Structure
Copper cyanide is a coordination polymer. It exists in two polymorphs both of which contain -- chains made from linear copper(I) centres linked by cyanide bridges. In the high-temperature polymorph, HT-CuCN, which is isostructural with AgCN, the linear chains pack on a hexagonal lattice and adjacent chains are off set by +/- 1/3 c, Figure 1. In the low-temperature polymorph, LT-CuCN, the chains deviate from linearity and pack into rippled layers which pack in an AB fashion with chains in adjacent layers rotated by 49 °, Figure 2.
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Figure 1: The structure of HT-CuCN showing the chains running along the c axis. Key: copper = orange and cyan = head-to-tail disordered cyanide groups.
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Figure 2: The structure of LT-CuCN showing sheets of chains staking in an ABAB fashion. Key copper = orange and cyan = head-to-tail disordered cyanide groups.
LT-CuCN can be converted to HT-CuCN by heating to 563 K in an inert atmosphere. In both polymorphs the copper to carbon and copper to nitrogen bond lengths are ~1.85 Å and bridging cyanide groups show head-to-tail disorder.
Read more about this topic: Copper(I) Cyanide
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