Temperature Dependence of the Crystal Lattice Organization of Coordination Compounds Involving Nitronyl Nitroxide Radicals:  A Magnetic and Structural Investigation

Abstract

Four new mononuclear complexes of formula Cd(PN)(4)(NCS)(2) (A), Cd(PNN)(4)(N(3))(2) (B), Zn(PNN)(4)(N(3))(2) (C), and Zn(PNN)(2)(NCS)(2) (D), where PNN stands for 2-(4-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide and PN for 2-(4-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl, were synthesized and structurally and magnetically characterized. The X-ray structures of compounds B and C were also determined at 90 K. Compounds A[bond]C crystallize in the triclinic space group P 1 macro (No. 2), and D crystallizes in the monoclinic space group P2(1)/m (No. 11). A[bond]C adopt a centrosymmetric distorted octahedral geometry in which the metal ions are bonded to four radical ligands through the nitrogen atom of the pyridyl rings and the azido or thiocyanato ligands occupy the apical positions. Compound D adopts a distorted tetrahedral geometry in which the zinc ion is bonded to two radicals and two thiocyanato ligands. As suggested by their magnetic behavior, the low-temperature X-ray structures of B and C show that these compounds undergo a clear structural change with respect to the room-temperature structures. The experimental magnetic behaviors were perfectly reproduced by a dimer model for A[bond]C and an alternating chain model for D while the sudden breaks observed in the chi(M)T versus T curves for B and C were well accounted for by the high- and low-temperature X-ray structures. For all these complexes the crystal structures favor significant overlap between molecular magnetic orbitals leading to rather strong intermolecular antiferromagnetic interactions.

Synthesis and crystal structure of a new mercury(II) chlorine complex with nitronyl nitroxides, C15H19Cl4Hg2N4O2

“…Nitronyln itroxider adicals (NITR), have played ap rominent role in thed esigna nd construction of molecular magnetic materials, due to their intriguing structural diversity and potential applications. The nitroxide derivatives can be bound to the metal through the oxygen atom of O-N groups, resulting in ag ood variety of transition metal-radical complexes have been synthesized [4][5][6][7]. Nitronyl nitroxide radicals, independently or in combination with metal ions, have been one of the most studied systemsinmolecular magnetism for understanding theradical-radical or metal-radical interactions as well as for synthesizing organic ferromagnets and metal-radical magnetic materials.…”

Crystal structure of catena-bis(μ-dicyanamido)-bis[2-(4-pyridyl)- 4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide-κN)zinc(II) — 2-(4-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (1:2), Zn(C12H16N3O2)2(C2N3)2 · 2C52H64N18O8

“…It has also been documented that dicyanamide can be regarded as an idealligandtoconstructpolymers, due to the rich structural and topological features along with the magnetic properties related to this ligand. On the other hand, the nitronylnitroxide radicals acting as useful paramagnetic building blocks have been extensively used to assemble molecular magnetic materials [4][5][6][7]. Taking advantage of theabilitiesofbothnitroxide radicals andthe above mentioned kind of anions to coordinate transition metals, we are dealing with the use of the dicyanamide anions as bridging ligands.…”

Synthesis, crystal structures and magnetic properties of a radical ligand and its corresponding copper(II) complex

“…), benzimidazolyl substituents have rarely been reported so far [8][9][10][11][12]. Therefore, in order to extend our knowledge of the extremely rich chemistry of such systems, we are devoted to the exploration of new building blocks for molecule-based magnetic materials.…”