X-ray structural analysis of the dinitratotetrapyridinecopper(II) complex and its clathrates with tetrahydrofuran and chloroform

The structure of the [CuPy4(NO3)2] complex (Py = pvridine) and its clathrates with tetrahydrofuran and chloroform (both with a host:guest molar ratio of 1:2) were determined by the single-crystal XRD method (CAD-4 diffractometer, CuKα radiation, graphite monochromator). The three structures are molecular, with van der Waals intermolecular contacts. The main structural parameters of the [CuPy4(NO3)2] molecule are preserved in the clathrates. The coordination octahedron of copper(II) consisting of four nitrogen atoms of the pyridine ligands and two oxygen atoms of the monodentate nitrate groups in the transposition is severely distorted due to the lengthened Cu-0 bonds (2.46-2.61 å). In the complex phase, the pyridine rings of the molecule are nearly perpendicular to the equatorial plane, whereas in the clathrates the molecule has a propeller conformation. The clathrates are isomorphous with each other and with other compounds of the general formula [MPy4X2]-2G. Close relationship between the structural types of the [MPy4X2]-2G clathrates is revealed. The anomalous stability of [CuPy4(NO3)2] compared to the analogous Mn, Co, Ni, Zn, and Cd complexes, which can only exist in clathrate form, is explained.