METAL BETAINE INTERACTIONS .3. CRYSTAL-STRUCTURES OF POLYMERIC DIAQUABIS(BETAINE)DISILVER(I) DINITRATE AND BIS(PYRIDINE BETAINE)DISILVER(I) DIPERCHLORATE

Two polymeric silver(I) complexes of betaine (Me3N+CH2CO2-, L1) and pyridine betaine (C5H5N+CH2CO2-, L2) have been prepared and characterized by X-ray crystallography. The complexes [{Ag2L2(1)(H2O)2(NO3)2}n] 1 and [{Ag2L2(2)(ClO4)2}n] 2 are structurally similar, being composed of centrosymmetric carboxylato-bridged Ag2(carboxylato-O,O')2 dimers (Ag-O 2.21-2.41 angstrom) which are extended into a 'stairs-like' polymer through the co-ordination of each metal centre by a carboxylate oxygen atom [Ag-O 2.47-2.50 angstrom] from an adjacent dimer. In addition, the primary co-ordinating sphere about the silver atom is completed by an aqua ligand [Ag-O 2.554(3) angstrom] in complex 1 and by a perchlorate oxygen atom [Ag-O 2.415(3) angstrom] in 2. The intra-dimer Ag ... Ag distance is 2.898(1) for 1 and 2.814(2) angstrom for 2, the latter being one of the shortest among known dinuclear silver(I) carboxylates.