Synthesis, spectroscopic analysis and crystal structure of (N-{2-[(2-aminoethyl)amino]ethyl}-4′-methyl-[1,1′-biphenyl]-4-sulfonamidato)tricarbonylrhenium(I)

The title complex possesses pseudo-octahedral geometry where one face of the octahedron is occupied by three carbonyl ligands and the other face is occupied by one sp2 nitrogen atom of the sulfonamide group and two sp3 nitrogen atoms of the dien backbone.


Chemical context
Organometallic compounds have garnered significant interest due to their notable properties in cell imaging and anticancer applications.Particularly, Re complexes are noted for their kinetic inertness and large Stokes shift (Stephenson et al., 2004;Guo et al., 1997).Research has shown that tridentate ligand systems are more robust and possess better pharmacokinetics than those bearing bidentate ligands, leading to reduced side effects (Schibli et al., 2000).Our focus involves a sulfonamide ligand, which has a diethylenetriamine (dien) backbone and 4-methylbiphenyl (4-Mebip) as the pendant group.The N(SO 2 )(4-Mebip)dienH ligand, along with its bidentate Pt II complex have both been reported to exhibit remarkable anticancer properties against non-small lung cancer (Kaluthanthiri et al., 2023).Motivated by its potential as a cytotoxic drug lead, here we have focused on rhenium, in its lowest oxidation state because it exhibits less reactivity toward species in the cellular environment (Schibli & Schubiger, 2002).Given rhenium's soft metal center characteristics, a preference for soft donors, particularly nitrogen, is observed and tridentate metal complexes featuring nitrogen donors are commonly employed (Christoforou et al., 2007;Kaushalya et al., 2022;Darshani et al., 2020).In this study, the Re(CO) 3 [N(SO 2 )(4-Mebip)dien] complex was successfully synthesized and its molecular structure was confirmed by single-crystal X-ray diffraction analysis and 1 H NMR spectroscopy.Furthermore, comprehensive characterization was conducted using FTIR, UV-vis, and fluorescence spectroscopic techniques.

Structural commentary
The Re(CO) 3 [N(SO 2 )(4-Mebip)dien] complex is shown in Fig. 1.The Re-C distances in Re-CO bonds are in the range of 1.895 (8)-1.914(6) A ˚, which is consistent with related data reported (Christoforou et al., 2007;Darshani et al., 2020).The longest Re-C distance is trans to the sp 2 nitrogen atom N3.The C11-C14 bond distance between the two phenyl rings of the anionic ligand in the biphenyl group in Re(CO) 3 [N(SO 2 )(4-Mebip)dien] is 1.484 (8) A ˚.The biphenyl moiety is twisted out of planarity, the dihedral angle between the two planes being 36.5 (3) � .The average Re-N bond length in our Re complex is 2.206 A ˚, which is consistent with the distances found in related Re(CO) 3 complexes containing a dien backbone (Christoforou et al., 2007).The Re-N3 bond (sp 2 nitrogen) distance [2.173 (4) A ˚] in the complex is significantly shorter than the other Re-N (sp 3 N) bonds [2.217 (5) and 2.228 (6) A ˚], which explains the anionic nature of the N3 amino nitrogen.The S-N bond length for the deprotonated sulfonamido group is 1.579 (4) A ˚for the complex and is within the accepted range for S-N bonds available in deprotonated sulfonamides coordinated to Re, Cu and Zn metals (Christoforou et al., 2007;Goodwin et al., 2004;Congreve et al., 2003).

Supramolecular features
The unit cell is shown in Fig. 2. The intermolecular interactions are predominantly N-H� � �O hydrogen bonds as listed in Table 1 and shown in Fig. 3.The N1� � �O2 separations in these hydrogen bonds are in the range 2.941 (5)-3.053(7) A ˚.The graph sets (Etter et al., 1990) are centrosymmetric R 2 2 (10) rings and C 1 1 (6) chains, forming double-stranded chains in the [001] direction.One of the NH 2 H atoms is not involved in the hydrogen bonding.Interleaved between the double-stranded hydrogen-bonded chains are hydrophobic layers of stacked The asymmetric unit with 50% probability displacement ellipsoids and atom labels.H atoms are represented by spheres of arbitrary radius.

Figure 3
View of the hydrogen bonding, shown as blue dashed lines, and chain formation along the [001] direction.H atoms on C are omitted and the unit cell axes are shown.
biphenyl moieties, as can be seen in Fig. 2. The closest distance [4.079 (4) A ˚] between centers of gravity (Cg) of these rings is between the phenyl ring C14-C19 carrying the methyl group and its centrosymmetric equivalent at 1 À x, 2 À y, 2 À z.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2.All H atoms were located in difference maps and treated as riding in geometrically idealized positions with C-H distances of 0.94 A ˚and with U iso (H) = 1.2U eq for the attached C atom (0.97 A ˚and 1.5U eq for the methyl group).The H atoms on nitrogen had N-H distances of 0.89 A ˚for NH 2 and 0.98 A ˚for NH, and U iso values were assigned as 1.2U eq for the N atom.

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.

Figure 2
Figure 2View of the unit cell.H atoms are not shown.

Table 2
Experimental details.