Synthesis, Structure, and Magnetic Properties of Transition Metal Complexes of the Nitroxide 2,5-Dihydro-4,5,5-trimethyl-2,2-bis(2-pyridyl)imidazole-1-oxyl

Abstract

With the radical 2,5-dihydro-4,5,5-trimethyl-2,2-bis(2-pyridyl)imidazole-1-oxyl (L) a series of transition metal complexes have been prepared: [ML(2)](SbF(6))(2) with M(2+) = Mn(2+) (1), Fe(2+) (2), Co(2+) (3), Ni(2+) (4), Cu(2+) (5), and Zn(2+) (6), Cu(L)(Cl)(2)(MeOH) (7), and Cu(L)SO(4).H(2)O (8). The structures of 1, 3, and 6 were determined by X-ray structural analyses. In these compounds the tridendate L is coordinated to the metal ion by the two pyridine nitrogen donors and by the oxygen atom of the nitroxide group. The N-O bond distances are 1.25(2) Å (1), 1.267(13) Å (3), and 1.260(11) Å (6). The M-O-N angles are 117.0(10) degrees (1), 114.5(8) degrees (3), and 114.2(7) degrees (6). Crystal data: space group P2(1)/n, for 1, 3, and 6; compound 1, a = 10.806(3) Å, b = 14.101(6) Å, c = 14.253(4) Å, beta = 108.82(2) degrees, V = 2055.7(12) Å(3), Z = 2, R(1) = 0.0677, wR(2) = 0.1512. Compound 3, a = 10.761(4) Å, b = 14.253(6) Å, c = 14.108(5) Å, beta = 111.16(3) degrees, V = 2017.9(13) Å(3), Z = 2, R(1) = 0.0702, wR(2) = 0.1460; compound 6, a = 10.788(2) Å, b = 14.147(3) Å, c = 14.196(3) Å, beta = 109.93(3) degrees, V = 2036.8(7) Å(3), Z = 2, R(1) = 0.0573, wR(2) = 0.1194. Magnetic measurements of 1, 2, 5, and 8 show strong antiferromagnetic interaction between the spin of the metal ion and the spin of the radical which increases at lower temperatures. For 6 the magnetic moment corresponds to two noninteracting spins in the temperature range 60-300 K.

Lanthanide Complexes with Tripodal Ligands

“…However, till now only three tripodal nitroxyl radical functionalized by pyridyl groups (Figure 6) are known [25,136]. The complexes of the 3d metal ions with the radical tripods 34-36 are most of a sandwich type [25][26][27][28][29][30][31][32]137]), while a number of semi-sandwich Ln-complexes were recently synthesized [138,139] (Figure 7-37). In contrast to the tetradentate tripods of TPA described above, the tripodal oxazolidine radical (Rad) 35 is sterically rigid, forming a pyramid upon coordination with an almost right triangle at the face for both monoradical (37) and biradical complexes (38) (Figure 7) [138,140].…”

The Tripodal Ligand’s 4f Complexes: Use in Molecular Magnetism

“…However, till now, only three tripodal nitroxyl radicals functionalized by pyridyl groups (Scheme 1) are known [25,136]. The complexes of 3D metal ions with the radical tripods 34-36 are mostly sandwich types [25][26][27][28][29][30][31][32]137]), while a number of semisandwich Ln complexes (37) have recently been synthesized [138,139] (Figure 7). In contrast to the tetradentate TPA tripods described above, the tripodal oxazolidine radical (Rad) 35 is sterically rigid.…”