Abstract
The copper coordination chemistry of a new imidazolidine‐based doubly bridging μ‐bis(tetradentate) ligand, H~3~mhbai is studied. A new family of pentacoordinate dinuclear complexes of formula [Cu^II^~2~(‐mhbai)(‐X)]·2 H~2~O (1–4) [X = OAc, NO~3~, Cl, S~2~COMe], where H~3~mhbai stands for 2‐(2‐hydroxyphenyl)‐1,3‐bis[4‐(2‐hydroxyphenyl)‐4‐methyl‐3‐aza‐but‐3‐enyl]‐2‐methyl‐1,3‐imidazolidine, were synthesized from the ligand, H~3~mhbai in air. The complex 1 was structurally characterized by X‐ray crystallography. The μ‐η^1^:η^1^‐N,N'‐imidazolidine bridging mode between two copper(II) ions has been identified in this complex along with a nonhelical binding mode of the μ‐bis(tetradentate) ligand. Variable temperature (2–300 K) magnetic susceptibility data of 1 show the presence of a weak antiferromagnetic exchange interaction between the two triply bridged magnetically isolated copper(II) (S = 1/2) ions. The χ~m~T values start to drop at temperature below 50 K, to reach a value of 0.55 cm^3^ K mol^–1^ at 2 K for a coupling constant value of J = –2.2 cm^–1^. The ^1^H NMR spectrum of the weakly coupled complex 1 shows a total of seventeen hyperfine shifted peaks, as expected from the idealized C~s~ symmetry of the compound, spread over a very large window of chemical shift, spanning about 130 ppm. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)