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 = GaIII, FeIII. 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.