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

Abstract

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 tBuC6H4S-, SiBu-, and SiPr- consist of three core-shells, an inner CrO42-, an intermediate Ag-S aggregate and finally the protective organic moieties. {(HNEt3)3[Ag(CrO4)4@Ag46(SC6H4tBu)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(SiBu)27(CF3COO)3]n (2) is an undulated snake-like tube housing the infinite CrO42- tetrahedra. [(CrO4)2@Ag41(SiBu)30(NO3)3(CN)4]n (3) forms an uncommon 7-connected kwh network incorporating hexagonal layers of Ag19(SiBu)15 balls with a single inner CrO42- connected by another Ag atom. Both enantiomeric chiral qtz frameworks of [CrO4@Ag20(SiPr)10(Cr2O7)2(COOCF3)4(DMF)4]n (4) were structurally characterized. In 4, Cr2O72- connects the Ag20(SiPr)10 clusters with a trapped CrO42- into a 3D quartz (qtz) structure, where the spherical cluster acts like oxygen and Cr2O72- 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.