Hexakis(4-acetylpyridinium) octadecachloridotetraantimonate(III)

The title compound, (C7H8NO)6[Sb4Cl18], contains centrosymmetric hexaanions built up from four vertex-sharing alternating SbCl5 square-based pyramids and highly distorted SbCl6 octahedra when long (<3.2 Å) ‘secondary’ Sb—Cl interactions are taken into account. The inter-polyhedral Sb—Cl bonds define a square-shape. In the crystal, the components are linked by N—H⋯Cl, C—H⋯Cl and C—H⋯O hydrogen bonds, generating a three-dimensional network.

The title compound, (C 7 H 8 NO) 6 [Sb 4 Cl 18 ], contains centrosymmetric hexaanions built up from four vertex-sharing alternating SbCl 5 square-based pyramids and highly distorted SbCl 6 octahedra when long (<3.2 Å ) 'secondary' Sb-Cl interactions are taken into account. The inter-polyhedral Sb-Cl bonds define a square-shape. In the crystal, the components are linked by N-HÁ Á ÁCl, C-HÁ Á ÁCl and C-HÁ Á ÁO hydrogen bonds, generating a three-dimensional network.

Comment
As a continuation of our study of phase transition materials, including organic ligands (Li et al., 2008), metal-organic coordination compounds (Zhang et al., 2009), organic-inorganic hybrids, we studied the dielectric properties of the title compound, unfortunately, there was no distinct anomaly observed from 93 K to 400 K, (m.p. 421-423 K), suggesting that this compound should be not a real ferroelectrics or there may be no distinct phase transition occurred within the measured temperature range. In this article, the crystal structure of (I) has been presented. 4-Acetylpyridine may be used as a ligand in coordination compounds e.g. with Zn (Steffen & Palenik, 1977) or Ni (Pang et al., 1994). The crystal structures of 4-acetylpyridine together with inorganic acids are also known e.g. with sulfuric acid (Fu, 2009b) and perchloric acid (Fu, 2009a).
The cell unit of the title compound is made up of six almost planar protonated 4-acetylpyridinium cations and a [Sb 4 Cl 18 ] 6anion ( Fig. 1.).In the coordinate anion of [Sb 4 Cl 18 ] 6-, antimony(III) atoms have two kinds of coordination pattern. Sb 3+ (2) coordinated with five Cl ions construct a distorted tetragonal pyramidal structure, composing two briding and three terminal Cl atoms. There are Cl-Sb secondary bonds by the linkage between the Sb 3+ (1)···Cl5 and Sb 3+ (1)···Cl6, with the bond lengths of these secondary bonds 3.0210 (11)Å and 3.1280 (11) Å, respectively, compared to the normal coordination bonds of Sb-Cl 2.3516 (12)Å to 2.8937 (11) Å. Owing to these secondary bonds, the coordination number of the central ion Sb 3+ (1) increases to six, and it adopts a distorted octahedral geometry.
The tridimensional network arrangement in the crystal structure of (I) is mainly determined by relatively strong and directional hydrogen bonds (Table. 1), Experimental 2.28 g (10 mmol) SbCl 3 was firstly dissolved in 10 ml 1:1 HCl solution, to which 2.42 g (20 mmol) 4-acetylpyridine ethanol solution was then added under stirring. Hydrochloric acid was added until the precipitated substrates disappeared. The acid solution was allowed to slowly evaporate at room temperature until colorless prisms of (I) were grown.

Refinement
Positional parameters of all the H atoms were calculated geometrically and were allowed to ride on the C and N atoms to which they are bonded, with U iso (H) = 1.2U eq (C), U iso (H) = 1.2U eq (N). Fig. 1. The molecular structure of (I) with displacement ellipsoids drawn at the 30% probability level (all H atoms have been omitted for clarity). Unlabelled atoms are generated by the symmetry operation (2-x, 1-y, 1-z).