Synthetic control of coincidental formation of an N-heterocyclic carbene–copper(i) complex and imidazolium cations within metal–organic frameworks

Abstract

By changing the concentration of copper salt (Cu(ClO₄)₂), a two-dimensional (2D) copper paddle-wheel-based metal–organic framework (MOF) containing an imidazolium unit (Im-MOF-1 with a framework formula of [Cu^II(L)(NMP)](ClO₄), L = 1,3-bis(4-carboxyphenyl)imidazolium and NMP = N-methyl-2-pyrrolidone) and a 3D MOF (Im-MOF-2, Cu^II(L)(H₂O)) with aqua-bridged Cu ions as inorganic infinite secondary building units were respectively prepared. With CuCl as a copper source, another square-grid 2D MOF (Im-MOF-3, Cu^II(L_NHC–Cu^ICl)(NMP), L_NHC = a carbene form of L) was obtained; Im-MOF-3 is isostructural with Im-MOF-1 except that its organic linker has an N-heterocyclic carbene (NHC) copper(I) complex (L_NHC–Cu^ICl). Density functional theory modeling calculations show that the NHC–CuCl complex in the organic linker of Im-MOF-3 retains the electronic properties of its molecular form, as evidenced by molecular orbital analysis.