Dinuclear metal phosphonates and -phosphates

Abstract

The reaction of Cu(II) or Cd(II) salts with 2,4,6- iPr 3C 6H 2PO 3H 2, 2,4,6- iPr 3C 6H 2CH 2PO 3H 2 or 2,6- iPr 2C 6H 3OPO 3H 2 in the presence of strong chelating nitrogen ligands such as 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), 2-pyridylpyrazole (pypz) or 3,5-dimethyl pyrazole (dmpz) as the ancillary ligands afforded dinuclear copper or cadmium complexes [Cu 2(2,4,6- iPr 3C 6H 2PO 3H) 4(bpy) 2] (4), [Cu 2(2,6- iPr 2C 6H 3OPO 3H) 2(bpy) 2(OAc) 2(CH 3OH) 2]·(CH 3OH) (5), [Cd 2(2,6- iPr 2C 6H 3OPO 3H) 4 (bpy) 2(CH 3OH) 2]·2(CH 3OH) (6), [Cd 2(2,6- iPr 2C 6H 3OPO 3H) 4(phen) 2] (7), [Cu 2(2,6- iPr 2C 6H 3OPO 3H) 2(PyPz) 2(CH 3OH) 2] (8) and [Cu 2(2,4,6- iPr 3C 6H 2CH 2PO 3H) 2(DMPz) 2Cl 2]·(CH 3OH) (9) The molecular structures of 4–7 are grossly similar. The common structural features in these complexes are that the two metal centers are bridged by two bidentate [RPO 2(OH)] − ligands generating a central eight-membered ring. Each of the metal centers also contains a chelating nitrogen ligand and a monodentate phosphonate or a phosphate ligand. In 5 and 6 other terminal ancillary ligands are also present. In compound 8, each of the two copper centers contains a monodentate [RPO 2(OH)] − ligand along with a molecule of methanol. The two coppers are bridged by two monoanionic pyridylpyrazole ligands. The molecular structure of 9 is similar to that of 4–7. However, in 9 each of the two copper centers contain only terminal monodentate ligands in the form of two chlorides and a pyrazole. Magnetic studies on all of these copper complexes reveal an anti-ferromagnetic behavior at low temperatures. In addition, these complexes were found to be artificial nucleases and can convert supercoiled pBR322 DNA form I into nick form II in 1 min in the presence of an external oxidant through a hydrolytic and/or an oxidative pathway.