supplementary materials

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 2-methylanilinium 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 H₂P₂O₇^2- and the water molecule, develop a thick bi-dimensional layer of formula [Co(H₂P₂O₇)₂(H₂O)₂]^2n- perpendicular to the c axis (Fig. 2). The protonated organic cations 2-CH₃C₆H₄NH₃⁺ 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 [H₂P₂O₇] groups and the two remaining O atoms, OW, in the apical positions from the water molecule give a slightly distorted CoO₆ 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^IIO₆ 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).