Crystal structure of tetrakis[μ-3-carboxy-1-(1,2,4-triazol-4-yl)adamantane-κ2 N 1:N 2]tetrafluoridodi-μ2-oxido-dioxidodisilver(I)divanadium(V) tetrahydrate

The crystal structure of the title compound is based on the molecular heterobimetallic unit {Ag2(VO2F2)2(tr)4} supported by the 1,2,4-triazole ligand, 1-(1,2,4-triazol-4-yl)-3-carboxyadamantane.


Chemical context
Heterometallic hybrids incorporating a metal oxide/ oxofluoride matrix are of particular interest as they exhibit non-trivial magnetic, luminescent (Cui et al., 2012), optical and catalytic properties (Dolbecq et al., 2010). Among the broad range of inorganic anions, vanadium oxofluorides (VOFs) stand out for their large number of types and structural motifs from mono- (Aldous et al., 2007;Stephens et al., 2005) to polynuclear (Buchholz et al., 1988;Ninclaus et al., 1997) ones in the structure as discrete units or incorporated into coordination frameworks (Welk et al., 2007;Mahenthirarajah et al., 2008). The Ag I /VOF pair is a non-typical combination for classical coordination chemistry, but materials such as Ag 4 V 2 O 6 F 2 (Sorensen et al., 2005;Albrecht et al., 2009) and Ag 3 VO 2 F 4 (Chamberlain et al., 2010) are attractive electrochemically active phases for solid-state batteries.
In the present research we introduce a new ligand [tr-ad-COOH = 1-(1,2,4-triazol-4-yl)-3-carboxyadamantane], whose 1,2,4-triazole and -COOH donor groups can support the formation of the Ag-V heterometallic coordination cluster. It has recently been shown (Senchyk et al., 2012) that symmetrical 1,2,4-triazoles can selectively bridge these different metals. Considering a possible step-by-step mechanism, it becomes clear that after the formation of the simplest {Ag 2 ( 2tr) 2 (tr) 2 } 2+ binuclear fragment, two N atoms remain uncoordinated and have potential for further interactions. In aqueous reaction media, vanadium oxofluorides exist in anionic forms with weakly coordinated water molecules that are very labile ISSN 2056-9890 toward N-donor ligand substitution. Thus, a combination of an Ag I -triazole cation and VOF anions lead to the neutral tetranuclear {Ag I 2 (V V O 2 F 2 ) 2 (tr) 4 } unit, which was found in the structure of the title [Ag 2 (VO 2 F 2 ) 2 (tr-ad-COOH) 4 ]Á4H 2 O complex I (Fig. 1).

Structural commentary
The asymmetric unit of the title compound contains one Ag I cation, one [VO 2 F 2 ] À anion, two organic ligands and two solvent water molecules. Two silver ions, two VOF anions and four tr-ad-COOH units constitute the molecular tetranuclear cluster, which resides across an inversion centre (Fig. 1) (Addison et al., 1984) of 0.72 (for strict square-pyramidal polyhedra = 0 and for trigonal-bipyramidal = 1).

Supramolecular features
The structure of I is characterized by an extended hydrogenbonding network. The carboxylic function of the tr-ad-COOH ligand remains in a neutral form, being uncoordinated. It is involved in hydrogen bonding that leads to a three-dimensional hydrogen-bonded network (   The molecular structure of compound I, showing the atomic labelling scheme [symmetry code: (i) -x, 1 -y, -z]. Displacement ellipsoids are drawn at the 30% probability level. The two symmetry-generated water molecules are omitted. hydrogen-bonding interactions is shown in Fig. 4. The corresponding geometric parameters are given in Table 2. One carboxylic group, as a hydrogen-bond donor, forms a contact with a water molecule O3-H1OÁ Á ÁO2W iv = 2.650 (4) Å [symmetry code: (iv) x, 1 + y, z], while another COOH group, as a hydrogen-bond acceptor, is directed toward the F atom of a {VO 2 F 2 } anion [O5-H2OÁ Á ÁF1 v = 2.589 (3) Å ; symmetry code: (v) 1 + x, À1 + y, z]. Two water molecules are interbonded [O2W-H3WÁ Á ÁO1W = 2.753 (4) Å ] and additionally act as hydrogen-bond donors with O and F atoms from the neighboring {VO 2 F 2 } anions and as hydrogen-bond acceptor (in the case of O2W ) with the O3 atom from an adjacent carboxylic group. Some weak contacts between the triazole C-H groups and F atoms of the VOF anions are also observed.
The adamantyl scaffolds are shown in a stick mode omitting the H atoms [symmetry codes:

Figure 3
Projection on the ab plane showing the crystal packing in the structure.
Vanadium oxofluoride anions are shown as polyhedra.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. The non-H atoms were refined with anisotropic displacement parameters and a soft rigidbond restraint was applied to C10-C13 in order to improve the refinement stability. C-bound hydrogen atoms were positioned geometrically and refined as riding, with C-H = 0.93 Å (triazole), C-H = 0.97 Å (adamantane CH 2 ), C-H = 0.98 Å (adamantane CH) and with U iso (H) = 1.2U eq (C). O-bound hydrogen atoms were located in a difference-Fourier map and then refined with O-H = 0.82 Å (carboxylic) or 0.85 Å (H 2 O) with U iso (H) = 1.5U eq (O). program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: WinGX (Farrugia, 2012). 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.