Complexes with diimine ligands. Syntheses and magnetic behaviour of dinuclear complexes of copper(II), nickel(II) and cobalt(II) with 2,5-bis(2-pyridyl)pyrazine

Abstract

The synthesis, characterization and voltammetric and magnetic behaviour of a series of dinuclear complexes #-(2,5-DPP)[-M(hfacac)2]2, in which hfacac is hexafluoroacetylacetonate, 2,5-DPP is 2,5-bis(2-pyridyl)pyrazine and M = copper(II), nickel(II) and cobalt(II), are described. As with the dinuclear complexes derived from 2,3-bis(2-pyridyl)-pyrazine (2,3-DPP) and analogous ligands, magnetic measurements show that these systems are not coupled. On the basis of magnetic data, we propose that, in contrast to related ligands such as 2,2'-bipyridyl, the coordinated 2,5-DPP cannot be planar.

Origins of stereoselectivity in optically pure phenylethaniminopyridine tris-chelates M(NN′)3n+ (M = Mn, Fe, Co, Ni and Zn)

“…In addition, the spectrum of R C -[CoL 3 3 ][PF 6 ] 2 also contains weak bands at ca 395 nm and 520 nm corresponding to weak MLCT and d-d transitions. 58 This confirms the presence of non-racemic chiral metal centres in solution for this paramagnetic compound, although this cannot be taken as a measure of stereoselectivity. 33 The absence of any observable MLCT bands in the zinc(II), nickel(II) and manganese(II) complexes does not allow for any conclusions to be made about the chirality at these metal centres.…”

“…The lower intensity and the shift to a higher frequency is consistent with the poorer p-donor character of cobalt(II). 58 At higher concentration (1.0 mM), two further signals can be detected at ca 465 nm (e = 80 M -1 cm -1 ) and 535 nm (e = 20 M -1 cm -1 ) corresponding to Laporte-forbidden but spin-allowed d-d transitions.…”

Dipolar and electronic effects on charge transport through single transition metal complexes

“…A hexafluoroacetylacetonate (hfacac) bidentate ligand gives the complex an enhanced stability by fluorine atoms. The complexes I and II with acetyl protection groups at both ends were synthesized according to the previously reported procedure [5,6]. The complex I was expected to exhibit a high dipole moment due to a mixed ligand system with bpy and hfacac.…”

Thermochemistry, singlet–triplet gap and crystal structure of (tetramethylethylenediamine)nickelbis(acetylacetonate) [(TMEDA)Ni(acac)2]

“…Chelating N-adducts of Ni(II) b-diketonates have been studied for a long time [7][8][9][10][11][12][13]. These complexes have been used to study the nature of Ni-ligand interactions and especially the chelate effect has been addressed by experimentally determined thermodynamic data of the coordination reaction [14,15].…”