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

The title charge-neutral complex shows a cis-arrangement of the thiocyanate anions, with a severely distorted coordination polyhedron. The one-dimensional supramolecular architecture of the lattice is formed by weak C⋯C/S/N interactions and weak C—H⋯O/C/S/N hydrogen bonds.


Chemical context
Fe II complexes based on Schiff bases derived from N-substituted 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 all of the charge-neutral mononuclear complexes of this kind described so far, the thiocyanate anions occupy the axial position in 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 the four N atoms of the tetradentate Schiff-base ligand and the two NCS À counter-ions (Fig. 1). The average bond length, <Fe-N> = 2.167 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 91.6 (1) . The average trigonal distortion parameters, AE = AE 1 12 (|90 À ' i |), where ' i is the angle N-Fe-N 0 (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 an octahedron (Chang et al., 1990), are 127.4 and 481.9 , respectively. The 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 measurements (CShM), the shape closest to the Fe-based coordination polyhedron and its distortion can be determined numerically (Kershaw Cook et al., 2015). The calculated CShM value relative to ideal O h symmetry is 4.269, and 5.671 relative to ideal D 3h trigonal-prismatic symmetry. Hence, the coordination polyhedron is closer to the former geometry, but is appreciably distorted, as indicated by the calculated value (for an ideal polyhedron CShM = 0). The volume of the [FeN 6 ] coordination polyhedron is 12.50 Å 3 .

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. Weak intermolecular elementÁ Á Áelement contacts are represented by dashed red lines.

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., 2017), with a standard resolution of the three-dimensional d norm surfaces plotted over a fixed colour scale of À0.3171 (red) to 1.6637 (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 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 37.5%, 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 24.7%, and the HÁ Á ÁS/SÁ Á ÁH contacts contribute 15.7% 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 11.7% contribution to the Hirshfeld surface.

Magnetic properties
Variable-temperature magnetic susceptibility measurements were performed on single crystals (10 mg) of the title compound using a Quantum Design MPMS2 superconducting quantum interference device (SQUID) susceptometer operating at 1 T in the temperature range 10-400 K. Experimental susceptibilities were corrected for the diamagnetism of the holder (gelatine capsule) and of the constituent atoms by the   Two projections of d norm mapped on Hirshfeld surfaces, showing the interactions between molecules. Red areas represent regions where contacts are shorter than the sum of the van der Waals radii, blue areas represent regions where contacts are larger than the sum of van der Waals radii, and white areas are regions where contacts are close to the sum of van der Waals radii. application of Pascal's constants. The magnetic behaviour of the compound is shown in Fig. 5 in the form of M T versus T ( M is the molar magnetic susceptibility and T is the temperature). At 300 K, the M T value is close to 3.40 cm 3 K mol À1 , and on cooling the value remains constant down to 30 K. The decrease in M T below 30 K is attributed to the zero-field splitting of the high-spin (S = 2) Fe II centres (Kahn, 1993), which corroborates well with the observed long average Fe-N bond length and the large geometric distortion of the coordination polyhedron of the central Fe II ion.

Database survey
A search of the Cambridge Structural Database (CSD, online) reveals five similar Fe II thiocyanate complexes: derivatives of 1,3-diamine and N-substituted 1,2,3-triazole aldehydes: DURXEV, ADAQUU, ADAREF and solvatomorphs ADAROP and ADARUV Hagiwara & Okada, 2016). These complexes show hysteretic spin crossover with variation of 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 highspin state of the Fe II ions. The reported pseudo-trigonalprismatic complexes with an [FeN 6 ] chromophore are formed by structurally hindered rigid hexadentate ligands favouring a trigonal geometry of the central Fe II ion: CABLOH (Voloshin et al., 2001), BUNSAF (El Hajj et al., 2009), OWIHAE (Seredyuk et al., 2011), OTANOO (Stock et al., 2016). The complex CUWQAP, recently reported by us (Znovjyak et al., 2020), has a similar strongly distorted coordination environment of the central Fe II ion. Table 2 collates the distortion parameters AE, Â and CShM for the pseudo-trigonal-prismatic complexes mentioned above.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3     etrically (C-H = 0.93-0.97 Å ) and refined as riding with U iso (H) = 1.2U eq (C) or 1.5U eq (C-methyl).