A comparative study of the packing of two polymorphs of the nickel(II) pincer complex [2,6-bis(di-tert-butylphosphinoyl)-4-(3,5-dinitrobenzoyloxy)phenyl-κ³P,C¹,P′]chloridonickel(II)

Abstract

Pincer complexes can act as catalysts in organic transformations and have potential applications in materials, medicine and biology. They exhibit robust structures and high thermal stability attributed to the tridentate coordination of the pincer ligands and the strong σ metal-carbon bond. Nickel derivatives of these ligands have shown high catalytic activities in cross-coupling reactions and other industrially relevant transformations. This work reports the crystal structures of two polymorphs of the title Ni(II) POCOP pincer complex, [Ni(C29H41N2O8P2)Cl] or [NiCl{C6H2-4-[OCOC6H4-3,5-(NO2)2]-2,6-(OP(t)Bu2)2}]. Both pincer structures exhibit the Ni(II) atom in a distorted square-planar coordination geometry with the POCOP pincer ligand coordinated in a typical tridentate manner via the two P atoms and one arene C atom via a C-Ni σ bond, giving rise to two five-membered chelate rings. The coordination sphere of the Ni(II) centre is completed by a chloride ligand. The asymmetric units of both polymorphs consist of one molecule of the pincer complex. In the first polymorph, the arene rings are nearly coplanar, with a dihedral angle between the mean planes of 27.9 (1)°, while in the second polymorph, this angle is 82.64 (1)°, which shows that the arene rings are almost perpendicular to one another. The supramolecular structure is directed by the presence of weak C-H...O=X (X = C or N) interactions, forming two- and three-dimensional chain arrangements.