Preparation of a flexible binucleating ligand, xylylene-bridged biscyclam α,α′-bis(1,4,8,11-tetraazacyclotetradecan-6-yl)-p-xylene and structure of its dinickel(II) complex

A binucleating ligand, xylylene-bridged biscyclam α,α′-bis(1,4,8,11-tetraazacyclotetradecan-6-yl)-p-xylene ((cyclam)₂-p-xyl) was prepared from α,α′-dichloro-p-xylene, diethylmalonate and 1,4,8,11-tetraazaundecane in three steps. The second step, aminolytic condensation of the tetraamine was critical. The ligand yielded a dinickel(II) complex (Ni₂(cyclam)₂-p-xyl](ClO₄)₄ · 4H₂O. X-ray crystal analysis of the complex disclosed opposite and almost perpendicular occupation of the macrocycles to the bridging benzene ring through equatorial connection at the 6-carbons. Crystal data: tetragonal space group P4₂, a = 15.251(2), c = 9.821(2) A ̊ V = 2284.3(6) A ̊³ Z = 2. It is anticipated that conformational change in solution due to free rotation around the methylene carbon at the junction puts the macrocycles into face-to-face location with NiNi distance of ∼ 7.7 Å.