Crystal structure of catena-poly[[[(2-ethoxypyrazine-κN)copper(I)]-di-μ2-cyanido] [copper(I)-μ2-cyanido]]

The title compound, {[Cu(EtOpz)(CN)2][CuCN]}n, where EtOpz is 2-ethoxypyrazine, is a two-dimensional polymeric copper complex with different coordination environments of the two CuI ions. One Cu atom is coordinated to the 2-ethoxypyrazine molecule and two bridging cyanide ligands, equally disordered over two sites. The second Cu atom is coordinated by two disordered over two sites bridging cyanide groups. Two copper–cyanide chains are connected through Cu⋯Cu contact.


Supramolecular features
The crystal packing of the title compound ( Fig. 2) consists of two types of orthogonal polymeric chains (the first involving the Cu1 atoms and parallel to the c axis and the second involving the Cu2 atoms and parallel to the b axis) interconnected by CuÁ Á ÁCu contacts and forming two-dimensional layers parallel to (100) A view normal to the ac plane of the crystal structure of the title compound, showing the CuÁ Á ÁCu contacts as dashed lines. 2-Ethoxypyrazine rings (except for the N atoms connected to Cu1) and H atoms have been omitted for clarity. Colour code: Cu green, N blue and CN group magenta. Table 1 Hydrogen-bond geometry (Å , ).

Database survey
A search of the Cambridge Structural Database (CSD, Version 5.39, last update November 2017; Groom et al., 2016) confirmed that the structure of the title complex has not been reported previously and revealed for the fragment -C N-Cu-C N-and an azine ligand attached to Cu (unsubstituted, substituted and fused azines) 128 structures, which are polymeric copper cyanide chains decorated with various co-ligands. Most of these co-ligands are derivatives of pyridine, piperidine, methylenetetramine and piperazine. In particular, the structure of catena-[pentakis( 2 -cyano)tris(1phenylpiperazine)pentacopper] (refcode VIYPOK; Pike et al., 2014) contains five independent Cu atoms and five nonsymmetrically disordered cyanides, and forms two independent one-dimensional chain sublattices, i.e. (CuCN)(PhPip) and (CuCN) 3 (PhPip), associated by CuÁ Á ÁCu pairwise cupro-philic interactions, with distances of 2.5586 (10) and 2.6441 (10) Å . A search of the CSD for two C-N-Cu-C-N fragments with a defined CuÁ Á ÁCu distance less than 2.8 Å gave 80 hits, among which is an example close to the title structure, i.e. catena-[( 2 -N-benzylpiperazine-N,N 0 )tetrakis( 2cyano)tetracopper(I)] (refcode LOGWIO; Lim et al., 2008), where the resulting network is composed of planar rows of undulating CuCN chains running roughly parallel to the a axis and crosslinked by bridging benzylpiperazine ligands in the c direction, forming two-dimensional double sheets capped by nonbridging ligands. Two CuÁ Á ÁCu interactions are present in the mentioned coordination polymer, with distances of 2.6650 (6) and 2.9644 (6) Å .

Synthesis and crystallization
Crystals of the title compound were obtained by slow diffusion within three layers in a 3 ml glass tube. The first layer was a solution of K[Cu(CN) 2 ] (7.7 mg, 0.05 mmol) in 1 ml of H 2 O, the second layer was a H 2 O/EtOH mixture (1:1 v/v, 1 ml) and the third layer was a solution of 2-ethoxypyrazine (3.1 mg, 0.025 mmol) in 0.5 ml of EtOH. After two weeks, colourless block-shaped crystals had formed in the middle layer. The crystals were kept under the mother solution prior to measurement.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. All H atoms were placed geometrically and refined as riding, with C-H = 0.93 Å and U iso (H) = 1.2U eq (C) for aromatic hydrogens, C-H = 0.97 Å and U iso (H) = 1.2U eq (C) for the CH 2 group, and C-H = 0.96 Å and U iso (H) = 1.5U eq (C) for the CH 3 group. A rotating model was used for the methyl group. All cyano ligands are disordered over two sites with occupancies of 0.5. The coordinates of C and N atoms sharing the same sites and their displacement ellipsoids were constrained to be the same.

Funding information
Funding for this research was provided by: Ministry of Education and Science of Ukraine (grant Nos. 19BF037-01M, 19BF037-04 and 19BF037-01).

catena-Poly[[[(2-ethoxypyrazine-κN)copper(I)]-di-µ 2 -cyanido] [copper(I)-µ 2 -cyanido]]
Crystal data Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.