Synchrotron powder diffraction data is presented for the monoclinic polymorph of dimethylarsinic acid, (CH3)2AsO(OH) (DMAV). Rietveld refinement with GSASII yielded lattice parameters of a = 15.9264(15) Å, b = 6.53999(8) Å, c = 11.3401(9) Å, and β = 125.8546(17)° (Z = 8, space group C2/c). The Rietveld-refined structure was compared with both a density functional theory (DFT)-optimized structure and the published, low-temperature single-crystal structure, and all three structures exhibited excellent agreement. The triclinic polymorph of DMAV was also DFT optimized with CRYSTAL17 to determine the positions of the hydrogen atoms. Monoclinic DMAV forms zigzag chains parallel to the b-axis with adjacent DMAV molecules connected by an O–H⋯O bond, whereas triclinic DMAV forms dimers connected by two O–H⋯O bonds.

中文翻译：

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二甲基胂酸 (CH3)2AsO(OH) 的粉末 X 射线衍射数据

提供了二甲基胂酸的单斜晶型多晶型物的同步加速器粉末衍射数据，（CH3)2AsO(OH) (DMA五）。使用 GSASII 进行 Rietveld 细化产生的晶格参数为一种= 15.9264(15) 埃，b= 6.53999(8) 埃，C= 11.3401(9) Å，和β= 125.8546(17)° (Z= 8，空间群C2/C）。将 Rietveld 精制结构与密度泛函理论 (DFT) 优化结构和已发表的低温单晶结构进行比较，所有三种结构都表现出极好的一致性。DMA的三斜晶型五还用 CRYSTAL17 优化了 DFT 以确定氢原子的位置。单斜DMA五形成锯齿形链平行于乙-具有相邻 DMA 的轴五分子通过 O-H⋯O 键连接，而三斜晶系 DMA五形成由两个 O-H⋯O 键连接的二聚体。