Bis(2,2′:6′,2′′-terpyridine)ruthenium(II) bis(perchlorate) hemihydrate

The asymmetric unit of the title compound, [Ru(C15H11N3)2](ClO4)2·0.5H2O, contains one ruthenium–terpiridine complex cation, two perchlorate anions and one half-molecule of water. Face-to-face and face-to-edge π-stacking interactions between terpyridine units [centroid–centroid distances = 3.793 (2) and 3.801 (2)  Å] stabilize the crystal lattice The partially occupied water molecule interacts with two perchlorate ions via O—H⋯O hydrogen bonds. In the crystal lattice, the complex cations, perchlorate ion-water pairs and the second perchlorate anions are arranged into columns along b direction.

The asymmetric unit contains one divalent cation of the ruthenium-terpiridine complex, two perchlorate anions and a water molecule with a half-occupancy (Fig. 1). The crystal lattice is stabilized by terpyridine moieties and respective face-to-face and face-to-edge π-stacking interactions. The partially occupied water molecule and one perchlorate anion are located in a proximity of the inversion center and a symmetry related water-anion pair is generated. Two hydrogen bonds O5-H5A···O1A and H5-H5B···O2A (equivalent anion -x + 2,-y + 1,-z) are formed between water molecule and oxygen atoms of perchlorate units. Geometrical parameters of hydrogen bond interactions are summarized in Table 1. In the crystal lattice each water molecule serves as a bridge between two symmetry dependent perchlorate units (Fig. 2). It is of note, that only one perchlorate unit and its symmetry-mates form hydrogen bonds with water molecules, whereas the second anion interacts with C-bonded hydrogen atoms (Fig 2).

Experimental
The transition metal complex salt, [Ru II (tpy) 2 ](ClO 4 ) 2 was prepared according to the procedure described by Burstall et al. (1952). Crystals suitable for X-ray diffraction study were obtained at room temperature by a slow evaporation of [Ru II (tpy) 2 ](ClO 4 ) 2 solution in acetonitrile.

Refinement
During the initial refinement steps, the occupancy factor for the water molecule was refined and it was in a range of 0.49-0.52. For the final refinement cycles, this occupancy was fixed at 0.5 with isotropic atomic displacement parameters for hydrogen atoms. All H atoms were located in electron density difference maps. C-bonded hydrogen atoms were constrained to idealized positions with C-H distances fixed at 0.95 Å and 1.2U eq (C). O-H distances were fixed at 0.85 Å with U iso (H) = 1.5U eq (C) and the positions of water hydrogen atoms were refined.

Figure 1
The molecular structure of the compound. Displacement ellipsoids are drawn at the 50% probability level.   Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. 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 R-factors(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ.