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-dimension al (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-(CuCl)-Cl-I)(NMP), L-NHC = a carbene form of L) was obtained; Im-MOF-3 is iso-structural with Im-MOF-1 except that its organic linker has an N-heterocyclic carbene (NHC) copper(I) complex (L-NHC-(CuCl)-Cl-I). 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.