Morrison Shaunna M, Downs Robert T, Yang Hexiong
Department of Geosciences, University of Arizona, 1040 E. 4th Street, Tucson, Arizona 85721-0077, USA.
Acta Crystallogr Sect E Struct Rep Online. 2012 Feb 1;68(Pt 2):i12-i13. doi: 10.1107/S1600536812000256. Epub 2012 Jan 11.
The crystal structure of kovdorskite, ideally Mg(2)PO(4)(OH)·3H(2)O (dimagnesium phosphate hydroxide trihydrate), was reported previously with isotropic displacement paramaters only and without H-atom positions [Ovchinnikov et al. (1980 ▶). Dokl. Akad. Nauk SSSR.255, 351-354]. In this study, the kovdorskite structure is redetermined based on single-crystal X-ray diffraction data from a sample from the type locality, the Kovdor massif, Kola Peninsula, Russia, with anisotropic displacement parameters for all non-H atoms, with all H-atom located and with higher precision. Moreover, inconsistencies of the previously published structural data with respect to reported and calculated X-ray powder patterns are also discussed. The structure of kovdorskite contains a set of four edge-sharing MgO(6) octa-hedra inter-connected by PO(4) tetra-hedra and O-H⋯O hydrogen bonds, forming columns and channels parallel to [001]. The hydrogen-bonding system in kovdorskite is formed through the water mol-ecules, with the OH(-) ions contributing little, if any, to the system, as indicated by the long H⋯A distances (>2.50 Å) to the nearest O atoms. The hydrogen-bond lengths determined from the structure refinement agree well with Raman spectroscopic data.
科夫多尔斯基石的晶体结构，理想化学式为Mg(2)PO(4)(OH)·3H(2)O（三水合二氢氧化镁磷酸盐），之前已有报道，但仅给出了各向同性位移参数且未标明氢原子位置[奥夫钦尼科夫等人（1980年▶）。苏联科学院报告。255, 351 - 354]。在本研究中，基于来自俄罗斯科拉半岛科夫多尔地块典型产地样品的单晶X射线衍射数据，重新测定了科夫多尔斯基石的结构，确定了所有非氢原子的各向异性位移参数，定位了所有氢原子且精度更高。此外，还讨论了先前发表的结构数据与报道的和计算得到的X射线粉末衍射图谱之间的不一致性。科夫多尔斯基石的结构包含一组由PO(4)四面体和O - H⋯O氢键相互连接的四个共边MgO(6)八面体，形成平行于[001]的柱体和通道。科夫多尔斯基石中的氢键体系是通过水分子形成的，OH(-)离子对该体系的贡献很小（如果有贡献的话），这由到最近O原子的长H⋯A距离（>2.50 Å）表明。从结构精修确定的氢键长度与拉曼光谱数据吻合良好。
