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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 4building blocks are alternately substituted into the tetrahedral Zn 2+ and S 2sites 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 4building blocks confers thermal stability upon the framework.

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