Tetrakis(2-amino-4-methylpyridinium) cyclo-tetra-μ2-oxido-tetrakis[dioxidovanadate(V)] tetrahydrate

The asymmetric unit of the title compound, (C6H9N2)4[V4O12]·4H2O, contains half of a [V4O12]4− anion, two 2-amino-4-methylpyridinium, (2a4mpH)+, cations and two water molecules. One water molecule is disordered over two sets of sites with equal occupancies and the H atoms for this molecule were not included in the refinement. The cation lies on an inversion center with four tetrahedral VO4 units each sharing two vertices, forming an eight-membered ring. In the crystal, the components are linked by intermolecular N—H⋯O hydrogen bonds, forming a one-dimensional network along [100]. Further stabilization is provided by weak intermolecular C—H⋯O hydrogen bonds. In addition, π–π stacking interactions with centroid–centroid distances of 3.5420 (18), 3.7577 (18) and 3.6311 (19) Å are observed.

The asymmetric unit of the title compound, (C 6 H 9 N 2 ) 4 -[V 4 O 12 ]Á4H 2 O, contains half of a [V 4 O 12 ] 4À anion, two 2amino-4-methylpyridinium, (2a4mpH) + , cations and two water molecules. One water molecule is disordered over two sets of sites with equal occupancies and the H atoms for this molecule were not included in the refinement. The cation lies on an inversion center with four tetrahedral VO 4 units each sharing two vertices, forming an eight-membered ring. In the crystal, the components are linked by intermolecular N-HÁ Á ÁO hydrogen bonds, forming a one-dimensional network along [100]. Further stabilization is provided by weak intermolecular C-HÁ Á ÁO hydrogen bonds. In addition,stacking interactions with centroid-centroid distances of 3.5420 (18), 3.7577 (18) and 3.6311 (19) Å are observed.

Comment
The chemistry of polyoxovanadate compounds are of great interest. Hybrid organo-inorganic compounds based on vanadium oxides present potential applications in catalysis, electron conductivity, magnetism and photochemistry (Paredes-García et al., 2008). The VO 4 group is an important building block of many polynuclear species. A well known example is the V 4 O 12 4ring which has an eight-membered ring structure formed by four VO 4 tetrahedra sharing vertices (Nakano et al., 2002). The complexing ability of the V 4 O 12 4ion with transition metal ions is of great interest and the ring takes part as a ligand (Paredes-García et al., 2008). Herein we report the crystal structure of the title compound obtained as a side product from a reaction of ammonium vanadate, cobalt nitrate, boric acid and 2-Amino-4-methylpyridine.
The asymmetric unit of the title compound, (2a4mpH) 4 (V 4 O 12 ).4H 2 O, comprises a half of a V 4 O 12 4anion, two (2a4mpH) + cations and two solvent molecules of water ( Fig. 1). One molecule of water is disordered over two positions (O7 and O8) with equal occupancies.
The V 4 O 12 4ion is centrosymmetric with four tetrahedral VO 4 units which share two vertices with each other to form an eight-membered ring. The 2-Amino-4-methylpyridine molecule is protonated via its endocyclic nitrogen atom. In the crystal, extensive intermolecular N-H···O hydrogen-bonding interactions (Table 1) between cations, anions and solvent water molecules form 1-D motive chains along [100] (Fig.2). The crystal packing is defined by a layered structure in which chains involving 2a4mpH + and V 4 O 12 4ions are associated via π-π stacking interactions between the aromatic rings of (2a4mpH) + cations into layers parallel to (110) (Fig. 3).

Experimental
Ammonium vanadate, cobalt nitrate hexahydrate, boric acidand 2-amino-4-methylpyridine (in molar ratio 0.5:1:1:2) were dissolved in H 2 O (50ml). The reaction mixture was placed in a Parr-Teflon lined stainless steel vessel. It was sealed and heated at 443K for 48 h. The reaction mixture was gradually cooled to room temperature. Pale yellow crystals were isolated from solution.

Refinement
A water molecule is disordered over two positions (O7 and O8) with equal occupancies. The H atoms for this molecule were not located nor were they included in the refinement. They are however, included in the molecular formula. Hydrogen atoms bound to the water molecule O9 were refined using the following restraints: O-H bond length 0.95 (2) Å and H···H