Crystal structure and physical properties of anhydrous sodium copper carbonate

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Abstract
The crystal structure of the title compound has been established by single-crystal X-ray diffraction methods from photographic data. The structure was solved by conventional Patterson and Fourier heavy-atom methods and refined by block-diagonal least-squares techniques to R 0·11 for 286 independent reflections. Crystals are monoclinic, space group p21/a, with Z= 2 in a unit cell with dimensions : a= 6·18(2), b= 8·19(2), c= 5·64(2)Å, β= 116·2(2)°. The asymmetric unit is one half of the formula unit. The structure consists of copper atoms occupying special positions of symmetry , co-ordinated by four planar oxygen atoms [Cu–O(1) 1·95(1); Cu–O(2) 1·90(1)Å, O(1)–Cu–O(2) 88·7(5)°), the distortion from the exact square plane not being significant. The copper atoms are bridged by, but not coplanar with, carbonate groups in an infinite two-dimensional polymeric puckered sheet in the ab plane, successive sheets being interleaved by sodium ions. The carbonate ions, although planar, are significantly distorted, the non-co-ordinated bond being much shorter [C–O(3), 1·22(2)Å) than the other two (C–O(1), 1·36(2); C–O(2), 1·29(2)Å]. The i.r. spectrum displays splittings providing supporting evidence for distorted stereochemistries of the CuO4 and CO3 groups, the metal–oxygen and carbon–oxygen asymmetric stretching modes being appreciably split, and possibly characteristic of the bridging carbonate group. The magnetic moment of 1·92 ± 0·04 BM over the temperature range 100—400 K is consistent with the requirements of square planar co-ordinated copper(II) and is indicative of little or no copper–copper interaction (CuCu, 4·89 Å).

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