[CuEn3]MoO4: Synthesis, Structure, Jahn-Teller Effect, Transformations in the Range 100–1263 K

The crystal structure of [CuEn3]MoO4 (En is ethylenediamine) is studied in a range 100–390 K. The crystallographic data at 100 K are as follows: a = 27.5808(9) A, c = 9.9043(4) A, space group $$P\overline 3 $$ , V = 6524.8(4) A3, Z = 18. The coordination of copper atoms is a distorted square bipyramid. In three crystallographically independent cations. four short Cu-N distances are 2.041(2)–2.093(2) A, two long ones in a trans position are 2.397(2)–2.496(2) A (at 200 K these intervals are 2.039(4)–2.148(4) A and 2.332(2)–2.461(4) A respectively). In a range from 200 K to 298 K, the transition occurs to the space group $$P\overline 3 $$ c1 (a = 15.9992(6) A, c = 9.9385(4) A, V = 2203.17(19) A3, Z = 6) and the Cu-N distances are aligned: 2.086(6) A, 2.162(7) A, 2.273(8) A. At 390 K the Jahn-Teller effect disappears and the Cu-N distances are 2.153(4) A (a = 9.2785(14) A, c = 10.0035(18) A, $$P\overline 3 $$ 1c, V = 745.8(3) A3, Z = 2). It is shown that with increasing temperature from 100 K to 320 K the average Mo-O distances decrease from 1.766 A to 1.699 A. The ex situ powder X-ray diffraction study of the formation process of metal and carbide phases is performed during [CuEn3]MoO4 thermal decomposition in the He atmosphere in the presence of LiH. Starting from 973 K, a mixture of Mo2C and the fcc phase based on the Cu structure (a ≈ 3.65 A) forms.