Cu(II) complexes of a pincer ligand with an anionic central donor and intramolecular H-bonding in the second coordination sphere.

Mononuclear copper(II) chloride complexes of deprotonated N-(di(pyridin-2-yl)methyl)pyridine-2-sulfonamide (dpmps) show that it behaves as a tridentate ligand and is approximately planar, with a non-coordinated second coordination sphere (SCS) pyridyl group. This pyridyl H-bonds with proximal monodentate apical ligands: acting as a H-donor in the structure of [Cu(κ3-Hdpmps)Cl2] and a H-acceptor in [Cu(κ3-dpmps)Cl(ROH)] (R = CH3, CH3CH2). In acetonitrile both complexes are converted to dimeric [Cu2(dpmps)2Cl2] where sulfonyl O atoms coordinate to the second Cu(II) atom and a pyridyl group on each ligand remains uncoordinated. In water, chloride complexes are hydrolyzed and tetranuclear, 1D polymeric and oligomeric complexes can be isolated. A half-field transition at g = 4.2 in the EPR spectrum and two redox processes (0.04 V and -0.16 V vs. AgCl/Ag) indicate that a dimeric species, proposed to be [Cu2(dpmps)2(H2O)2]2+, dominates in aqueous solutions above pH 5-6. DFT calculations support the conclusion that dimerization is energetically favorable. A hypothetical complex in which a HOOH ligand is bound analogously to the isoelectronic and isostructural MeOH in the structurally characterized mononuclear complex is supported by DFT calculations. Such a species is a relevant intermediate for HOOH activation by Cu-containing metalloenzymes.