Ammonothermal Synthesis,X-Ray and Time-of-Flight Neutron Crystal-Structure Determination,and Vibrational Properties of Barium Guanidinate,Ba(CN3H4)2 |
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Authors: | Dr Sebastian Benz Dr Ronja Missong George Ogutu Dr Ralf P Stoffel Prof Dr Ulli Englert Dr Shuki Torii Dr Ping Miao Prof Dr Takashi Kamiyama Prof Dr Richard Dronskowski |
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Institution: | 1. Chair of Solid-State and Quantum Chemistry, Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1, 52056 Aachen, Germany;2. Institute of Materials Structure Science & J-PARC Center, High Energy Accelerator Research Organization (KEK), School of High Energy Accelerator Science, Sokendai, 203-1, Tokai-mura, Ibaraki, 319-1106 Japan |
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Abstract: | We report the crystal structure of Ba(CN3H4)2 as synthesized from liquid ammonia. Structure solution based on X-ray diffraction data suffers from a severe pseudo-tetragonal problem due to extreme scattering contrast, so the true monoclinic symmetry is detectable only from neutron powder diffraction patterns, and structure solution and refinement was greatly aided by density-functional theory. The symmetry lowering is due to slight deviations of the guanidinate anion from the mirror plane in space group P b2, a necessity of hydrogen bonding. At 300 K, barium guanidinate crystallizes in P21/c with a=6.26439(2) Å, b=16.58527(5) Å, c=6.25960(2) Å, and a monoclinic angle of β=90.000(1)°. To improve the data-to-parameter ratio, anisotropic displacement parameters from first-principles theory were incorporated in the neutron refinement. Given the correct structural model, the positional parameters of the heavy atoms were also refinable from X-ray diffraction of a twinned crystal. The two independent guanidinate anions adopt the all-trans- and the anti-shape. The Ba cation is coordinated by eight imino nitrogens in a square antiprism with Ba−N contacts between 2.81 and 3.04 Å. The IR and Raman spectra of barium guanidinate were compared with DFT-calculated phonon spectra to identify the vibrational modes. |
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Keywords: | barium X-ray diffraction neutron diffraction vibrational spectroscopy density-functional theory |
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