• journal_title：The Canadian Mineralogist
• Contributor：Zhi-Biao Hu ; Cheng-Xin Wang ; Chang-Qing Tong ; Ya-Xi Huang ; Yuanming Pan ; Jin-Xiao Mi
• Publisher：Mineralogical Association of Canada
• Date：2013-04-01
• Format：text/html
• Language：en
• Identifier：10.3749/canmin.51.2.223
• journal_abbrev：Can Mineral
• issn：0008-4476
• volume：51
• issue：2
• firstpage：223
• section：Articles

Synthetic gengenbachite, KH<sub>8sub>(Fe<sub>2.66sub>Al<sub>0.34sub>)(PO<sub>4sub>)<sub>6sub>·6H<sub>2sub>O, has been prepared hydrothermally at 423–393 K. Single-crystal X-ray structure refinements (R<sub>1sub> = 0.035 for 1838 [I > 2σ(I)] unique reflections and wR<sub>2sub> = 0.083 for all 1863 reflections) confirm that gengenbachite crystallizes in the trigonal space group P31c (No. 159) and is isotypic with synthetic (NH<sub>4sub>) H<sub>8sub>Fe<sup>3+sup><sub>3sub>(PO<sub>4sub>)<sub>6sub>·6H<sub>2sub>O. The crystal structure consists of [FeO<sub>6sub>] octahedra and [PO<sub>4sub>] tetrahedra forming a three-dimensional framework with eight-membered-ring channels running along the [100], [010], and [110] directions. All but one hydrogen atom have been located to allow description of the hydrogen bonds in gengenbachite. Magnetic susceptibility analysis of gengenbachite yielded the Curie constant C = 12.07 emu·K·mol<sup>−1sup> and the Weiss constant θ<sub>Psub> = −58.9 K. The effective magnetic moment per Fe atom μ<sub>effsub> = 6.03 μ<sub>Bsub> provides further support for high-spin Fe<sup>3+sup> in octahedral coordination.