Synthesis and crystal structure of bis(tert-butyl isocyanide-κC)[5,10,15,20-tetrakis(4-chlorophenyl)porphyrinato-κ4 N]iron(II)

Molecules of the title complex are centrosymmetric and the Fe—N bond lengths to the N atoms of the porphyrin ring indicate that the FeII atom is in the low-spin state.

In the case of the related iron(III) ion complex [Fe III (TPP)(t-BuCN) 2 ] + , these angles exhibit significantly higher values, measuring 174.2 and 173.5 � for the average Fe-C-N and C-N-C angles, respectively.The deviations from linearity, represented by the angles 14.3/16.3� for complex I and 11.0/20.9� for [Fe II (TPP)(t-BuNC) 2 ] (Jameson & Ibers, 1979), are notably greater than those observed in the iron(III) TPP-bis(t-BuNC) derivative, where the average deviation values are 5.8/6.5 � (Walker et al., 1996).The greater deviation from linearity observed in the t-BuCN ligand of ferrous meso-metalloporphyrins, compared to the ferric mesoporphyrin ion complex [Fe III (TPP)(t-BuCN) 2 ] + , is consistent with the dominance of the �-backbonding effect in iron(II) derivatives over iron(III) coordination compounds.
It is certainly true that the iron(II) derivatives display longer C-N distances.Nevertheless, the difference between the longest C-N bond length of an iron(II)-bis(t-BuNC) derivative and the shortest C-N bond length of an iron(III)bis(t-BuNC) metalloporphyrin is small (0.042A ˚).

Supramolecular features
Within the crystal structure of I (Figs. 2 and 3, Table 1), the [Fe II (TClPP)(t-BuNC) 2 ] complexes are linked to each other via weak non-classical C-H� � �Cl, C-H� � �N hydrogen bonds and C-H� � �Cg intermolecular interactions where Cg is the centroid of a pyrrole ring.It may be noted that Cl1 acts as acceptor for three different C-H groups.

FT-IR and UV/Vis spectroscopies
The FT-IR spectrum of [Fe II (TClPP)(t-Bu-NC) 2 ] (I) (Fig. 4) was obtained in the 4000-400 cm À 1 range by a PerkinElmer Spectrum Two FTIR spectrometer.The spectrum exhibits characteristic IR bands of the TClPP porphyrinate.The C-H stretching frequencies of the porphyrin are shown between 3083 and 2923 cm À 1 while �(CH) of the methyl groups of the t-BuNC axial ligand occurs at 2883 cm À 1 .The strong band at 996 cm À 1 is attributed to the bonding vibration �(CCH) of the porphyrin core for which a value around 1000 cm À 1 is characteristic of a metalled porphyrin while a �(CCH) value around 960 cm À 1 is specific of a free base porphyrin.
It has been found that the values of the C N stretching frequency for ferric t-BuNC metalloporphyrins are displaced by at least 60 cm À 1 to higher frequency compared to those of ferrous t-BuNC porphyrin complexes.Thus for the Figure 4 FT-IR spectrum of I.
The UV/Vis spectrum of complex I was obtained in chloroform using a WinASPECT PLUS scanning spectrophotometer (Fig. 5).The measurements were conducted in 1.0 cm path length cuvettes containing dry degassed chloroform solutions, all under an argon atmosphere.The � max value of the Soret band for complex I is 436 nm (Gouterman et al., 1963), which closely resembles the values observed in the related species [Fe II (TPP)(t-BuNC) 2 ] and [Fe II (TBPPP)(t-BuNC) 2 ], which are 432 nm and 437 nm, respectively (Jameson & Ibers, 1979;Nasri et al., 2017).Notably for the bis(t-BuNC) ferric metalloporphyrins, the � max of the Soret band value is blue shifted compared to those of the ferrous bis(t-BuNC) porphyrin complexes, e.g., for [Fe III (TPP)(t-BuNC) 2 ] + (Simonneaux et al., 1989), the � max of the Soret band is 420 nm.

Hirshfeld surface analysis
The supramolecular interactions in the title structure have been further investigated and visualized by Hirshfeld surface (HS) analysis performed with Crystal Explorer 17 (Turner et al., 2017).The Hirshfeld surface of complex I mapped over d norm in the range À 0.19 to 1.14 a.u. is represented in Fig. 6.This study confirms that the crystal packing of complex I is mainly made by C-H� � �Cl, C-H� � �N and C-H� � �Cg intermolecular interactions, as already shown by the PLATON program (Spek, 2020) (Fig. 3).According to the two-dimensional fingerprint plots of complex I shown in Fig. 7, most important intermolecular interactions are H � � �H contacts (61.4%).The C� � �H/H� � �C, O� � �H/H� � �O and N� � �H/H� � �N interactions comprise 21.3%, 13.3% and 3.6% of the HS, respectively.

Special details
Experimental.SADABS-2012/1 (Bruker,2012) was used for absorption correction.wR2(int) was 0.0545 before and 0.0502 after correction.The Ratio of minimum to maximum transmission is 0.9200.The λ/2 correction factor is 0.0015.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 )
Figure2A portion of the crystal packing of the title complex, viewed down [100].

Figure 3 A
Figure 3 A partial view of the crystal packing of I showing the link between the complexes via C __ H� � �Cl and C __ H� � �N hydrogen bonds and by C-H� � �� interactions.

Figure 5
Figure 5UV/Vis spectrum of I recorded in chloroform.

Figure 7
Figure 7 Two-dimensional fingerprint plots of complex I showing close contacts of (a) all contributions in the crystal and those delineated into (b) H� � �H, (c) C� � �H/H� � �C and (d) Cl� � �H/H� � �Cl interactions.

Table 2
Experimental details.