Copper(I) Cyanide Coordination Polymers Constructed from Bis(Pyrazole-1-yl)alkane Ligands: Observation of the Odd−Even Dependence in the Structures

The mixture of CuCl2·2H2O and K3[Fe(CN)6] reacts with a series of flexible bis(pyrazole-1-yl)alkane ligands, Pz-(CH2)n-Pz (n = 1 for bpzm, n = 2 for bpze, n = 3 for bpzp, and n = 4 for bpzb), under hydrothermal conditions to produce four new copper(I) cyanide complexes: {[Cu2(CN)2(bpzm)]}n (1), {[Cu2(CN)2(bpze)]}n (2), {[Cu2(CN)2(bpzp)]}n (3), and {[Cu(CN)(bpzb)]}n (4), respectively. The X-ray analyses reveal that 1 exhibits a novel three-dimensional (3D) honeycomb-like framework, 2 shows a 2-fold interpenetration two-dimensional (2D) network, 3 exhibits a 3D structure, and 4 forms a 2D grid-like structure. An interesting odd−even phenomenon is observed in the complexes: when n is odd (n is the number of the CH2 spacer of ligands), the resulting complex exhibits a 3D framework, whereas when n is even, a 2D structure is generated. It could be explained that the numbers have a close relationship with dihedral angles among pyrazole rings of the ligands which have a great effect on the structures. Luminescent properties of the four complexes have been investigated in the solid state and 1 and 3 exhibit strong emissions, while 2 and 4 generate weak or no emission.