General Assembly of Twisted Trigonal-Prismatic Nonanuclear Silver(I) Clusters

A general class of C-3-symmetric Ag-9 clusters, [Ag9S(tBuC(6)H(4)S)(6)(dpph)(3)(CF3SO3)] (1), [Ag-9(tBuC(6)H(4)S)(6)(dpph)(3)(CF3SO3)(2)]CF3SO3 (2), [Ag-9(tBuC(6)H(4)S)(6)(dpph)(3)(NO3)(2)] NO3 (3), and [Ag-9(tBuC(6)H(4)S)(7)(dpph)(3)(Mo2O7)(0.5)](2)2CF(3)COO (4) (dpph=1,6-bis(diphenylphosphino)hexane), with a twisted trigonal-prism geometry was isolated by the reaction of polymeric {(HNEt3)(2)[Ag-10(tBuC(6)H(4)S)(12)]}(n), 1,6-bis(diphenylphosphino)hexane, and various silver salts under solvothermal conditions. The structures consist of discrete clusters constructed from a girdling Ag-9 twisted trigonal prism with the top and bottom trigonal faces capped by diverse anions (i.e., S2- and CF3SO3- for compound 1, 2xCF(3)SO(3)(-) for compound 2, 2xNO(3)(-) for compound 3, and tBuC(6)H(4)S(-) and Mo2O72- for compound 4). This trigonal prism is bisected by another shrunken Ag-3 trigon at its waist position. Interestingly, two inversion-related Ag-9 trigonal-prismatic clusters are dimerized by the Mo2O72- ion in compound 4. The twist is amplified by the bulkier thiolate, which also introduces high steric-hindrance for the capping ligand, that is, the longer dpph ligand. Four more silver-sulfur clusters (namely, compounds 5-8) with their nuclearity ranging from 6-10 were solely characterized by single-crystal X-ray diffraction to verify the above-described synergetic effect of mixed ligands in the construction of Ag-9 twisted trigonal prisms. Surprisingly, only cluster 1 emits yellow luminescence at =584nm at room temperature, which may be attributed to a charge transfer from the S 3p orbital to the Ag 5s orbital, or mixed with metal-centered (MC) d(10)d(9)s(1) transitions. Upon cooling from 300 to 80K, the emission intensity was enhanced along with a hypsochromic shift. The good linear relationship between the maximum emission intensity and the temperature for compound 1 in the range of 180-300K indicates that this is a promising molecular luminescent thermometer. Furthermore, cyclic voltammetric studies indicated that the diffusion- and surface-controlled redox processes were determined for compounds 1 and 3 as well as compound 4, respectively.