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Dimorphism of K 4 Ta 2 S 11 : Syntheses, Crystal Structures, and Properties of two Alkali Metal Tantalum Sulfides
Author(s) -
Herzog Sabine,
Näther Christian,
Bensch Wolfgang
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(199906)625:6<969::aid-zaac969>3.0.co;2-o
Subject(s) - triclinic crystal system , orthorhombic crystal system , crystallography , chemistry , lattice energy , tantalum , crystal structure , bond length , alkali metal , organic chemistry
The new ternary potassium tantalum polysulfide K 4 Ta 2 S 11 crystallizing in the triclinic space group P1 with a = 7.465(2), b = 11.441(3), c = 11.534(3) Å, α = 68.66(2), β = 86.59(2) and γ = 83.09(2)° represents a second modification of the already known orthorhombic form, space group Pca2 1 with a = 13.166(2), b = 7.449(2) and c = 18.000(2) Å. The interatomic distances and angles within the Ta 2 S 11 4– anions of both forms are very similar, but significant differences are observed for the S…S distances between neighboured anions. Temperature dependent single crystal X‐ray experiments yield thermal expansion coefficients of 9.88(30) and 9.44(4) 10 –5 K –1 for the triclinic and orthorhombic compound, respectively. The higher density for the orthorhombic form indicates that this modification is the thermodynamical more stable form at low temperatures. This assumption is supported by calculations of the electrostatic contributions to the lattice energies using MAPLE (Madelung part of lattice energy). The lattice energy of the orthorhombic form is about 46 kJ mol –1 larger than that of the triclinic modification. Small differences are observed in the MIR (Medium Infrared Range) spectra of the two dimorphs which correlate well with the slightly different Ta = S bond lengths within the Ta 2 S 11 4– anions. The compounds were also characterized using UV/Vis reflectance spectroscopy.