Cobalt(II), nickel(II) and zinc(II) coordination chemistry of the N,N′-disubstituted hydroxylamine-(diamido) ligand, 3,3′-(hydroxyazanediyl) dipropanamide

Although directly relevant to metal mediated biological nitrification and the coordination chemistry of peroxide, the transition metal complexes of hydroxylamines and their functionalized variants remain mainly unexplored except vanadium(V) and molybdenum(VI). Reaction of the chelating hydroxylamine ligand 3,3'-(hydroxyazanediyl)dipropanamide (Hhydia) with [M-II(CH3COO)(2)]center dot xH(2)O (M = C-II, Z(II)) in methyl alcohol solution yields the complexes [Co-II(eta(1):eta(1)-CH3COO)(eta(1)-CH3COO)(Hhydia)], (1) and [Zn-II(eta(1)-CH3COO)(2)(Hhydia)], (4), while reaction of Hhydia with trans-[(NiCl2)-Cl-II(H2O)(4)]center dot 2H(2)O yields [Ni-II(Hhydia)(2)]Cl-2 (3). The X-ray structure analysis of 1 and 4 revealed that the Co-II and Z(II) atoms are bonded to a neutral tridentate O,N,O-Hhydia ligand and a chelate and a monodentate acetate groups in a severely distorted octahedral geometry for 1 and two monodentate acetate groups for 4 in a highly distorted trigonal bipyramidal geometry (tau = 0.63). The X-ray structure analysis of 3 revealed that the nickel atom in [Ni-II(Hhydia)(2)](2+) is bonded to two neutral tridentate O,N,O-Hhydia ligands. The twist angle, theta, in [Ni-II(Hhydia)(2)](2+) is 55.1(2)degrees, that is, very close to an ideal octahedron. The metal/Hhydia complexes were studied by UV-Vis (cobalt and nickel compounds), NMR (zinc compounds), HR-MS spectroscopy. The H-1 and C-13 NMR spectra of the methyl alcohol or acetonitrile solutions of Z(II)-Hhydia complexes show the existence of both the 1:1 and 1:2 metal:ligand species being in dynamic equilibrium. The exchange processes between the Zn-II-Hhydia is through complete dissociation-association of the ligand from the complexes as it is evident from the 2D {H-1} EXSY NMR spectroscopy. UV-Vis spectroscopy of the Co-II-Hhydia in methyl alcohol also shows the existence of both the 1:1 and 1:2 metal:ligand species in contrast to 1:2 complex INiII(Hhydia)(2)](2+) which is the only species found in solution. The NMR and UV-Vis observations are additionally supported by the HR-MS studies. (C) 2018 Elsevier Ltd. All rights reserved.