Structural and Spectral Studies on the Ni(II) Complexes of 1,5-Diazacyclooctane (DACO) Bearing Heterocyclic Pendants: Formation of a Two-dimensional Network via Hydrogen Bonds and π-π Stacking Interactions

A penta-coordinated Ni(II) complex with a 1,5-diazacyclooctane (DACO) ligand functionalized by two imidazole donor pendants, [NiL¹Cl] (ClO₄) H₂O (1) (where L¹ = 1,5-bis (imidazol-4-ylmethyl)-l,5-diazacyclooctane) has been synthesized and characterized by X-ray diffraction, infrared spectra, elemental analyses, conductance, thermal analyses and UV-Vis techniques. Complex 1 crystallizes in triclinic crystal system, P-l space group with a = 0.74782(7), b = 1.15082 (10), c = 1.23781(11) nm, α = 82.090(2), β = 73.011(2), γ = 83.462(2)°, V = 1.00603(16) nm³, M, = 486.00, Z = 2, D_c = 1.604 g/cm³, final R = 0.0435, and wR = 0.1244. The structures of 1 and its related complexes show that in all the three mononuclear complexes, each Ni(II) center is penta-coordinated with a near regular square pyramid (RSP) to distorted square-pyramidal (DSP) coordination environment due to the boat/chair configuration of DACO ring in these complexes, and the degree of distortion increases with the augment of the size of the heterocyclic pendants. In addition, the most striking feature of complex 1 resides in the formation of a two-dimensional network structure through hydrogen bonds and stabilized by π-π stacking. The solution behaviors of the Ni(II) complexes are also discussed in detail.