An infinite two-dimensional hybrid water–chloride network in a 4′-(furan-2-yl)-2,2′:6′,2′′-terpyridine nickel(II) matrix

An unprecedented two-dimensional water–chloride anionic {[(H2O)10Cl2]2−}n network has been structurally identified in a hydrophobic matrix of the nickel(II) complex [Ni(ftpy)2]Cl2·10H2O [ftpy = 4′-(furan-2-yl)-2,2′:6′,2′′-terpyridine].


Chemical context
Water has received much scientific interest as it is a major chemical constituent on the earth's surface and it is also the source of life. Many discrete water clusters and polymeric water aggregates, with different types of hydrogen bonds and in diverse sizes and shapes, captured in the crystal lattice of an organic or metal coordination complex during crystallization have been found and investigated experimentally and theoretically (Dutta et al., 2015;Ganguly & Mondal, 2015;Han et al., 2014;Hundal et al., 2014;Pati et al., 2014).

Figure 2
View of the hydrophobic (represented by wireframes) and hydrophilic (represented by spheres) layers in 1.

Figure 3
A view of the two-dimensional undulating sheet of hydrophobic layers,  Fig. 4). Both the OÁ Á ÁO and OÁ Á ÁCl distances are comparable with those found in various types of water clusters and water-chloride associates (Safin et al., 2015;Bhat & Revankar, 2016;Ris et al., 2016). The resulting twodimensional network can be considered as a set of alternating cyclic fragments with three tetranuclear, three pentanuclear, one hexanuclear and two octanuclear fragments, as shown in Fig. 5a. Two of these fragments are composed only of water molecules, whereas the other seven rings are water-chloride hybrids with one or two Cl À anions. Most of the rings are nonplanar, contributing to the formation of an intricate relief geometry of the water-chloride layer. Using the method described by Infantes and co-workers (Infantes & Motherwell, 2002;Infantes et al., 2003), this two-dimensional waterchloride network can be described as having an L4(6)4(6)4(6)5(5)5(6)5(6)6(8)8(8)8(10) pattern.
NiCl 2 Á6H 2 O (0.1 mmol, 0.024g) and ftpy (0.2 mmol, 0.060 g) were dissolved in 10 ml distilled water and 10 ml methanol. The solution was left alone for slow evaporation without disturbance for about one month and reddish brown crystals of (1) suitable for X-ray analysis were obtained. A view of the hybrid water-chloride hydrogen-bonded assemblies in 1, with water molecules and chloride anions shown as coloured balls and hydrogen bonds as dashed lines. Table 2 Hydrogen-bond geometry (Å , ).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. All hydrogen atoms except those of water molecules were generated geometrically and refined isotropically using a riding model, with C-H = 0.93 Å and U iso (H) = 1.2U eq (C). The hydrogen atoms of solvent water molecules were located in difference-Fourier maps, refined with DFIX restraints of O-H distances and finally fixed at those positions using AFIX 3 in SHELXL (Sheldrick, 2015b). Atoms C36, C37, C38 and O2 were found to be disordered over two sets of sites with a refined occupancy ratio of 0.786 (13):0.214 (13) for C36/C36A, C37/C37A, C38/C38A, and O2/O2A. In order to model the disorder of this furyl ring, various restraints (DFIX, FLAT, ISOR, DELU, EADP) were applied in the refinement.  program(s) used to solve structure: SHELXT (Sheldrick, 2015a) and OLEX2 (Dolomanov et al., 2009); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015b) and OLEX2 (Dolomanov et al., 2009); molecular graphics: DIAMOND (Brandenburg & Putz, 2008); software used to prepare material for publication: publCIF (Westrip, 2010 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.

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