New mixed-valence chromium structure type : NH4Cr(CrO4)(2)

• Synthesis and crystal structure of a new structure type of mixed Cr(III)/Cr(VI) chromates is reported. NH4Cr(CrO4)(2) was prepared from CrO3 in the presence of (NH4)(2)Ce(NO3)(6). Since this is the first preparation of mixed valence ternary chromium oxides from aqueous solution, a reaction pathway for this synthesis is suggested. The crystal structure of NH4Cr(CrO4)2 has been determined from three-dimensional X-ray data collected at low temperature, 173 K. The structure belongs to the orthorhombic space group Pnma, with a = 14.5206(10), b = 5.4826(4), c = 8.7041(7) angstrom and Z = 4. The title compound consists of corner-sharing chromium(III) octahedra and chromium(VI) tetrahedra forming a three-dimensional network with the composition [Cr(CrO4)(2]n)(n-), containing channels in which zigzag rows of ammonium ions balance the net charge.

Ämnesord

NATURVETENSKAP  -- Kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences (hsv//eng)

NATURVETENSKAP  -- Kemi -- Oorganisk kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Inorganic Chemistry (hsv//eng)

Nyckelord

NH4Cr3O8

mixed-valence ternary oxide

mixed-valence chromate

Cr(VI)/Ce(III) redox reaction

X-ray diffraction

Chemistry

Kemi

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