Magneto-structural studies of monohydroxo-bridged dicopper(II) complexes M[Cu2L2(OH)]center dot 2H(2)O (M = Na+ (1) and K+ (2); H2L=2,6-bis[N-(phenyl)carbamoyl]pyridine). Effect of Cu-OH-Cu bridge angle on antiferromagnetic coupling

Using a tridentate bis-amide ligand 2,6-bis[N-(phenyl)carbamoyl]pyridine (H 2L), in its deprotonated form, two new monohydroxo-bridged dicopper(II) com plexes M[Cu2L2(OH)]. 2H(2)O (M = Na+ (1) and K+ (2)) have been prepared and characterised by a number of methods, including X-ray crystallography, Eac h copper(II) ion is terminally coordinated by one pyridyl and two amide nit rogen donors. The two copper(II) centres are bridged by a hydroxo group, wi th each copper(II) centre assuming a distorted square planar geometry. The observation of short Cu-N-py and long Cu-N-amide bonds is caused by the ste ric requirement of the ligand. Interestingly, each cation Na+/K+ is coordin ated to four different [Cu2L2(OH)](-) units through the amide O-donors, ill an uncommon distorted tetrahedral coordination environment. Temperature-de pendent magnetic susceptibility measurements revealed that the compounds ha ve S = 0 ground state with singlet-triplet energy separation, 2J = -334 and -296 cm(-1) for 1 and 2, respectively. The larger Cu-OH-Cu bridge angle in 1 (131.1(6)degrees) causes better antiferromagnetic exchange coupling than that in 2 (125.7(6)degrees). (C) 2000 Elsevier Science Ltd. All rights res erved.