Structure, solution assembly, and electroconductivity of nanosized argento-organic-cluster/framework templated by chromate.

In view of elucidating potential structures and assembly mechanism of silver clusters and silver cluster-based metal-organic frameworks, we prepared four argento-organic-clusters/frameworks where the structures were directed by chromate in the presence of different thiolates. All four structures with (t)BuC6H4S(-), S(i)Bu(-), and S(i)Pr(-) consist of three core-shells, an inner CrO4(2-), an intermediate Ag-S aggregate and finally the protective organic moieties. {(HNEt3)3[Ag(CrO4)4@Ag46(SC6H4(t)Bu)24(CF3COO)18(DMF)4]} (1) is a supertetrahedron with an inner Ag(CrO4)4 tetrahedron shelled by four fused Ag11.5S6 lobes. [(CrO4)5@Ag40(S(i)Bu)27(CF3COO)3]n (2) is an undulated snake-like tube housing the infinite CrO4(2-) tetrahedra. [(CrO4)2@Ag41(S(i)Bu)30(NO3)3(CN)4]n (3) forms an uncommon 7-connected kwh network incorporating hexagonal layers of Ag19(S(i)Bu)15 balls with a single inner CrO4(2-) connected by another Ag atom. Both enantiomeric chiral qtz frameworks of [CrO4@Ag20(S(i)Pr)10(Cr2O7)2(COOCF3)4(DMF)4]n (4) were structurally characterized. In 4, Cr2O7(2-) connects the Ag20(S(i)Pr)10 clusters with a trapped CrO4(2-) into a 3D quartz (qtz) structure, where the spherical cluster acts like oxygen and Cr2O7(2-) takes the place of Si in SiO2. Electrospray ionization mass spectrometry (ESI-MS) analysis of the reaction solutions of 1-4 clearly indicated that (i) the Ag(CrO4)4@Ag46 core of 1 can retain its molecular structure in the solution and (ii) the chromate-templated polynuclear silver-thiolate species in solution are important building blocks to construct the 1D or 3D motif for 2-4. The electrochemistry in sulfuric acid and enhancement of the electrical conductivity upon I2 doping have also been reported.