| Popis: |
The nickel arsenatotungstate K10[As2W19(H2O){Ni(H2O)}2O67]·18H2O (1) has been synthesized. Due to its instability in water, attempts to obtain crystals of 1 suitable for X-ray diffraction have failed. The stabilization of the [As2W19(H2O){Ni(H2O)}2O67]10− core has been reached by synthesizing the analogue mixed {CsK} salt. The crystal structure of Cs6K2[Ni(H2O)6][As2W19(H2O){Ni(H2O)}2O67]·17H2O (2) has been resolved. It consists of two [α-AsW9O33]9− sub-units linked via a belt containing a tungsten and two nickel cations. Comparison of infrared and electronic absorption spectroscopic data for 1 and 2 has confirmed the structure proposed for 1. The instability of 1 led us to investigate the behavior of 1 in water. UV–Vis spectroscopy revealed that the formation of this complex is a multi-step reaction. An intermediate, the complex K8[Ni(H2O)6]1.5[As2W19(H2O){K(H2O)}{Ni(H2O)4}O67]·21H2O (3), has been isolated and characterized by elemental analysis, UV–Vis and infrared spectroscopies, and X-ray diffraction. In 3, the two vacant sites of the [As2W19O67]14− anion are occupied by a nickel and a potassium, forming a {WNiK} belt. It follows that the stability of 2 in water is due to the large ionic radius of Cs+, which prevents the inclusion of the alkaline cation into the cavity of the [As2W19O67]14− anion. The complex 3 represents a unique example of a fully characterized intermediate leading to the formation of a sandwich-type polyoxometalate. |
Full Text from ScienceDirect