Binuclear metallacyclic copper(II) complexes with a large unoccupied cavity derived from a tetradentate, nonmacrocyclic polyhydroimidazole ligand

The potentially tetradentate ligand 1,2,4,5-tetrakis(4,5-dihydroimidazol-2-yl)benzene (BTIM) forms bischelating binuclear square-pyramidal copper(II) complexes in which two ligands and two metals form a metallacyclic structure with a very large, unoccupied cavity. The cavity is defined by a large copper-copper separation (Cu-Cu=7.610 A in [Cu 2 (BTIM) 2 Cl 2 ]Cl 2 •7H 2 O (I); Cu-Cu=7.30 and 7.42 A in [Cu 2 (BTIM) 2 (N 3 ) 2 ](N 3 ) 2 •5H 2 O (II)) and a large separation between the two parallel, eclipsed benzene rings (3.93 A (I), 4.4 and 4.3 A (II)). Variable-temperature magnetism and ESR spectra support the presence of very weak antiferromagnetic exchange between the copper (II) centers in I and II. The crystal and molecular structure of the complex [Cu(LP) 2 ](ClO 4 ) 2 (IV) (LP=1,2-bis(4,5-dihydroimidazol-2-yl)benzene) is also reported. LP represents half of the ligand BTIM. IV crystallized in the monoclinic system, space group P2 1 /n, with a=10.4569 (5) A, b=11.1376 (8) A, c=12.6854 (7) A, β=98.500 (10)°, and two formula units per unit cell. Refinement by full-matrix least squares gave final residuals of R=0.060 and R w =0.067