R = alkyl, aryl; O = O, S and n = 0,1,2.: Part 6.: Crystal structures and bonding considerations of the ligands MeNH•CO•CH2•CO•NHMe (L1), MeNH•CO•CH2•CH2•CO•NHMe (L4), MeNH•CS•CH2•CS•NHMe (L5) and the SnIV complexes SnBr4L1•L1, SnBr4L2•2THF and SnBr4L3•MeCN where L2 = iC3H7NH•CO•CH2•CO•NHiC3H7 and L3 = iC3H7NH•CS•CH2•CS•NHiC3H7

Crystal structures of the ligands MeNH . CO . CH2. CO . NHMe, MeNH . CO . CH2. CH2. CO . NHMe and MeNH . CS . CH2. CS . NHMe have been determined by X-ray diffraction studies. The framework C-C, C-N, and C=O/C=S bond distances and the associated interbond angles are all closely similar and the packing of these molecules is dominated by intermolecular hydrogen bonding of the type N-H ... O=C and, to a lesser extent, N-H ... S=C. For means of comparison the bond parameters of all the structurally characterised related ligands belonging to the N,N'-disubstituted series RNH . CO (CH2)(n). CO . NHR where R = alkyl; O = O, S and n = O, 1, 2 are listed and a general overview of the characteristics of such ligands including conformational variations is provided. Structural characterisation (X-ray diffraction) of SnBr4 (MeNH . CO . CH2. CO . NHMe). MeNH . CO . CH2. CO . NHMe, SnBr4((PrNH)-Pr-i . CO . CH2. CO . (NHPr)-Pr-i). 2THF and SnBr4(iPrNH . CS . CH2CS . (NHPr)-Pr-i). MeCN reveals bidentate chelate ligand attachment for these six coordinate mononuclear cis-octahedral Sn(IV) complexes. In all three structures, the NH groups are involved in intermolecular hydrogen bonding being linked either to C=O/C=S groups of adjacent molecules, or solvent molecule(s) entrapped in the lattice and/or halogen atom(s) of a neighbouring SnBr4 moiety. The general range of Sn-Br distances is 2.504(3)-2.565(12) Angstrom excluding those halogen atoms directly involved in N-H ... Br-Sn interactions. These several types of intermolecular hydrogen bonding are viewed as a direct cause of ring puckering in the chelated rings approximating to a chair conformation. (C) 1998 Elsevier Science Ltd. All rights reserved.