fac-Triaqua(1,10-phenanthroline-κ2 N,N′)(sulfato-κO)cobalt(II): crystal structure, Hirshfeld surface analysis and computational study

The CoII atom in the title complex is octahedrally coordinated within an N2O4 donor set defined by two N-atom donors of the 1,10-phenanthroline ligand, sulfate-O and three aqua-O atoms, the latter occupying an octahedral face. In the crystal, supramolecular layers parallel to (110) are sustained by aqua-O—H⋯O(sulfate) hydrogen bonding.

The Co II atom in the title complex, [Co(SO 4 )(C 12 H 8 N 2 )(H 2 O) 3 ] (or C 12 H 14 CoN 2 O 7 S), is octahedrally coordinated within a cis-N 2 O 4 donor set defined by the chelating N-donors of the 1,10-phenanthroline ligand, sulfate-O and three aqua-O atoms, the latter occupying an octahedral face. In the crystal, supramolecular layers lying parallel to (110) are sustained by aqua-O-HÁ Á ÁO(sulfate) hydrogen bonding. The layers stack along the c-axis direction with the closest directional interaction between them being a weak phenanthroline-C-HÁ Á ÁO(sulfate) contact. There are four significant types of contact contributing to the calculated Hirshfeld surface: at 44.5%, the major contribution comes from O-HÁ Á ÁO contacts followed by HÁ Á ÁH (28.6%), HÁ Á ÁC/CÁ Á ÁH (19.5%) and CÁ Á ÁC (5.7%) contacts. The dominance of the electrostatic potential force in the molecular packing is also evident in the calculated energy frameworks. The title complex is isostructural with its manganese, zinc and cadmium containing analogues and isomeric with its mertriaqua analogue.

Chemical context
As a consequence of their ability to link metal ions in a variety of different ways, polynitrile anions, either functioning alone or in combination with neutral co-ligands, provide opportunities for the generation of molecular architectures with varying dimensions and topologies (Benmansour et al., 2012). The presence of other potential donor groups such as those derived from -OH, -SH or -NH 2 , together with their rigidity and electronic delocalization, mean that polynitrile anions can also lead to new magnetic and luminescent coordination polymers based on transition-metal ions (Benmansour et al., 2010;Kayukov et al., 2017;Lehchili et al., 2017;Setifi et al., 2017). Furthermore, the use of polynitrile anions for the synthesis of interesting discrete and polymeric bistable materials has been described (Setifi et al., 2014;Milin et al., 2016;Pittala et al., 2017). In view of this coordinating ability, these ligands have also been explored for their utility in developing materials capable of magnetic exchange coupling (Addala et al., 2015;Dé niel et al., 2017). It was during the course of attempts to prepare such complexes with 1,10-phenanthroline as a co-ligand that the title complex, (I), was unexpectedly ISSN 2056-9890 obtained. Herein, the crystal and molecular structures of (I) are described, a study complemented by an analysis of the molecular packing by calculating the Hirshfeld surfaces as well as a computational chemistry study.

Structural commentary
The molecule of (I) is shown in Fig. 1 and selected geometric parameters are collated in Table 1. The Co II complex features a chelating 1,10-phenanthroline ligand, a monodentate sulfate di-anion and three coordinated water molecules. The resulting N 2 O 4 donor set defines a distorted octahedral coordination geometry for the Co II atom, with the water molecules occupying one octahedral face. The greatest deviations from a regular geometry is seen in the restricted bite angle subtended by the 1,10-phenanthroline ligand, i.e. N1-Co1-N2 = 78.21 (6) , and in the trans O2W-Co-N2 angle of 166.55 (6) . The Co-N bond lengths are equal within experimental error but the Co-O(aqua) bonds span an experimentally distinct range,  (14) Å for S1-O2, to 1.4813 (14) Å for S1-O3. As discussed below, the sulfate-O1-O4 oxygen atoms form, respectively, one, one, two and two hydrogen bonds with the water molecules, which is consistent with the S1-O2 bond length being the shortest of the four bonds. The above notwithstanding, it is likely that the formal negative charge on the SO 3 residue is delocalized over the three non-coordinating S-O bonds.

