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Syntheses and Crystal Structures of a New Niobium Polysulfide K 6 Nb 4 S 22 and two New Dimorphic Tantalum Polysulfides K 6 Ta 4 S 22
Author(s) -
Stoll Petra,
Näther Christian,
Bensch Wolfgang
Publication year - 2002
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 - 10.1002/1521-3749(200211)628:11<2489::aid-zaac2489>3.0.co;2-v
Subject(s) - monoclinic crystal system , crystallography , chemistry , differential scanning calorimetry , niobium , alkali metal , crystal structure , melting point , polysulfide , group (periodic table) , transition metal , tantalum , metal , crystal (programming language) , stereochemistry , organic chemistry , electrode , electrolyte , catalysis , physics , computer science , programming language , thermodynamics
The new compounds K 6 Nb 4 S 22 and K 6 Ta 4 S 22 ( I ) have been synthesised by the reaction of NbS 2 or Ta metal in a K 2 S 3 flux. Using TaS 2 as educt a second modification of K 6 Ta 4 S 22 ( II ) is obtained. K 6 Nb 4 S 22 and K 6 Ta 4 S 22 (form I ) crystallise in the monoclinic space group C2/c with a = 35.634 (2)Å, b = 7.8448 (4)Å, c = 12.1505 (5)Å, β = 100.853 (5)°, V = 3335.8 (3)Å 3 , and Z = 4 for K 6 Nb 4 S 22 and a = 35.563 (7) Å, b = 7.836 (2)Å, c = 12.139 (2)Å, β = 100.56 (3)°, V = 3325.5 (2)Å 3 , and Z = 4 for K 6 Ta 4 S 22 ( I ). The second modification K 6 Ta 4 S 22 (form II ) crystallises in the monoclinic space group P2 1 /c with a = 7.5835 (6)Å, b = 8.7115 (5)Å, c = 24.421 (2)Å, β = 98.733 (9)°, V = 1594.6 (2)Å 3 , and Z = 2. The structures consist of [M 4 S 22 ] 6— anions composed of two M 2 S 11 sub‐units which are linked into M 4 S 22 units via terminal sulfur ligands. The anions are well separated by the K + cations. Differences between the structures of the title compounds and those with the heavier alkali cations Rb + and Cs + are caused by the different arrangement of the [M 4 S 22 ] 6— anions around the cations and the different S 2— /S 2 2— binding modes. The thermal behaviour of both modifications was investigated using differential scanning calorimetry (DSC). From these investigations there is no hint for a polymorphic transition between the two forms. After heating crystals of form II above the melting point and cooling the melt to room temperature a crystalline powder of form I can be isolated.