Crystal structure of bis{3-(3,5-dichlorophenyl)-5-[6-(1 H -pyrazol-1-yl)pyridin-2-yl]-4 H -1,2,4-triazol-4-ido}iron(II) methanol disolvate

The asymmetric unit of the title compound, [Fe II (C 16 H 9 Cl 2 N 6 ) 2 ] (cid:2) 2CH 3 OH, consists of half of a charge-neutral complex molecule and a discrete methanol molecule. The planar anionic tridentate ligand 2-[5-(3,5-dichlorophenyl)-4 H - 1,2,4-triazol-3-ato]-6-(1 H -pyrazol-1-yl)pyridine coordinates to the Fe II ion through the N atoms of the pyrazole, pyridine and triazole groups, forming a coordination


Chemical context
Meridional tridentate ligands, to which different bisazolepyridines belong, are a common choice for the synthesis of Fe II spin-crossover compounds able to switch between a high-spin state (t 2g 4 e g 2 , total spin S = 2) and the low-spin state (t 2g 6 e g 0 , total spin S = 0) due to temperature change, irradiation or external pressure (Goodwin, 2004;Halcrow et al., 2019). In the case of asymmetric ligands with one of the azole groups carrying a hydrogen on the nitrogen heteroatom, deprotonation can produce neutral [Fe(ligand) 2 ] complexes that can be high-spin (Schä fer et al., 2013), low-spin (Shiga et al., 2019) or spin crossover (Seredyuk et al., 2014), depending on the constituent organic groups, solvent molecules and the way that the molecules interact in the lattice (Seredyuk et al., 2022).

Structural commentary
The asymmetric unit comprises half of the molecule and a discrete MeOH molecule forming an O26-H26Á Á ÁN16 hydrogen bond with the triazole (trz) ring and a weak C5-H5Á Á ÁO26 bond with the pyridine (py) ring (Fig. 1). The Fe II ion has a pseudo-octahedral coordination environment composed of the nitrogen donor atoms of the pyrazole (pz), py, and trz heterocycles with an averaged <Fe-N> distance of 1.953 Å (V[FeN 6 ] = 9.610 Å 3 ) that is typical for low-spin complexes with an N 6 coordination environment (Gü tlich & Goodwin, 2004). The pz, py, trz, and phenyl rings of the ligand lie essentially in the same plane (r.m.s.deviation = 0.156 Å ).
The average trigonal distortion parameters AE = AE 1 12 (|90 À ' i |), where ' i is the N-Fe-N 0 angle (Drew et al., 1995), and Â = AE 1 24 (|60 À i |), where i is the angle generated by the superposition of two opposite faces of the octahedron (Chang et al., 1990), are 91.2 and 291.5 , respectively. The values reveal a deviation of the coordination environment from an ideal octahedron in the expected range for complexes with similar bisazolepyridine ligands (see below). The calculated continuous shape measure [CShM(O h )] value relative to the ideal octahedral symmetry is 2. 16 (Kershaw Cook et al., 2015).

Supramolecular features
As a result of their tapered shape, neighbouring complex molecules are embedded in each other and interact through two weak intermolecular C-H(pz)Á Á Á(ph i ) contacts between the pyrazole (pz) and phenyl (ph) groups [the C(12)(pz)Á Á ÁC g (ph i ) distance is 3.458 Å and the angle between the ring planes is 80.0 ; symmetry code: (i) À1 + x, 1 2 À y, 1 2 À z]. The formed one-dimensional supramolecular columns protrude along the a-axis with a stacking periodicity equal to 10.4669 (6) Å (= cell parameter a) (Fig. 2a). As a result of weak intermolecular C-H(pz,py)Á Á ÁN/C(pz,trz)/O(MeOH) hydrogen bonds in the range 2.826 (5)-3.779 (5) Å (Table 1), neighbouring columns are joined into corrugated di-periodic layers in the ac plane (Fig. 2b,c). The layers stack along the baxis direction, forming weak C-H(ph)Á Á ÁCl(ph ii ) [symmetry code: (ii) 2 À x, 1 À y, Àz] interlayer interactions shorter than the sum of the van der Waals radii, two per each phenyl group (Fig. 2c). The voids between the layers are occupied by methanol molecules, which participate in the strong and weak hydrogen bonding mentioned above. A complete list of intermolecular interactions is given in Table 1.