Supramolecular features
Each of the aqua ligands donates two hydrogen bonds to different sulfate-O atoms, one of these hydrogen bonds is intramolecular while the remaining are intermolecular, Table 2. The result of the hydrogen bonding is the formation of a supramolecular layer lying parallel to (110). A simplified view of the hydrogen bonding scheme is shown in Fig. 2(a). The aqua molecule forming the intramolecular O1W-HÁ Á ÁO3 hydrogen bond forms a second hydrogen bond to the coordinated O1 atom of a symmetry-related molecule, and the O2W aqua ligand of this molecule connects to the O3 atom of the original molecule, leading to the formation of a nonsymmetric eight-membered {Á Á ÁHOHÁ Á ÁOÁ Á ÁHOCoO} synthon. The second hydrogen atom of the O2W ligand forms a connection to a sulfate-O4 atom, which is also hydrogen bonded to an O3W molecule, which forms an additional link to a symmetry related sulfate-O2 atom with the result a {Á Á ÁHOHÁ Á ÁOSOÁ Á ÁHOHÁ Á ÁO} non-symmetric ten-membered synthon is formed. Two additional eight-membered synthons, {HOCoOHÁ Á ÁOSO}, are formed as a result of the hydrogenbonding scheme as adjacent pairs of aqua molecules effectively bridge two sulfoxide residues. As seen from Fig. 2(  Symmetry codes: (i) Àx þ 1; y À 1 2 ; Àz þ 1 2 ; (ii) Àx þ 1; y þ 1 2 ; Àz þ 1 2 ; (iii) x þ 1; y; z; (iv) x þ 1 2 ; Ày þ 3 2 ; Àz þ 1.

Figure 1
The molecular structure of (I) showing the atom-labelling scheme and displacement ellipsoids at the 50% probability level.  Table 2. A deeper analysis of the molecular packing is found in the next two sections of this paper.

Hirshfeld surface analysis
In order to understand further the interactions operating in the crystal of (I), the Hirshfeld surfaces and two-dimensional fingerprint plots were calculated employing the program Crystal Explorer 17 (Turner et al., 2017) and literature procedures (Tan et al., 2019). The intermolecular O-HÁ Á ÁO hydrogen bonds in (I), Table 2, are characterized as pairs of bright-red spots near the aqua-O and sulfate-O atoms on the Hirshfeld surface mapped over d norm shown in Fig. 3. The faint-red spots near the phenanthroline-C-H (H1, H3 H6 and H10) atoms on the d norm -mapped Hirshfeld surface in the two views of Fig. 4 represent the influence of the weak C3-H3Á Á ÁO2 and C10-H10Á Á ÁO1 interactions as well as H1Á Á ÁO3, H6Á Á ÁO3W short contacts, Table 3. The donors and acceptors of the weak C-HÁ Á ÁO interaction are viewed as blue and red regions on the Hirshfeld surface mapped over the calculated electrostatic potential in Fig. 5, and which correspond to positive and negative electrostatic potentials. The overall two-dimensional fingerprint plot of (I) is shown in Fig. 6(a). The overall contacts are also delineated into HÁ Á ÁH, HÁ Á ÁO/OÁ Á ÁH, HÁ Á ÁC/CÁ Á ÁH and CÁ Á ÁC contacts, as displayed in Fig. 6(b)-(e), respectively. The short interatomic HÁ Á ÁH contacts are characterized as the pair of beak-shaped research communications Acta Cryst. (2020). E76, 835-840 Table 3 A summary of short interatomic contacts (Å ) in (I) a .

Contact
Distance Symmetry operation    Two views of the Hirshfeld surface mapped over d norm for (I) in the range of À0.729 to +1.105 arbitrary units, highlighting weak C-HÁ Á ÁO interactions and short contacts. Fig. 6(b), and contribute 28.6% to the overall surface contacts. The significant O-HÁ Á ÁO contacts between the aqua-and sulfate-O atoms make the major contribution to the overall contacts (44.5%), and these are represented as pairs of well-defined spikes at d e + d i $1.7 Å in Fig. 6(c). The short interatomic HÁ Á ÁC/CÁ Á ÁH (19.5%) and CÁ Á ÁC (5.7%) contacts are, respectively, characterized as pairs of broad symmetrical wings at d e + d i $2.9 Å in Fig. 6(d), and the vase-shaped distribution of points at d e + d i $3.5 Å in Fig. 6(e). The accumulated contribution of the remaining interatomic contacts is less than 2% and has a negligible effect on the packing.

