(2,2′-Bipyridine)chlorido[diethyl (2,2′:6′,2′′-terpyridin-4-yl)phosphonate]ruthenium(II) hexafluoridophosphate acetonitrile/water solvate

The cationic complex in the title compound, [RuCl(C10H8N2)(C19H20N3O3P)]PF6·0.83CH3CN·0.17H2O, is a water-oxidation precatalyst functionalized for TiO2 attachment via terpyridine phosphonate. The The RuII atom in the complex has a distorted octahedral geometry due to the restricted bite angle [159.50 (18)°] of the terpyridyl ligand. The dihedral angle between the least-squares planes of the terpyridyl and bipyridyl moieties is 86.04 (14)°. The mean Ru—N bond length for bipyridine is 2.064 (5) Å, with the bond opposite to Ru—Cl being 0.068 Å shorter. For the substituted terpyridine, the mean Ru—N distance involving the outer N atoms trans to each other is 2.057 (6) Å, whereas the bond length involving the central N atom is 1.944 (5) Å. The Ru—Cl distance is 2.4073 (15) Å. The P atom of the phosphonate group lies in the same plane as its adjacent pyridyl ring, with the ordinary character of the bond between P and Ctpy [1.801 (6) Å] allowing for free rotation of the terpyridine substituent around the P—Ctpy axis. The acetonitrile solvent molecule was refined to be disordered with two water molecules; occupancies for the acetontrile and water molecules were 0.831 (9) and 0.169 (9), respectively. Also disordered was the PF6 − counter-ion (over three positions) and one of the ethoxy substituents (with two positions). The crystal structure shows significant intra- and intermolecular H⋯X contacts, especially some involving the Cl− ligand.


Comment
A crucial challenge to renewable energy technologies based on artificial photosynthesis and production of solar fuels has been the development of efficient catalysts for splitting water, with evolution of H 2 and O 2 . The complete four-electron oxidation of water into dioxygen, in particular, is a semi-reaction of tremendous complexity. Recently, mononuclear ruthenium complexes such as [Ru II (OH 2 )(bpy)(tpy)] 2+ (bpy = 2,2′-bipyridine; tpy = 2,2′:6′,2"-terpyridine) and its structural analogues have emerged as catalysts for water oxidation (for example, see: Concepcion et al., 2008;Masaoka & Sakai, 2009;Tseng et al., 2008;Wasylenko et al., 2010;Yagi et al., 2011). In these systems, the catalytic aquo species is readily prepared in water by ligand substitution at the chloro precursor/precatalyst, [Ru II (Cl)(bpy)(tpy)] + (Jakubikova et al., 2009). In order to heterogenize this precatalyst by attachment onto TiO 2 surfaces, we have synthesized the title complex [Ru II (Cl)(bpy)(tpy-p)] + (I; tpy-p = diethyl 2,2′:6′,2"-terpyridine-4′-phosphonate). The phosphonate group in its diethyl ester form can then be hydrolized in acidic medium to yield its phosphonic acid, which is well known as an efficient TiO 2 anchoring group upon deprotonation. This approach has also been well demonstrated for related complexes as photosensitizers in dye-sensitized solar cells (Zakeeruddin et al., 1997). Despite the relevance of such phosphonated terpyridyl Ru complexes to these energy-related research areas, crystallographically characterized structures containing the tpy-PO 3 ligand moiety are still scarce (Zakeeruddin et al., 1997).
The hexafluorophosphate salt of I crystallized in the monoclinic space group (P2 1 /n) from an acetonitrile solution. Its crystal structure is shown in Figs. 1 and 2. The cationic complex has a distorted octahedral geometry due to the restricted bite angle of the meridionally coordinated tridendate terpyridyl ligand. The N1-Ru-N3 angle of 159.50 (18)° is very similar to those recently reported for bis-terpyridyl Ru(II) complexes (Chen et al., 2013;Jude et al., 2013), and far from the ideal angle of 180° in an octahedral geometry. The bpy ligand has a cis configuration, with the N4-Ru-N5 angle of 78.45 (19)° consistent with those typically found in Ru II -bpy complexes (Chen et al., 2011;Jude et al., 2008). The bpy-N4 atom is arranged trans to the chloride ligand in a nearly linear N-Ru-Cl fashion (172.62 (14)°). The Ru center and atoms N2, N4, N5, and Cl1 form an equatorial plane with a maximum deviation of 0.031 (4) Å from ideal planarity (N5).
The bipyridyl and terpyridyl moieties are approximately planar (with maximum deviations of 0.087 (6) Å and 0.146 (6) Å, respectively) and their mean planes are essentially perpendicular to each other with a dihedral angle of 86.04 (14)°.
For the tpy-p ligand, the mean Ru-N distance involving the outer nitrogen atoms trans to each other is 2.057 (5) Å whereas the bond distance involving the central nitrogen is much shorter (1.944 (5) Å), as a result of the structural constraint imposed by these mer-arranged tridendate ligands (Chen et al., 2013;Jude et al., 2013). For the bpy ligand, the Ru-N bond distance is 2.098 (5) Å for N5 but only 2.030 (5) for N4, reflecting the increased Ru II →N bpy π-backbonding supplementary materials sup-2 Acta Cryst. (2013). E69, m510-m511 interaction at the coordinating atom trans to the π-donor Clligand. The Ru-Cl distance of 2.4073 (15) Å is nearly the same as those observed in related structures (Jude et al., 2009). An intramolecular H···Cl contact of 2.71 Å exists between Cl1 and the hydrogen atom of the nearest C atom (H29), similar to our previous observations (Chen et al., 2011;Jude et al., 2009). Significant intermolecular contacts of 2.76 Å, 2.81 Å, and 2.85 Å betwen Cl and H3, H13, and H20 are also found, but these are closer to the sum of the van der Waals radii for hydrogen and chlorine (2.95 Å).
The P atom of the anchoring phosphonate substituent lies in the same plane as its adjacent pyridyl ring, with a maximum deviation of 0.023 (2) Å from coplanarity. The length of the formally P═O bond between P1 and O1 (1.483 (5) Å) is only about 0.06 Å shorter than that of P-O(Et) involving P1 and O2(C16H 2 C17H 3 ) and O3(C18H 2 C19H 3 ). That is partly attributed to the multiple intermolecular interactions involving these O atoms. The bond lengths and angles involving the P and O atoms are compiled along with the selected data in Table 1. The observed P1-C8 bond length of 1.801 (6) Å is typical of ordinary P-C(aromatic) bonds. As pointed earlier (Zakeeruddin et al., 1997), this ordinary character of the P-C bond allows for free rotation of the phosphonate group around the P-C tpy axis.
The acetonitrile solvate molecule was refined to be disordered with two water molecules; occupancies for the acetontrile and water molecules were 0.831 (9) and 0.169 (9), respectively. One of the ethoxy substituents (O3(C18H 2 C19H 3 )) was refined as disordered with two moieties; occupancies were 0.793 (13) and 0.207 (13). Also disordered was the PF 6counterion, which was refined over two different moieties (Figs. 1 and 2), occupancies refined to 0.726 (14) and 0.274 (14). Although classic H bonds are not found in the crystal structure of I(PF 6 )×MeCN, several intermolecular contacts (i.e., distances shorter than the sum of van der Waals radii) exist between cations (I) as well as between the cation and its counterion (PF 6 -) or solvate molecules. Those that appear to be more relevant to the crystalpacking driving forces are explicitly shown in Fig

