Stabilization of the higher oxidation states of nickel. Molecular structure of bis(2,6-diacetylpyridine dioximato)nickel(IV)

Abstract

The nickel(IV) complex, bis(2,6-diacetylpyridine dioximato)nickel(IV), Ni(C9N302H9), has been examined by single-crystal X-ray structural techniques. The crystallographic data are: Laue symmetry 4/m; space group, I4Ja;a = b = 7.745 (3) A, c = 30.510 (16) A; dm = 1.59 (2) g/cm3; dx = 1.600 g/cm3 for four monomeric molecules in the unit cell. The 8371 reflections were measured on an automated Picker four-circle diffractometer and gave 702 unique observations for the structural analysis. Full-matrix least-squares analysis including hydrogen atoms gave final discrepancy factors of R = 0.028 and Rw = 0.025, S = 0.93. The crystallographic and molecular symmetry of the molecule is 4 (SJ with the nickel atom coordinated to two 2,6-diacetylpyridine dioximato ligands via the six nitrogen atoms of these ligands. A comparison of these nickelnitrogen distances with those found in nickel(II) complexes suggests a shortening of 0.17 A in the Ni(IV)-N bond. This average difference of 0.17 A for t2g6 and t2g6eg2 with a change in formal oxidation number of 2 can be compared with the 0.18-A difference reported earlier in the t2gseg2 Co(NH3)62+ and t2g6 Co(NH3)63+ complexes with a change in formal oxidation number of 1.

Chemistry of tetravalent nickel and related species. 3. Characterization and cyclic voltammetry of new [NiN6] species based on tridentate ligands

“…Assuming that, eq 7, is still valid, consistent values of E°'298 can be obtained (Table IV) using n = m = 1 as required by the nickel(III)-nickel(II) couple Ni(RR'T)2+ + e-+ H+ ^Ni(RR'T)(HRR'T) + (10) Unlike the case of the hexadentate chelate system,1 the proton-independent nickel(III)-nickel(II) couple Ni(RR'T)2+ + Ni(RR'T)2 (11) could not be identified in the present work. Formation curve data for the various nickel(II) species (eq 1 and 2) suggests that the deprotonated nickel(II) complex Ni(Me2T)2 becomes the major species only above pH 10.5.…”

Facile and Versatile Synthesis of Polydentate Metal Chelators with Both Amide and Oxime Donor Groups

“…In particular, we are interested in the synthesis of potentially polydentate ligands that include combinations of deprotonateable amide and oxime groups. Amidates tend to stabilize the Ni(III) oxidation state, [1][2][3][4] while oximate ligands tend to stabilize Ni(IV), 1,[5][6][7][8] although there are a few examples of Ni(IV) complexes of amidate ligands 9 and Ni(III) complexes of oximates. 1,10 Thus, ligands with combinations of these donor groups are anticipated to be useful in tuning the high oxidation state chemistry of complexes with nickel and perhaps other metals.…”

Synthesis, crystal structure and biological activity of the nickel(II) complex of 2,6-diacetylpyridinedihydrazone

“…The Ni-N bonds distances (two from pyridine nitrogen and four from the hydrazone nitrogen atoms) range from 1.995(3) to 2.164(3) Å [for Ni(1)-N(2) hydrazone and Ni(1)-N(3) pyridine respectively]. These values are bigger than with those observed in the similar structure of bis(2,6-diacetylpyridine dioximato)nickel(IV) [5,14].…”

“…Divalent transition metals (iron, cobalt, copper) complexes with 2,6-diacetylpyridinedihydrazone ( Figure 1a) and its derivatives have been prepared and characterized by Curry et al [4]. Subsequently, one crystal structure of a nickel complex related to the title complex has been published by Sproul and Stucky [5] (Figure1b). According to this study, the nickel (IV) ion is coordinated to two 2,6-diacetylpyridine dioximato ligands via the six nitrogen atoms of these ligands.…”