Computational chemistry
In the present analysis, the pairwise interaction energies between the molecules in the crystal were calculated by summing up four different energy components, i.e. the electrostatic (E ele ), polarization (E pol ), dispersion (E dis ) and exchange-repulsion (E rep ) energy terms, after Turner et al.  (Edwards et al., 2017). The intermolecular interaction energies are collated in Table 4. Consistent with the presence of strong O-HÁ Á ÁO hydrogen-bonding interactions in the crystal, the electrostatic energy component has a major influence in the formation of supramolecular architecture of (I), Table 4. The energy associated with the C-HÁ Á ÁO interactions involving the sulfate-O atoms (À66.8 and À55.7 kJ mol À1 ) are greater than for the C-HÁ Á ÁO interaction involving the aqua-O atoms (À30.6 kJ mol À1 ). The energy frameworks were also computed and illustrate the above conclusions, Fig. 7. These clearly demonstrate the dominance of the electrostatic potential energy in the molecular packing.
The key difference in the packing between the two isomers arises as one sulfate-O atom in the mer-isomer participates in three hydrogen bonds at the expense of the hydrogen bond involving the coordinated sulfate-O1 atom. The presence of inter-layer phenanthroline-C-HÁ Á ÁO(sulfate) interactions persist as for the fac-isomer with the crucial difference thatstacking interactions are evident in the inter-layer region of the mer-form with the shortest separation being 3.76 Å .
The different packing arrangements result in different densities with that for (I) of 1.776 g cm À3 being greater than 1.723 g cm À3 for the mer-isomer (FICNOU; Li & Zhou, 1987). The calculated packing efficiencies follow this trend being 72.8 and 66.5%, respectively. Similar results are noted for the pair of Mn structures, i.e. 1.690 g cm À3 and 71.1% for the facisomer (Zheng et al., 2000) c.f. 1.643 g cm À3 and 68.7% for the mer-isomer (Zheng et al., 2000). The consistency of these parameters may suggest that the fac-isomer in these M(1,10phenanthroline)(OH 2 ) 3 OSO 3 complexes is the thermodynamically more stable form.
Given the isostructural relationship in the series (I), IJOQAA, RACWUO and XATNAH, it was thought of interest to compare the percentage contributions of the difference intermolecular contacts to the calculated Hirshfeld surfaces. Thus, these were calculated for the three literature structures as were the overall and delineated two-dimensional fingerprint plots. Qualitatively, the fingerprint plots had the same general appearance in accord with expectation . The calculated percentage contributions to the Hirshfeld surfaces for the four complexes are collated in Table 5. Clearly and as would be expected, the data in Table 5 reveal a high degree of concordance in the percentage contributions to the Hirshfeld surfaces between the four isostructural complexes.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 6. The carbon-bound H atoms were placed in calculated positions (C-H = 0.95 Å ) and were included in the refinement in the riding-model approximation, with U iso (H) set to 1.2U eq (C). The oxygen-bound H atoms were located from a difference-Fourier map and refined with Perspective views of the energy frameworks calculated for (I), showing the (a) electrostatic potential force, (b) dispersion force and (c) total energy, each plotted down the b axis. The radii of the cylinders are proportional to the relative magnitudes of the corresponding energies and were adjusted to the same scale factor of 20 with a cut-off value of 5 kJ mol À1 within 2 Â 2 Â 2 unit cells.   program(s) used to solve structure: SHELXS (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2018/3 (Sheldrick, 2015b); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012), DIAMOND (Brandenburg, 2006); software used to prepare material for publication: publCIF (Westrip, 2010).

fac-Triaqua(1,10-phenanthroline-κ 2 N,N′)(sulfato-κO)cobalt(II)
Crystal data  (Parsons et al., 2013). Absolute structure parameter: 0.0101 (17) 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.