A novel three‐dimensional copper(I) cyanide coordination polymer constructed from various bridging ligands: synthesis, crystal structure and characterization

摘要

The cyanide ligand can act as a strong σ‐donor and an effective π‐electron acceptor that exhibits versatile bridging abilities, such as terminal, μ 2 ‐ C : N , μ 3 ‐ C : C : N and μ 4 ‐ C : C : N : N modes. These ligands play a key role in the formation of various copper(I) cyanide systems, including one‐dimensional (1D) chains, two‐dimensional (2D) layers and three‐dimensional (3D) frameworks. According to the literature, numerous coordination polymers based on terminal, μ 2 ‐ C : N and μ 3 ‐ C , C , N bridging modes have been documented so far. However, systems based on the μ 4 ‐ C : C : N : N bridging mode are relatively rare. In this work, a novel cyanide‐bridged 3D Cu I coordination framework, namely poly[(μ 2 ‐2,2′‐biimidazole‐κ 2 N 3 : N 3′ )(μ 4 ‐cyanido‐κ 4 C : C : N : N )(μ 2 ‐cyanido‐κ 2 C : N )dicopper(I)], [Cu 2 (CN) 2 (C 6 H 6 N 4 )] n , (I), was synthesized hydrothermally by reaction of environmentally friendly K 3 [Fe(CN) 6 ], CuCl 2 ·2H 2 O and 2,2′‐biimidazole (H 2 biim). It should be noted that cyanide ligands may act as reducing agents to reduce Cu II to Cu I under hydrothermal conditions. Compound (I) contains diverse types of bridging ligands, such as μ 4 ‐ C : C : N : N ‐cyanide, μ 2 ‐ C : N ‐cyanide and μ 2 ‐biimidazole. Interestingly, the [Cu 2 ] dimers are bridged by rare μ 4 ‐ C : C : N : N ‐mode cyanide ligands giving rise to the first example of a 1D dimeric {[Cu 2 (μ 4 ‐ C : C : N : N )] n + } n infinite chain. Furthermore, adjacent dimer‐based chains are linked by μ 2 ‐ C : N bridging cyanide ligands, generating a neutral 2D wave‐like (4,4) layer structure. Finally, the 2D layers are joined together via bidentate bridging H 2 biim to create a 3D cuprous cyanide network. This arrangement leads to a systematic variation in dimensionality from 1D chain→2D sheet→3D framework by different types of bridging ligands. Compound (I) was further characterized by thermal analysis, solid‐state UV–Vis diffuse‐reflectance and photoluminescence studies. The solid‐state UV–Vis diffuse‐reflectance spectra show that compound (I) is a wide‐gap semiconductor with band gaps of 3.18?eV. The photoluminescence study shows a strong blue–green photoluminescence at room temperature, which may be associated with metal‐to‐ligand charge transfer.