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(SC₆H₄^tBu)₂₄(CF₃COO)₁₈(DMF)₄]} (1) is a supertetrahedron with an inner Ag(CrO₄)₄ tetrahedron shelled by four fused Ag_11.5S₆ 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.