Syntheses, structures, magnetic, and spectroscopic properties of cobalt(ii), nickel(ii) and zinc(ii) complexes containing 2-(6-methyl)pyridyl-substituted nitronyl and imino nitroxide†

Abstract

Chelate complexation of 4,4,5,5-tetramethyl-2-(6-methyl-2-pyridyl)imidazolin-1-oxyl 3-oxide (NITmepy) and 4,4,5,5-tetramethyl-2-(6-methyl-2-pyridyl)imidazolin-1-oxyl (IMmepy) to cobalt() chloride (bromide) or zinc() chloride afforded tetrahedral four-co-ordinate (T -4) complexes, [MX 2 (NITmepy)] and [MX 2 (IMmepy)] (MX = CoCl (1 and 2), CoBr (1Br and 2Br) or ZnCl (3 and 4), respectively) containing either a six-or a five-membered chelate ring as determined by single-crystal X-ray analysis. The formation of such T -4 complexes arises from the steric requirements of the methyl group at the o-position of the pyridyl-N donor. The UV-vis-NIR spectra suggest that both complexes 1 and 2 in dichloromethane retain their solid state structure. In acetonitrile, however, 1 exists as an equilibrium mixture due to dissociation of the co-ordinated NITmepy, while 2 is stable. The ligand-field spin-allowed and spin-forbidden d-d transitions of 1 and 2 are not influenced by the coordinated radical ligands. The reaction of nickel() chloride and thiocyanate with IMmepy gave a dichloro-bridged dinuclear complex with a square pyramidal five-co-ordinate (SPR-5) geometry and an OC-6 complex, respectively, [{NiCl(IMmepy)} 2 (µ-Cl) 2 ] ( 5) and [Ni(NCS) 2 (IMmepy) 2 ] (6). The intramolecular magnetic interactions in 1 and 2 are estimated to be antiferromagnetic, whereas 5 and 6 give ferromagnetic interactions. Complex 3, with one-dimensional columns, forms a dimer so that a moderate intermolecular antiferromagnetic coupling is demonstrated, while complex 4 exists as a discrete molecule in the crystal and shows paramagnetic behaviour.

Metal complexes of 3-thiophene carboxamides containing a pyridine ring

“…The C-O bond distance is elongated to 1.258(3) Å and the ligand bite angle is 102.11(7)°, the largest of any of the complexes, consistent with the tetrahedral geometry. The Co-O, CoN, and Co-Cl bond distances in 10 (1.963(2) Å, 2.044(2) Å, 2.340(7) Å and 2.2500(7) Å, respectively) are comparable to those reported for the tetrahedral complex [CoCl 2 (NITMepy)] [41].…”

Two Novel Diamagnetic-metal Coordination Polymers of Nitronyl Nitroxide Radical Incorporating Isophthalate Bridges

“…Several studies have shown that antiferro-or ferromagnetic interactions were operative through the central metal ions, such as Ti(IV), Cu(I), Ag(I), Hg(II), Zn(II) and Cd(II) [24][25][26][27][28][29][30][31][32][33][34][35][36][37]. In these complexes, the metal ions play an active role in aiding the exchange coupling between the radicals.…”

Synthesis, crystal structure and magnetism of two cobalt(II) complexes with imino and nitronyl nitroxides

“…By using this approach, various highly interesting species such as molecular-based ferromagnets [5][6][7], single-chain magnets (SCMs) [8][9][10][11][12][13], single-molecule magnets (SMMs) [14][15][16][17][18][19] and molecule spin transition species [20][21][22][23] have been achieved so far. However, most of the work performed in this area has involved in copper(II), nickel(II), manganese(II) or lanthanide compounds, and the reported cobalt(II)-radical compounds are currently very scarce [24][25][26]. It is well known that the high-spin cobalt(II) atom may exhibit large magnetic anisotropy due to strong spin-orbital coupling.…”