Organic Templated Cuprous Cyanide Open Frameworks Based on Cu2(CN)6 Dimer with Strong and Long-Lived Luminescence

Abstract

By using environmental friendly K3[Fe(CN)6] as a cyanide source, hydrothermal reactions of CuCl2 and diamines resulted in four Cu2(1,1,2-μ3-CN)2(CN)4 dimer-based organic templated cuprous cyanide open frameworks, namely, [H1.5mepip]2[Cu4(CN)7] (1), [H1.5etpip]2[Cu4(CN)7] (2), [H2me2pip][Cu3(CN)5] (3), and [H2dmpa][Cu4(CN)6] (4) (mepip = N-methylpiperazine; etpip = N-ethylpiperazine, me2pip = N,N-dimethylpiperazine, dmpa = 3-dimethyl-aminopropylamine). Isomorphic 1 and 2 show three-dimensional (3-D) (4,6)-connected FeS2-like open frameworks constructed by 4-connected Cu(CN)4 monomers and 6-connected Cu2(CN)6 dimers. Complex 3 shows an unprecedented 3-D (4,6)-connected open framework in which the ratio of 4-connected Cu(CN)4 monomers to 6-connected Cu2(CN)6 dimers is 1:1. Complex 4 shows a 3-D (3,6)-connected AgIn2-like open framework constructed by 3-connected Cu(CN)3 monomers and 6-connected Cu2(CN)6 dimers. Different from CuCN/amine coordination polymers, the protonated organic diamines in 1–4 act as templates in the formation of cuprous cyanide open frameworks. Even at ambient temperature, 1, 2, 3, and 4 show strong blue-green photoluminescence related to Cu2(CN)6 dimer, which is mainly assigned to metal-to-ligand charge-transfer (MLCT) by time-dependent density functional theory (TD-DFT) and electronic band structure calculations.