Bimetallic copper complexes of a new amide-based heptadentate N6O ligand: Design, syntheses, structures, and spectroscopic characterization

A new dicompartmental N₆O heptadentate ligand has been prepared by linking two bis(pyrazolyl)methane donor groups to a phenol core via amide bridges attached to the 2 and 6 positions of the arene ring. The ligand Bu^t-Ph(OH)–[NH–C(O)–CH(pz)₂]₂ (H₃L, pz = pyrazolyl ring) forms the neutral complexes {Bu^t-Ph(O)–[N–C(O)–CH(pz)₂]₂}[Cu₂(μ-O₂C–CH₃)] (1), and {Bu^t-Ph(O)-[N–C(O)–CH(pz)₂]₂}{Cu₂[μ-O₂C–CH(NI)–CH(CH₃)(CH₂CH₃)]} (2, NI = 1,8-Naphthalimide). These compounds were characterized by ¹H NMR, IR, and UV–Vis spectroscopies, as well as single crystal X-ray diffraction. Their common structural features consist of a triply deprotonated [L]^3- ligand, bridging two copper(II) ions through the phenoxido oxygen atom. The neutrality of the complexes is ensured by the exogenous C(O)O⁻ bridges. As a consequence, the distances between the Cu²⁺ ··· Cu²⁺ ions were found to be about 3.5 Å in both cases. Each copper center is also coordinated by three nitrogen atoms, originating from the deprotonated amide group and the two pyrazolyl rings of the side-arms of the ligand. As such, the geometry around the copper ions can be described as a distorted square pyramid.