Acta Crystallographica Section C

Crystal Structure Communications

Volume 65, Part 8 (August 2009)

metal-organic compounds

su3035 scheme

Acta Cryst. (2009). C65, m279-m283 [ doi:10.1107/S0108270109023968 ]

Bis(1,3,4-trimethylpyridinium) tetrachloridocuprate(II) and bis(1,3,4-trimethylpyridinium) tetrabromidocuprate(II): an examination of the A₂CuX₄ Fdd2 structure type

M. R. Bond

Abstract: The title bis(1,3,4-trimethylpyridinium) tetrahalidocuprate(II) structures, (C₈H₁₂N)₂[CuCl₄], (I), and (C₈H₁₂N)₂[CuBr₄], (II), respectively, consist of flattened [CuX₄]^2- tetrahedral complex anions and planar 1,3,4-trimethylpyridinium cations. Chloride compound (I) is a rare example of an A₂CuCl₄ structure with an elongated unit cell in the polar space group Fdd2. The [CuCl₄]^2- anions have twofold rotational symmetry and are arranged in distorted hexagonal close-packed (hcp) layers, which are interleaved with layers of cations, each in a four-layer repeat sequence, to generate the elongated axis. The organic cations stack along [101] or [10 $\overline{1}$ ] in alternating layers. The methyl groups meta on the cation ring and the larger of the trans Cl-Cu-Cl angles both face the same direction along the polar axis and are the most prominent features determining the polarity of the structure. Bromide compound (II) crystallizes in a centrosymmetric structure with a similar layer structure but with only a two-layer repeat sequence. Here, symmetry-inequivalent cations are segregated into alternating layers with cations, forming hcp layers of inversion-related cation pairs in one layer and parallel stacks of cations in the other. The change in space group when the larger Br^- ion is present suggests that the 1,3,4-trimethylpyridinium ion has a minimal size to allow the Fdd2 A₂CuX₄ structure type.

Formula: (C₈H₁₂N)₂[CuCl₄] and (C₈H₁₂N)₂[CuBr₄]


	Structure factor file (CIF format) (149.3 kbytes) [ doi:10.1107/S0108270109023968/su3035Isup2.hkl ] Contains datablock I

	Structure factor file (CIF format) (243.3 kbytes) [ doi:10.1107/S0108270109023968/su3035IIsup3.hkl ] Contains datablock II

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