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 [(CH3)4N]2M2Ge4S10 (where M = Cu, Ag), are described for the first time. Rietveld PXRD full-profile structure refinements of [(CH3)4N]2M2Ge4S10 reveal a novel open-framework architecture in which dimetal M22+ and adamantanoid Ge4S104- building blocks are alternately substituted into the tetrahedral Zn2+ and S2- sites of a zinc blende lattice, all linked together by [Ge(μ-S)]2M−M[(μ-S)Ge]2 metal−metal bonded bridging units. The metal−metal distances in the S2M−MS2 “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 Ge4S104--based open-framework structure is held together by d10−d10 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 [(CH3)4N]2Ag2Ge4S10 retains its structural integrity upon exposure to air after in vacuo heating above the [(CH3)4N]+ loss temperature. It seems likely that the disilver connection of adamantanoid Ge4S104- building blocks confers thermal stability upon the framework.