Figure 1
The molecular structure of half of the title compound with displacement ellipsoids drawn at the 50% probability level. The strong O-HÁ Á ÁN and weak C-HÁ Á ÁO/N/C/Cl hydrogen bonds are shown with the nearest neighbours. Symmetry codes: ( Fig. 3a). The pale-red spots indicate short contacts and negative d norm values on the surface correspond to the interactions described above. The overall two-dimensional fingerprint plot is illustrated in Fig. 4. The Hirshfeld surfaces mapped over d norm are shown for the HÁ Á ÁH, HÁ Á ÁC/CÁ Á ÁH, HÁ Á ÁCl/ClÁ Á ÁH and HÁ Á ÁN/NÁ Á ÁH contacts, and the twodimensional fingerprint plots, associated with their relative contributions to the Hirshfeld surface. At 26.1%, the largest contribution to the overall crystal packing is from HÁ Á ÁH interactions, which are located mostly in the middle region of the fingerprint plot. HÁ Á ÁC/CÁ Á ÁH contacts contribute 24.4% and HÁ Á ÁCl/ClÁ Á ÁH 18.9%, resulting in a pair of characteristic wings. The HÁ Á ÁN/NÁ Á ÁH contacts, represented by a pair of sharp spikes in the fingerprint plot, make a 12.1% contribution to the Hirshfeld surface. The electrostatic potential energy calculated using the B3LYP/6-31G(d,p) basis set localizes the negative charge on the trz-ph moieties of the complex molecule, while the pz-py moieties are relatively positively charged (Fig. 3b). The polar nature of the molecule justifies the realized stacking in columns.

Energy framework analysis
The energy framework (Spackman et al., 2021) with total energy values (E tot ) calculated using the wavefunction at the B3LYP/6-31G(d,p) theory level are shown in Fig. 5a. The cylindrical radii are proportional to the relative strength of the corresponding energies. The major contribution to the intermolecular interactions comes from dispersion forces (E dis ), reflecting the dominant type of interactions in the network of the electroneutral molecules (see the table in Fig. 5). The energy framework topology reproduces the topology of intermolecular interactions within and between supramolecular layers, including the electron-density distribution within the molecule analysed above using mapped Hirshfeld surfaces.    within the supramolecular columns and between the columns within the layers correspond to interaction energies of À48.6 and À67.9 kJ mol À1 , respectively (Fig. 5b). As for the interlayer interactions, the double supramolecular C-HÁ Á ÁCl ii [symmetry code: (ii) 2 À x, 1 À y, Àz] bonding between neighbouring phenyl rings leads to an interaction energy of À5.6 kJ mol À1 , while the stacking of the moieties corresponds to an interaction energy of À21.7 kJ mol À1 (Fig. 5c) (Gentili et al., 2015;Senthil Kumar et al., 2015). The Fe-N distances for these complexes in the lowspin state are close to the value in the title compound, while in the high-spin state it is larger by $0.2 Å . The trigonal distortion indices change correspondingly, and in the low-spin state they are systematically lower than in the high-spin state. Table 2 collates the structural parameters of the complexes and of the title compound.

Refinement details
Crystal data, data collection and structure refinement details are summarized in Table 3. H atoms were placed in calculated positions using idealized geometries, with C-H = 0.98 Å for methyl groups and 0.95 Å for aromatic H atoms, and refined using a riding model with U iso (H) = 1.2-1.5U eq (C); the hydrogen atom H26 was refined freely.  (Rigaku OD, 2022); cell refinement: CrysAlis PRO (Rigaku OD, 2022); data reduction: CrysAlis PRO (Rigaku OD, 2022); program(s) used to refine structure: SHELXL2018/3 (Sheldrick, 2015); molecular graphics: Olex2 (Dolomanov et al., 2009); software used to prepare material for publication: Olex2 (Dolomanov et al., 2009). 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.