Structural Transformations of [CuEn3]WO4 Complex Salt in the Range 100–390 K and Its Degradation to [CuEn2](WO4)·2H2O

The crystal structure of [CuEn3]WO4 (En is ethylenediamine) is studied in the temperature range 100–390 K. Crystallographic data at 100 K are: a = 27.6903(8) A, c = 9.9405(3) A, space group P3, V = 6600.8(4) A3, Z = 18. Copper atomic coordination is a distorted square bipyramid. Four short Cu–N distances are within 2.038(5)–2.110(6) A; two long distances are within 2.374(8)–2.514(7) A. The lengths of N–H…O interionic contacts lie within 1.96–2.17 A. A temperature elevation makes the Cu–N distances equal: at 298 K they are within 2.066(2)–2.256(3) A(a = 16.0391(8) A, c = 9.9608(6) A, space group P3c1, V = 2219.1(3) A3, Z = 6), and at 390 K they are 2.151(6) A(a = 9.2986(10) A, c = 10.0520(14) A, P31c, V = 752.7(2) A3, Z = 2). In the range from 100 K to 390 K the average W–O distances decrease from 1.776 A to 1.734 A. Hirshfeld surfaces of complex cations are analyzed. It is shown that with increasing temperature the number of interionic N–H…O contacts decreases. The [CuEn3]WO4 phase is found to be unstable and on storing in air it transforms into [CuEn2](WO4)·2H2O.