Experimental
The synthesis of [Ru(Cl)(bpy)(tpy-p)]PF 6 was performed stepwise through a procedure involving the intermediate RuCl 2 (DMSO)(tpy-p). First, this intermediate was obtained by reacting stoichiometric amounts (1.0 mmol) of RuCl 2 (DMSO) 4 (Evans et al., 1973) with diethyl 2,2′:6′,2"-terpyridine-4′-phosphonate (Zakeeruddin et al., 1997) in 75 ml of dry EtOH/MeOH (4:1) heated at reflux for ~4 h, under an Ar atmosphere. To the intermediate product was then added 2,2′-bipyridine (20% excess) and the next step also proceeded for ~4 h, under the same conditions. The reaction solution was cooled down to room temperature and excess NH 4 PF 6 was added to form the red precipitate, which was collected by filtration and then rinsed with Et 2 O and dried under vacuum. Further purification was performed by column chromatography. The overall yield was relatively low (30%). When the same reaction was carried out in the presence of water (EtOH/H 2 O, 2:1), the partially hydrolized product (i.e. [Ru(Cl)(bpy)(tpy-P(O)(OH)(OEt))]PF 6 could be obtained in much higher yields (60%), but this product was not characterized by X-ray crystallography. For the structure of [Ru(Cl) (bpy)(tpy-p)]PF 6 reported herein, single crystals suitable for X-ray analysis were grown by slow diffusion of Et 2 O into MeCN solutions of the complex in a long thin tube.

Refinement
All carbon-bound hydrogen atom positions were idealized, and were set to ride on the atom they were attached to. An acetonitrile solvate molecule was refined to be disordered with two water molecules. C, N and O atoms of these solvate molecules were refined anisotropically without application of restraints or constraints. Water H atoms were restrained to have O-H bonding distances of 0.82 (2) Å, and intramolecular H···H distances of 1.36 Å. Occupancies for the acetontrile and water molecules refined to 0.831 (9) and 0.169 (9), respectively. One of the ethoxy substituents was refined as disordered with two moieties. Bond distances were restrained to be the same as for the not disordered ethoxy group (esd = 0.02 Å), and the P-O distances within the two disordered moieties was restrained to be the same (esd = 0.02 Å). The two oxygen atoms were constrained to have identical ADPs, the Uij components of neighboring disordered atoms were restrained to be similar (esd = 0.01 Å 2 ), and the ADPs of the methyl C atoms were restrained to be approximately isotropic (esd 0.01 Å 2 ). Occupancies refined to 0.793 (13) and 0.207 (13), respectively. The PF 6 anion was refined as disordered over two different moieties. All P-F bond distances were restrained to be similar (esd 0.02 Å), as were all intramolecular F···F distances of directly neighboring fluorine atoms. Uij components of P and F atoms were restrained to be similar, as were the components of the ADPs in the direction of the bonds (SIMU and DELU restraints in SHELXL, esd = 0.01 Å 2 for both). Occupancies refined to 0.726 (14) and 0.274 (14). The final refinement included anisotropic temperature factors on all non-hydrogen atoms.

Computing details
Data collection: APEX2 (Bruker, 2007); cell refinement: SAINT-Plus (Bruker, 2007); data reduction: SAINT-Plus (Bruker, 2007); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2013 (Sheldrick, 2008) and SHELXLE (Hübschle et al., 2011); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: publCIF (Westrip, 2010).  Two views of the crystal packing diagram of [Ru(Cl)(bpy)(tpy-p)](PF 6 )×MeCN. Nonbonded short contacts are indicated by cyan dotted lines (expanded contacts) and red dotted lines (hanging contacts). For clarity, only contacts that are structurally relevant and at least 0.1 Å shorter than the sum of van der Waals radii are shown. Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.