Synthesis and X-ray Structure Combined with Hirshfeld and AIM Studies on a New Trinuclear Zn(II)-Azido Complex with s-Triazine Pincer Ligand

The trinuclear [Zn-3(PMT)(2)(Cl-4)(N-3)(2)] complex of the N-pincer ligand, 2,4-bis(3,5-dimethyl-1H-pyrazol-1-yl)-6-methoxy-1,3,5-triazine (PMT), was obtained by self-assembly of the polydentate ligand (PMT) with ZnCl2 in the presence of azide ion as an auxiliary bridging ligand. The X-ray structure analysis revealed a monoclinic crystal system and centrosymmetric space group C2/c. There are two crystallographically independent Zn(II) sites where the Zn1 and Zn2 are tetra- and penta-coordinated with ZnN2Cl2 and ZnN4Cl coordination environments, respectively. The distortion tau(4) and tau(5) parameters for the Zn1 and Zn2 sites are 0.93 and 0.52, respectively. Hence, the Zn(1)N2Cl2 has a distorted tetrahedral configuration, while the Zn(2)N4Cl coordination sphere is intermediate between the square pyramidal and trigonal bipyramidal configurations. In this complex, the PMT is a tridentate N-chelate, while the chloride and azide anions are terminal and mu(1,1) bridged ligands, respectively. The %H horizontal ellipsis H, N horizontal ellipsis H, Cl horizontal ellipsis H, and C horizontal ellipsis H are 40.8, 17.2, 16.0, and 10.1%, respectively, based on Hirshfeld analysis. The charges at the Zn1 (+0.996 e) and Zn2 (+1.067 e) sites are calculated to be less than the official charge of the isolated Zn(II) ion. The mu(1,1) bridged azide has two asymmetric N-N bonds with clear covalent characters. In contrast, the Zn-N and Zn-Cl bonds have predominant closed-shell characters.