Synthesis, Crystal Structure and Magnetic Property of Disodium Biscarbonato-cobaltate(Ⅱ) Tetrahydrate, Na2Co(CO3)2·4H2O
ZHENG Yue-Qing, YE Yu-Han, HU Fu-Tao, PETERS Karl, von SCHNERING Hans Georg
1999, 15(4):
311-316.
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The title compound, Na2Co(CO3)2·4H2O, was synthesized by dropwise addition of 1.0 mLof 1 mol/L Co(CH3COO)2 to 50 mL of aqueous solution containing 7.0 g(66.0 mmol) of Na2CO3 and 2.5 g(29.8 mmol) of NaHCO3 under stirring. A rose colored rhombohedral crystal grew by the slow evaporation of the solution of the title compoud at room temperature. The crystal structure was established on the basis of the single crystal X-ray diffraction data. Na2Co(CO3)2·4H2O crystallizes in the monoclinic space group C2/c with a =0.8566(1) nm, b =0.7146(1) nm, c = 1.4387(2) nm, β =97.59(1)°, V =0.8730(2) nm3, Dx=2.260 g/cm3, F (000)=596, Mr=296.99, μ (Mo Kα)=21.06 cm-1, Z =4 and the final R(F) =0.032 and wR(F2) =0.068 on the basis of 947 reflections ( F2 ≥ 2σ(F02)). The crystal consists of H2O molecules, Na+ ions and 2D∞2[Co(CO3)2]2- layers extending parallel to (001). H2O molecules and Na+ cations are located between the 2D layers. Each Co atom is tetrahedrally coordinated by four O atoms from four CO32- groups with d (Co—O)=0.2065(2) nm, 0.2076(2) nm and the angle of O—Co—O is in the range of 97.7(1)°—128.5(1)°. The CO32- group bridging two Co atoms via two O atoms deviates from D3h symmetry with d (C—O)=0.1272(3)—0.1299(3) nm and the angle of O—C—O is in the range of 119.5(2)°—1.23.4(2)°. Each Na atom, with two close Na neighbours at 0.3384(2) nm and 03467(2) nm, respectively, is octahedrally coordinated by six O atoms from four H2O molecules and two carbonate groups belonging to two layers with d (Na—O)=0.2327(2)—0.2411(2) nm. Of two crystallographically different H2O molecules, one forms hydrogen bonds to two CO32- groups of one 2D layer, and the other to those from two different 2D layers. Na2Co(CO3)2·4H2O is antiferromagnetic below 16 K, and between 30—300 K its magnetic behaviour obeys Curie Weiss law χm(cm3·mol-1)=2.625/( T -12.1) with μeff =4.5 B.M. at 298 K.
