Crystal structure of {N 1,N 3-bis[(1-benzyl-1H-1,2,3-triazol-4-yl)methylidene]-2,2-dimethylpropane-1,3-diamine}bis(thiocyanato-κN)iron(II)

The title compound shows a cis-arrangement of the thiocyanate anions, while the coordination polyhedron around the iron(II) atom is close to a trigonal prism.

Iron(II) complexes based on Schiff bases derived from Nsubstituted 1,2,3-triazole aldehydes represent an interesting class of coordination compounds exhibiting spin-state switching between low-and high-spin states in different temperature regions (Hagiwara et al., 2014(Hagiwara et al., , 2020Hora & Hagiwara, 2017). In charge-neutral mononuclear complexes of this kind described so far, the thiocyanate anions occupy the axial position of the coordination sphere and thus are in a trans-configuration (Hagiwara & Okada, 2016;Hagiwara et al., 2017).

Structural commentary
The Fe II ion of the title complex has a distorted trigonalprismatic N 6 coordination environment formed by four N atoms of the tetradentate Schiff-base ligand and two NCS À counter-ions (Fig. 1). The average bond length <Fe-N> = 2.19 (9) Å is typical for high-spin complexes with an [FeN 6 ] chromophore (Gü tlich & Goodwin, 2004). The N-Fe-N angle between the cis-aligned thiocyanate N atoms is 87.58 (9) . The average trigonal distortion parameters et al., 1995), and Â = AE 1 24 (|60 À i |), where i is the angle generated by superposition of two opposite faces of an octahedron (Chang et al., 1990), are 453.2 and 149.38 , respectively. These values reveal a great deviation of the coordination environment from an ideal octahedron (where AE = Â = 0), and are significantly larger than those of similar [FeN 6 ] high-spin trans-complexes . With the aid of continuous shape measure (CShM), the closest shape of a coordination polyhedron and its distortion can be determined numerically (Kershaw Cook et al., 2015). The calculated CShM value relative to the ideal O h symmetry for an octahedron is 6.285, while it is 4.008 relative to the ideal D 3h symmetry for a trigonal prism. Hence, the polyhedron is closer to the latter shape; however, it is notably distorted (for the ideal polyhedron CShM = 0). The volume of the [FeN 6 ] coordination polyhedron is 12.4 Å 3 .

Figure 2
Weak hydrogen bonding (cyan dashed lines), resulting in the formation of chains in the packing.

Figure 1
The molecular structure of the title compound with displacement ellipsoids drawn at the 50% probability level. H atoms have been omitted for clarity. bouring complex molecules, forming a two-dimensional supramolecular array extending parallel to (011).

Hirshfeld surface and 2D fingerprint plots
Hirshfeld surface analysis was performed and the associated two-dimensional fingerprint plots were generated using Crystal Explorer (Turner et al., 2018), with a standard resolution of the three-dimensional d norm surfaces plotted over a fixed colour scale of À0.2801 (red) to 1.8236 (blue) a.u. 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. 3. The Hirshfeld surfaces mapped over d norm are shown for the HÁ Á ÁH, HÁ Á ÁC/CÁ Á ÁH, HÁ Á ÁS/SÁ Á ÁH, and HÁ Á ÁN/ NÁ Á ÁH contacts, and the two-dimensional fingerprint plots are presented in Fig. 4, associated with their relative contributions to the Hirshfeld surface. At 35.2%, the largest contribution to the overall crystal packing is from HÁ Á ÁH interactions, which are located in the middle region of the fingerprint plot. HÁ Á ÁC/ CÁ Á ÁH contacts contribute 26.4%, and the HÁ Á ÁS/SÁ Á ÁH contacts contribute 19.3% to the Hirshfeld surface, both 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 13.9% contribution to the Hirshfeld surface.

Database survey
A search of the Cambridge Structural Database (CSD 2020, update of May 2020; Groom et al., 2016) revealed four similar Fe II thiocyanate complexes, derivatives of a 1,3-diaminopropanes and N-substituted 1,2,3-triazole aldehydes, viz. DURXEV, ADAQUU, ADAREF and solvatomorphs ADAROP and ADARUV Hagiwara & Okada, 2016). These complexes show hysteretic spin crossover with the Fe-N distances in the range 1.931-1.959 Å for the low-spin state and 2.154-2.169 Å for the high-spin state of the Fe II ions. The reported pseudo-trigonal-prismatic complexes with an [FeN 6 ] chromophore are formed by structurally hindered rigid hexadentate ligands favoring a trigonal-prismatic environment of the central Fe II ion in the low-or highspin state: CABLOH (Voloshin et al., 2001), BUNSAF (El Hajj et al., 2009), OWIHAE (Seredyuk et al., 2011), OTANOO (Stock et al., 2016). For comparison purposes, Table 2 collates the distortion parameters AE, Â and CShM for the latter complexes.   Two projections of d norm mapped on Hirshfeld surfaces, showing the intermolecular interactions within the molecule. Red areas represent contacts shorter than the sum of the van der Waals radii, while blue areas represent regions where contacts are larger than the sum of van der Waals radii, and white areas are zones close to the sum of van der Waals radii.

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 = 0.96-0.97 Å for methylene and methyl groups and 0.93 Å for aromatic H atoms, and refined using a riding model with U iso (H) = 1.2-1.5U eq (C).

Funding information
Funding for this research was provided by: H2020 Marie Skłodowska-Curie Actions (grant No. 734322).

κN)iron(II)
Crystal data where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.62 e Å −3 Δρ min = −0.59 e Å −3 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