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

The title compound, a charge-neutral bis{2-(3,4-dimethylphenyl)-4H-1,2,4-triazol-3-ato)-6-(1H-πyrazol-1-yl)pyridine} iron(II) complex dimethanol solvate, is a low-spin complex with a moderately distorted pseudooctahedral coordination environment of the metal ion. As a result of the cone shape, the molecules are stacked in mono-periodic columns that are bound by weak hydrogen bonds into di-periodic layers, which, in turn, are arranged in a three-dimensional lattice bound by weak interlayer interactions.


Chemical context
Bisazolepyridines are a broad class of meridional tridentate ligands used to synthesize charged Fe II compounds capable of switching between a spin state with the t 2g 4 e g 2 configuration (high-spin, total spin S = 2) and a spin state with the t 2g 6 e g 0 configuration (low-spin, total spin S = 0) due to temperature variation, light irradiation or external pressure (Halcrow, 2014;Halcrow et al., 2019). In the case of asymmetric ligand design, where one of the azole groups carries a hydrogen on the nitrogen heteroatom, it was shown that deprotonation can produce neutral complex species that can be high-spin (Schä fer et al., 2013), low-spin (Shiga et al., 2019) or exhibit temperature-induced transitions between the spin states of the central atom (Seredyuk et al., 2014), depending on the ligand field strength. The substituents of ligands can also play an important role in behaviour of the solid samples, determining the way molecules interact with each other and, therefore, influencing the spin state adopted by the central atom. As we have recently shown, the dynamic rearrangement of the substituent groups can lead to an abnormally large hysteresis of the thermal high-spin transition due to the supramolecular mechanism of blocking the deformation of the complex molecule by the methoxy group (Seredyuk et al., 2022).

Structural commentary
The asymmetric unit comprises half of the molecule and a discrete MeOH molecule forming a hydrogen bond O26-H26Á Á ÁN12 with the triazole (trz) ring (Fig. 1). The Fe II ion has a pseudo-octahedral coordination environment composed of the nitrogen donor atoms of the pyrazole (pz), pyridine (py) and trz heterocycles with an average Fe-N distance of 1.957 Å (V[FeN 6 ] = 9.654 Å 3 ) being typical for low-spin complexes with an N 6 coordination environment (Gü tlich & Goodwin, 2004). The pz, py, trz and phenyl rings, together with the two methyl substituents of one ligand, all lie essentially in the same plane.
The average trigonal distortion parameters, AE = AE 1 12 (|90 À ' i |), with ' i being the N-Fe-N 0 angle (Drew et al., 1995), and Â = AE 1 24 (|60 À i |), with i being the angle generated by superposition of two opposite faces of the octahedron (Chang et al., 1990), are 92.8 and 295.0 , respectively. The values reveal a deviation of the coordination environment from an ideal octahedron which is, however, in the expected range for complexes with similar bisazolepyridine ligands (see below). The calculated continuous shape measure (CShM) value relative to the ideal O h symmetry is 2.18 (Kershaw Cook et al., 2015).

Supramolecular features
As a result of the tapered shape, neighbouring complex molecules are embedded in each other and interact through two weak intermolecular C-H(pz)Á Á Á(ph') contacts between the pyrazole (pz) and phenyl (ph) groups, respectively [distance C2)(pz)Á Á ÁC g (ph') is 3.392 Å , angle between planes of the rings is 73.77 ]. The formed mono-periodic supramolecular columns protrude along the c-axis with a stacking periodicity equal to 10.6511 (7) Å (= cell parameter c) (Fig. 2a)    The molecular structure of half the title compound as refined in the asymmetric unit with displacement ellipsoids drawn at the 50% probability level. The O-HÁ Á ÁN hydrogen bond is indicated by the dashed line. This and the next figure were generated with the program Mercury (Macrae et al., 2020). Table 1 Hydrogen bonding (Å ) of the title compound.

Hirshfeld surface and 2D fingerprint plots
Hirshfeld surface analysis was performed and the associated two-dimensional fingerprint plots were generated using Crystal Explorer (Spackman et al., 2021), with a standard resolution of the three-dimensional d norm surfaces plotted over a fixed colour scale of À0.6122 (red) to 1.3609 (blue) a.u. (Fig. 3). The pale-red spots symbolize 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 ÁN/NÁ Á ÁH and CÁ Á ÁC contacts, and the two-dimensional fingerprint plots, associated with their relative contributions to the Hirshfeld surface. At 48.5%, the largest contribution to the overall crystal packing is from HÁ Á ÁH interactions, which are located mostly in the central region of the fingerprint plot. HÁ Á ÁC/CÁ Á ÁH contacts contribute 28.9%, 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 16.2%   contribution to the Hirshfeld surface. Finally, CÁ Á ÁC contacts, which account for a contribution of 2.4%, are mostly distributed in the middle part of the plot.

Energy frameworks
The energy frameworks, calculated using the wave function at the B3LYP/6-31G(d,p) theory level, including the electrostatic potential forces (E ele ), the dispersion forces (E dis ) and the total energy diagrams (E tot ), are shown in Fig. 5 (Spackman et al., 2021). The cylindrical radii, adjusted to the same scale factor of 100, 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 interactions in the network of the electroneutral molecules. The topology of the energy framework resembles the topology of the intermolecular interactions within and between the supramolecular layers described above. Because of the high lattice symmetry, there are only two different attractive interactions between the molecules within the layers, equal to À58.5 and À90.6 kJ mol À1 . As for the interlayer interactions, the absence of supramolecular bonding leads to very weak interactions in the range À7.4 to +2.5 kJ mol À1 , i.e. from weakly attracting to weakly repulsive. The colour-coded interaction mappings within a radius of 3.     Table 2.

Refinement
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. Two OMIT commands were used to exclude beamstop-affected data.

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