Tripyridinium cis-tetrachloridodioxidomolybdate(VI) chloride

In the title compound, (C5H6N)3[MoCl4O2]Cl, the pyridinium cations are N—H⋯Cl hydrogen bonded to the anionic [MoCl4O2]2− complexes and to the two crystallographically independent chloride anions (located on C2 axes). The Mo6+ centre adopts a highly distorted octahedral geometry, being surrounded by four chloride and two terminal oxide groups. The oxide ligands are mutually cis.

In the title compound, (C 5 H 6 N) 3 [MoCl 4 O 2 ]Cl, the pyridinium cations are N-HÁ Á ÁCl hydrogen bonded to the anionic [MoCl 4 O 2 ] 2À complexes and to the two crystallographically independent chloride anions (located on C2 axes). The Mo 6+ centre adopts a highly distorted octahedral geometry, being surrounded by four chloride and two terminal oxide groups. The oxide ligands are mutually cis.
We wish to thank Dr Martyn Pillinger (CICECO, University of Aveiro) and Dr André D. Lopes (University of the Algarve) for their collaboration in the preparation of this communication. We are also grateful to Fundaçã o para a Ciê ncia e a Tecnologia (FCT, Portugal) for their general financial support, for the post-doctoral research grant SFRH/BPD/63736/2009 (to JAF), SFRH/BPD/25269/2005 (to SG), SFRH/BD/45116/ 2008 (to SF) and for specific funding toward the purchase of the single-crystal diffractometer. We also wish to thank the Associated Laboratory CICECO for a research grant to AG.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: SJ5018).   teiro et al., 2010;Gago et al., 2009;Pereira et al., 2007;Cunha-Silva et al., 2007;Bruno et al., 2007). During our recent efforts to coordinate pyridine to the molybdenum centre, we have isolated the title compound: Remarkably, a search in the literature and in the Cambridge Structural Database (Allen, 2002) reveals the existence of only one other structure with the [MoCl 4 O 2 ] 2anion (Luan et al., 2008).
The asymmetric unit of the title compound I is composed of three pyridinium (PyH) cations whose charge is bal-  Table 1].
The PyH cations are engaged in strong and relatively directional N + -H···Clhydrogen bonds with the chloride anions (not shown; Table 2). We note that N3 is interacting with two spatially close chloro ligands (Cl3 and Cl4), forming a R 1 2 (4) graph set motif (Grell et al.,1999) typical of bifurcated interactions. The crystal packing is, thus, mediated by the need to effectively fill the available space ( Figure 2) since no significant supramolecular contacts are present in the crystal structure (e.g., C-H···O or C-H···Cl contacts are all greater than 3.18 Å).

Experimental
Chemicals were purchased from commercial sources and were used as received without purification.
To an aqueous solution (30 ml) of HCl (3.3 mol dm -3 ) containing 2.0 g (8.3 mmol) of Na 2 MoO 4 . 2H 2 O, a solution of pyridine (1.34 ml, 16.6 mmol) in CH 2 Cl 2 (60 ml) was slowly added dropwise. The biphasic mixture was vigorously stirred for 3 h at ambient temperature. The aqueous phase was separated and washed three times with CH 2 Cl 2 , and then allowed to evaporate yielding a solid. Crystals of the title compound were ultimately isolated by slow diffusion of diethyl ether into a concentrated solution in acetonitrile.

Refinement
Hydrogen atoms bound to carbon and nitrogen were located at their idealized positions and were included in the final structural model in riding-motion approximation with: C-H = 0.95 Å (aromatic) and N-H = 0.88 Å. The isotropic thermal displacement parameters for these atoms were fixed at 1.2 times U eq of the respective parent atom.
A total of 4490 estimated Friedel pairs have not been merged and were used as independent data for the structure refinement. The Flack parameter (Flack, 1983) converged to 0.03 (4), ultimately assuring a correct absolute structure determination from the single-crystal data set. Fig. 1. Schematic representation of the asymmetric unit. The [MoCl 4 O 2 ] 2anion has a highly distorted {MoCl 4 O 2 } octahedral coordination environment, and the anions Cl5 and Cl6 are located on C2 axes. Thermal ellipsoids are drawn at the 50% probability level. For selected bond lengths (in Å) and angles (in degrees) see Table 1.