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Structure Determination of a Low Temperature Phase of Calcium and Strontium Amide by means of Neutron Powder Diffraction on Ca(ND 2 ) 2 and Sr(ND 2 ) 2
Author(s) -
Senker J.,
Jacobs H.,
Müller M.,
Press W.,
Mayer H. M.,
Ibberson R. M.
Publication year - 1999
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/(sici)1521-3749(199912)625:12<2025::aid-zaac2025>3.0.co;2-3
Subject(s) - neutron diffraction , crystallography , strontium , chemistry , amide , monoclinic crystal system , tetragonal crystal system , ionic bonding , ion , crystal structure , powder diffraction , organic chemistry
Calcium and Strontium amide are ionic compounds crystallising in a tetragonally distorted anatase structure‐type at ambient temperatures. The amide ions (NH 2 – /ND 2 – ) resemble water molecules in structure and in charge distribution. By means of temperature dependent neutron diffraction investigations weak super‐structure reflections were observed at temperatures below 90 K (Ca(ND 2 ) 2 ) and 60 K (Sr(ND 2 ) 2 ), respectively, indicating the existence of a so far unknown low‐temperature (LT) phase. Using high resolution neutron powder diffraction at temperatures below 10 K the structure was determined for both compounds. The LT‐phases are isotypic and crystallise monoclinic in the space group P2 1 /c with four formula units within the unit cell: Ca(ND 2 ) 2 at 10 K a = 7.257(2) Å, b = 7.2434(2) Å, c = 6.300(1) Å, β = 124.73(1)° Sr(ND 2 ) 2 at 5 K a = 7.6950(1) Å, b = 7.68374(9) Å, c = 6.6324(3) Å, β = 124.917(2)°. Their structure is closely related to the tetragonal HT‐phase, but an ordering of the amide ions occurs due to freezing of a lattice mode which is dominated by the librational motion of the amide ions in the {1 0 0} planes of the HT‐phase.