A versatile dinucleating ligand containing sulfonamide groups

Copper, iron, and gallium coordination chemistries of the new pentadentate bis-sulfonamide ligand 2,6-bis(N-2-pyridylmethylsulfonamido)-4-methylphenol (psmpH3) were investigated. PsmpH3 is capable of varying degrees of deprotonation, and notably, complexes containing the fully trideprotonated ligand can be prepared in aqueous solutions using only divalent metal ions. Two of the copper(II) complexes, [Cu2(psmp)(OH)] and [Cu2(psmp)(OAc)2](-), demonstrate the anticipated 1:2 ligand/metal stoichiometry and show that the dimetallic binding site created for exogenous ligands possesses high inherent flexibility since additional one- and three-atom bridging ligands bridge the two copper(II) ions in each complex, respectively. This gives rise to a difference of 0.4 Å in the Cu···Cu distances. Complexes with 2:3 and 2:1 ligand/metal stoichiometries for the divalent and trivalent metal ions, respectively, were observed in [Cu3(psmp)2(H2O)] and [M(psmpH)(psmpH2)], where M = Ga(III), Fe(III). The deprotonated tridentate N-2-pyridylsulfonylmethylphenolato moieties chelate the metal ions in a meridional fashion, whereas in [Cu3(psmp)2(H2O)] the rare μ2-N-sulfonamido bridging coordination mode is observed. In the bis-ligand mononuclear complexes, one picolyl arm of each ligand is protonated and uncoordinated. Magnetic susceptibility measurements on the doubly and triply bridged dicopper(II) complexes indicate strong and medium strength antiferromagnetic coupling interactions, with J = 234 cm(-1) and 115 cm(-1) for [Cu2(psmp)(OH)] and [Cu2(psmp)(OAc)2](-), respectively (in HHDvV =...+JS1S2 convention). The trinuclear [Cu3(psmp)2(H2O)], in which the central copper ion is linked to two flanking copper atoms by two μ2-N-sulfonamido bridges and two phenoxide bridges shows an overall magnetic behavior of antiferromagnetic coupling. This is corroborated computationally by broken-symmetry density functional theory, which for isotropic modeling of the coupling predicts an antiferromagnetic coupling strength of J = 70.5 cm(-1).