On the low temperature modifications of Ag6Si2O7 and Ag6Ge2O7 - Synthesis, crystal structure, and comparison of Ag-Ag distances

For the first time, single crystals of Ag6Si2O7 and Ag6Ge2O7 have been obtained by solid state reactions of the binary oxides at temperatures of 350 degrees C while applying oxygen pressures of 700 bar. According to the results of X-ray crystal structure determinations both compounds crystallize isostructural in P2(1) (Ag6Si2O7: a = 5.3043(5) Angstrom, b = 9.7533(7) Angstrom, c = 15.9283(13) Angstrom, beta = 91.165(8)degrees, 3881 independent reflections, R1 = 3.3%, wR2 = 7.2%; Ag6Ge2O7: a = 5.3713(4) Angstrom, b = 9.9835(8) Angstrom, c = 16.2249(14) Angstrom, beta = 90.904(8)degrees, 2111 independent reflections, R1 = 4.3%, wR2 = 6.0%, Z = 4). The crystal structures contain two independent M(2)O(7)(6-) anions, one in a staggered, and the other in an ecliptic conformation. The cationic partial structure may be described as a distorted bcc arrangement of Ag+ and M(4+). Comparison of the structures with respect to the Ag-Ag separations reveals the latter to be probably due to intrinsic d(10)-d(10) bonding interactions as far as the range of 2.89 Angstrom to 3.25 Angstrom is considered.