Dimetal Linked Open Frameworks:  [(CH₃)₄N]₂(Ag₂,Cu₂)Ge₄S₁₀

Abstract

Synthetic and X-ray structural details, optical and vibrational spectroscopic, and thermal properties of the materials [(CH 3 ) 4 N] 2 M 2 Ge 4 S 10 (where M = Cu, Ag), are described for the first time. Rietveld PXRD full-profile structure refinements of [(CH 3 ) 4 N] 2 M 2 Ge 4 S 10 reveal a novel open-framework architecture in which dimetal M 2 2+ and adamantanoid Ge 4 S 10 4 - building blocks are alternately substituted into the tetrahedral Zn 2+ and S 2 - sites of a zinc blende lattice, all linked together by [Ge(μ-S)] 2 M−M[(μ-S)Ge] 2 metal−metal bonded bridging units. The metal−metal distances in the S 2 M−MS 2 “twisted I” dihedral unit are 2.761 Å (Ag) and 2.409 Å (Cu). These internuclear separations are shorter than the bulk metals themselves (2.89 Å, Ag; 2.54 Å, Cu). This implies that the adamantanoid Ge 4 S 10 4 - -based open-framework structure is held together by d 10 −d 10 M + −M + metal−metal bonds. FT-Raman provides a direct probe of this interaction. Dimetal-framework breathing vibrational modes are observed around 38 cm - 1 for M = Ag and 55 cm - 1 for M = Cu. In situ VT-PXRD analysis demonstrates that [(CH 3 ) 4 N] 2 Ag 2 Ge 4 S 10 retains its structural integrity upon exposure to air after in vacuo heating above the [(CH 3 ) 4 N] + loss temperature. It seems likely that the disilver connection of adamantanoid Ge 4 S 10 4 - building blocks confers thermal stability upon the framework.