The effect of MX anions (M = Al, Ga, In, Tl; X = Cl, Br, I) on the structures of their tetra-N-butylammonium salts

Author： Rudawska-Frąckiewicz K. Siekierski S.

ISSN： 0095-8972

Source： Journal of Coordination Chemistry, Vol.57, Iss.9, 2004-06, pp. : 777-784

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Abstract

In order to study the effect of MX anions on the structures of Bu₄N[MX₄] salts (M = Al, Ga, In, Tl; X = Cl, Br, I) the crystal structures of Bu₄N[AlBr₄] (1), Bu₄N[TlCl₄] (2) and Bu₄N[TlBr₄] (3) have been determined by single-crystal X-ray diffraction. The three salts crystallize in the orthorhombic system, the space group Pnna, Z = 4. The cell dimensions are: (1) a = 18.624(11), b = 11.724(8), c = 11.679(7) Å, V = 2549.9 Å³; (2) a = 18.473(12), b = 1.680(8), c = 11.548(3)Å, V = 2491.6 Å³ and (3) a = 18.656(7), b = 11.918(8), c = 11.804(5) Å, V = 2624.5 Å³. The structures consist of distorted tetrahedral MX anions and Bu₄N⁺ cations. In the tetrahedral AlBr, TlCl and TlBr anions there are always two pairs of M-X distances: 2.25(1), 2.29(1); 2.391(4), 2.395(5); and 2.531(2), 2.537(3) Å, respectively. Comparison of the existing data on the structures of Bu₄N[MX₄] salts shows that: (1) for each group 13 element from Al to Tl the significantly greater increase in M-X distance on passing from Br to I than from Cl to Br results in a change of symmetry from Pnna to P2₁/n and in a greater distortion of the tetrahedron; (2) the increase in the M-X distance when Br is substituted for Cl, or I for Br, is independent of M, which suggests that for a given X atom the character of the M-X bond is the same, irrespective of the central M atom.