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

Abstract

By using environmental friendly K 3 [Fe(CN) 6 ] as a cyanide source, hydrothermal reactions of CuCl 2 and diamines resulted in four Cu 2 (1,1,2-μ 3 - CN) 2 (CN) 4 dimer-based organic templated cuprous cyanide open frameworks, namely, [H 1.5 mepip] 2 [Cu 4 (CN) 7 ] ( 1 ), [H 1.5 etpip] 2 [Cu 4 (CN) 7 ] ( 2 ), [H 2 me 2 pip][Cu 3 (CN) 5 ] ( 3 ), and [H 2 dmpa][Cu 4 (CN) 6 ] ( 4 ) (mepip = N -methylpiperazine; etpip = N -ethylpiperazine, me 2 pip = N, N -dimethylpiperazine, dmpa = 3-dimethyl-aminopropylamine). Isomorphic 1 and 2 show three-dimensional (3-D) (4,6)-connected FeS 2 -like open frameworks constructed by 4-connected Cu(CN) 4 monomers and 6-connected Cu 2 (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 Cu 2 (CN) 6 dimers is 1:1. Complex 4 shows a 3-D (3,6)-connected AgIn 2 -like open framework constructed by 3-connected Cu(CN) 3 monomers and 6-connected Cu 2 (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 Cu 2 (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.