Bis(2-methylanilinium) diaquabis[dihydrogendiphosphato(2−)]cobaltate(II)

In the title cobalt(II) complex with 2-methylanilinium and diphosphate, (C7H10N)2[Co(H2P2O7)2(H2O)2], a three-dimensional network is built up from anionic layers of [Co(H2P2O7)2(H2O)2]2− units and 2-methylanilinium cations located between these layers. The dihydrogendiphosphate groups present a bent eclipsed conformation, while the Co2+ ions lie on inversion centers. An intricate network of O—H⋯O and N—H⋯O hydrogen bonds is established between the different components, assuring the cohesion of the network with other interactions, being of electrostatic and van der Waals nature.


Experimental
Crystal data (C 7

Comment
Organic inorganic transition metal frameworks can be usefully employed in diverse areas, such as shape selective catalysis or adsorption (Cheetham et al., 1999;Clearfield, 1998). In such compounds the transition metal plays a key role for building interesting topologies with one-, two-or three-dimensional networks. In these atomic arrangements, the transition element is coordinated generally to ligands via several donor atoms such as oxygen or nitrogen. In recent years, many researchers have focused on diphosphates because they are powerful ligands that can link metal ions through their oxygen atoms, and can play an essential role in the interaction between the metallic centers (Xu et al., 2008).
The title compound, is built up from a diaquabis[dihydrogendiphosphato(2)]cobaltate(II) anion and two organic 2methylanilinium cations (Fig. 1). A half of the complex anion and one organic cation constitute the asymmetric unit of (I).
The metal complex anions, interconnected via hydrogen bonds involving the two hydroxyl groups of H 2 P 2 O 7 2and the water molecule, develop a thick bi-dimensional layer of formula [Co(H 2 P 2 O 7 ) 2 (H 2 O) 2 ] 2nperpendicular to the c axis ( Fig.   2). The protonated organic cations 2-CH 3 C 6 H 4 NH 3 + are anchored between these layers .
With regard to the inorganic arrangement, the Co atom is located on an inversion center and is surrounded by two symmetry related dihydrogendiphosphate ligands with a bent eclipsed conformation as seen by the P1-O4-P2 angle of 129.26 (7)% , and two water molecules in an octahedral coordination. Four external O atoms, OE, in the basal plane from two bidendate [H 2 P 2 O 7 ] groups and the two remaining O atoms, OW, in the apical positions from the water molecule give a slightly distorted CoO 6 octahedron. Within this octahedron, the Co-O distances range from 2.057 (1) to 2.149 (1) Å with Cu-OW distances longer than those of Co-OE. A similar coordination geometry around the central atom has also been observed in other M II O 6 octahedra, M II = Co or Ni, in organic diphosphate compounds (Essehli et al., 2006;Gharbi et al., 1994;Gharbi et al., 2004).

Analysis of hydrogen bonds within (I), revealed an intricate network of O-H···O and N-H···O bonds which along with
other interactions (electrostatic and Van der Waals) stabilize the whole structure. The O-H···O contacts, with O-H···O distances ranging from 2.522 (2) to 3.020 (2) Å, link the complex anions while the N-H···O bonds linking the anions and cations are weaker since the N-H···O distances are longer, ranging from 2.779 (2) to 3.105 (2) Å. These H-bonds (Table   1) participate in the cohesion of the three-dimensional network (Fig 2).

Experimental
Crystals of the title compound were prepared by adding an ethanol solution (10 ml) of 2-methylaniline (7.52 mmol) dropwise to a mixture of H 4 P 2 O 7 (3.75 mmol) and CoCl 2 (1.88 mmol) in water (20 ml). Good quality green prisms were obtained after a slow evaporation during few days at ambient temperature. The diphosphoric acid, H 4 P 2 O 7 , was produced from Na 4 P 2 O 7 by using an ion-exchange resin (Amberlite IR 120). sup-2

Bis(2-methylanilinium) diaquabis[dihydrogendiphosphato(2-)]cobaltate(II)
Crystal data (C 7   Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.