Transition metal derivatives of a chelating nitronyl nitroxide ligand. Nickel(II) and manganese(II) complexes

Abstract

Complexes of the nitroxide ligand 2-(2-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-l/f-imidazolyl-1 -oxy 3-oxide (NIT2-Py) with NiCl2 (1, CmHjíCIíNíNíO*) and MnCl2 (2, C26H36Cl6MnN604) have been structurally and magnetically characterized. Both complexes are centrosymmetric three-spin systems in which the nitroxyl group is coordinated to the metal ion. Metal-nitroxide interactions of -110 cm-1 for 1 and -80 cm-1 for 2 (H = -2JS¡Sj) are observed. These coupling constants are weaker than usually observed in previously reported examples (<-200 cm-1 for Ni and -150, -200 cm-1 for Mn). This result was rationalized by considering a reduced overlap of the magnetic orbitals due to a peculiar geometric arrangement in the chelate. Comparison to literature reported species is obtained from the homologous hexafluoroacetylacetonates, 3 (C22H18F12N3Ni06) and 4 (C22Hi8F12MnN3C>6), which exhibit similar structural and magnetic properties. Coordination of the nitroxyl group in these derivatives illustrates the use of the chelate effect for designing exchange-coupled nitroxide derivatives of poor electrophilic metal centers. Relevant structural parameters are as follows: 1, monoclinic, P2\¡c, a = 8.890

Crystal structure of diaquabis[2-{2′-[(1′-methyl)benzimidazolyl]}-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide]nickel(II)bisperchlorate dihydrate, [Ni(H2O)2(C15H19N4O2)2][ClO4]2 · 2H2O

“…The axial directions are also slightly deviating from 90°as indicated by the ∠O1-Ni1-O4 of 89.82(4)°and ∠O3-Mn1-N1 of 86.98(4)°.O2-N4-C9-N3-O1 is nearly coplanar but makes adihedral angle of 37.14(9)°with the plane of the benzimidazole ring and 39.99°with the equatorial plane N1-O1-N1A-O1A. Intermolecular hydrogen bonds are found between the coordinating water molecules and ClO 4 -anions (O4-H2W···O8 i , 2.792(3) Å,173.3°,symmetry code i: x+1,y,z), and between the coordinating water molecules and the lattice water molecules (O3-H1W···O9, 2.713(2) Å,166.1°). The intermolecular interactions also occur between the lattice water molecules and ClO 4 -anions (O9-H4W···O7 ii ,2.951(4) Å,130.0°,symmetry code ii: x+1/2,y-1/2,z), and between the lattice water molecules and nitroxide oxygen atoms (O9-H3W···O2…”

“…These radicals are especially attractive due to their donor atoms to assemble aextended arrangement with changing magnetic coupling. Therefore, design of new metal-radical compounds can lead to abetter understanding of magneto-structural correlations, which can facilitate the rational intra-and intermolecular magnetic interactions [4][5][6]. The crystal structure of the title compound consists of [Ni(NIT-1'-MeBzIm) 2 …”

Crystal structure of monoaqua-[2-(4-pyridyl)-4,4,5,5,- tetramethylimidazoline-1-oxyl-3-oxide]-dicyanamidolead(II), Pb(H2O)(C12H16N3O2)2(C2N3)

“…The syntheses of new molecular magnetic materials that combine metal ions and organic radicals as ligating sites have attracted much more attention in the last few years [2][3][4]. Stable Nitronyl nitroxide radicals (NITR), have played aprominent role in the design and construction of molecular magnetic materials.…”

“…The "metal-organic" strategy of combining pyridyl-substituted nitronyl nitroxide with metal has been reported successfully [5][6][7]. The dicyanamide anion [N(CN) 2 ] -can act as aterminal ligand, it can act as abridging ligand [8,9].…”

“…The axial position is occupied by oxygen atom (O5) from water molecule, with the bond length of 2.409(2) Å.The dihedral angle between the pyridyl ring and ON-C-NO moieties is 23.16°.The shortest distance between the two N-Ogroups from NITpPy is 3.633 Å.Inthe complex, the [N(CN) 2 ] -anions act as terminal ligands. N-Pb-Nangles significantly deviate from orthogonal, ranging from 81.76(7)°to 94.51(9)°.The Pb(II) ion has adisplacement of 0.631 Å out of the basal plane.…”