The First Crystallographic and Spectroscopic Characterization of a 3<i>d</i>-Metal Borohydride: Mn(BH<sub>4</sub>)<sub>2</sub> Radovan Černý Nicolas Penin Hans Hagemann Yaroslav Filinchuk 10.1021/jp9015883.s003 https://acs.figshare.com/articles/journal_contribution/The_First_Crystallographic_and_Spectroscopic_Characterization_of_a_3_i_d_i_Metal_Borohydride_Mn_BH_sub_4_sub_sub_2_sub_/2855392 The first crystal structure of a 3<i>d</i>-metal borohydride is presented. Solvent-free homoleptic manganese borohydride Mn(BH<sub>4</sub>)<sub>2</sub> forms at ambient conditions in ball-milled mixtures of alkali metal borohydrides and MnCl<sub>2</sub>. It crystallizes in the trigonal crystal system with the space group symmetry <i>P</i>3<sub>1</sub>12 and is stable from 90 to 450 K, where the compound melts. Thermal expansion of Mn(BH<sub>4</sub>)<sub>2</sub> between 90 and 400 K is highly anisotropic and strongly nonuniform. The structure of Mn(BH<sub>4</sub>)<sub>2</sub> shows interesting similarity to α-Mg(BH<sub>4</sub>)<sub>2</sub>: the two structures are made of similar layers L with the composition <i>M</i><sub>4</sub>(BH<sub>4</sub>)<sub>10</sub> per cell. The layers are stacked along the <i>c</i>-axis, and rotated by 120° by the 3<sub>1</sub> axis in Mn(BH<sub>4</sub>)<sub>2</sub> and by 60° by the 6<sub>1</sub> axis in α-Mg(BH<sub>4</sub>)<sub>2</sub>. Three identical layers are stacked along one unit cell vector <i>c</i> in Mn(BH<sub>4</sub>)<sub>2</sub>, while six layers are stacked in α-Mg(BH<sub>4</sub>)<sub>2</sub>. In Mn(BH<sub>4</sub>)<sub>2</sub> the layers L are connected directly, and share atoms. In α-Mg(BH<sub>4</sub>)<sub>2</sub> the layers L are intercalated by a thin layer L′, which contains one Mg atom per layer per cell. The layer L is chiral, and both borohydrides crystallize in chiral space groups. Similar to α-Mg(BH<sub>4</sub>)<sub>2</sub>, the structure of Mn(BH<sub>4</sub>)<sub>2</sub> is not densely packed and contains isolated voids with the estimated volume of 21 Å<sup>3</sup> each, which occupy in total 6% of the space. The resemblance between Mn(BH<sub>4</sub>)<sub>2</sub> and α-Mg(BH<sub>4</sub>)<sub>2</sub> is also reflected in their Raman and infrared spectra. 2009-05-21 00:00:00 alkali metal borohydrides layers L space group symmetry P 3112 chiral space groups Mg Mn Å3 unit cell vector c