Ligand Structure Effects on Molecular Assembly and Magnetic Properties of Copper(II) Complexes with 3-Pyridyl-Substituted Nitronyl Nitroxide Derivatives

Abstract

Reaction of Cu(hfac)2 with methyl- and bromo-3-pyridyl-substituted nitronyl nitroxides (LR) leads to assemble a diverse set of coordination complexes: mononuclear [Cu(hfac)2L2-Me], binuclear [{Cu(hfac)2}2(H2O)L2-Me], trinuclear [{Cu(hfac)2}3(L6-Br)2], pentanuclear [{Cu(hfac)2}5(L2-Me)2], and [{Cu(hfac)2}5(L2-Me)4], cocrystals [Cu(hfac)2(L2-Br)2]·[Cu(hfac)2(H2O)2] and [Cu(hfac)2(L2-Br)2]·2[Cu(hfac)2H2O], one-dimensional polymers [Cu(hfac)2L2-Br]n and [Cu(hfac)2L6-Br]n, and cyclic dimers [Cu(hfac)2L5-Me]2, [Cu(hfac)2L5-Br]2, and [Cu(hfac)2L6-Me]2. The molecular structures of the obtained complexes are strongly affected by the substituent type and its location in the pyridine heterocycle. Occupation of the second position of the pyridine ring increases the steric hindrance of both imine and nitroxide coordination sites of L2-R, which is favorable for the formation of various conformers and precipitation of complexes with different molecular structures. The pentanuclear [{Cu(hfac)2}5(L2-Me)2] and [{Cu(hfac)2}5(L2-Me)4] complexes do not have prior analogues and are valuable model objects for investigation of the mechanism of formation of various coordination polymers. The arrangement of long Cu–ONO bonds in {CuO6} square bipyramids due to the weakening nitroxide donor site in complexes, based on L2-Me, L2-Br, and L6-Br ligands, results in ferromagnetic exchange interactions between spins of Cu2+ ions and nitroxides. Complexes with substituents that do not considerably affect the coordination ability of ligands (L5-Me, L5-Br, and L6-Me) exhibit strong antiferromagnetic exchange interactions between spins of Cu2+ ions and nitroxides.

Slow magnetic relaxation and selective luminescent probe in a 2p–3d–4f heterotrispin chain

“…Such magnetic behavior is similar to those of other reported copper II -nitroxide complexes. 21 For complex 2, the χ M T value at room temperature is 2.28 cm 3 K mol −1 , slightly higher than the anticipated value of 1.875 cm 3 K mol −1 for two uncoupled radicals (S = 1/2) and three Cu II (S = 1/2) ions with g = 2.0 (Fig. 5).…”

Intermolecular Spin-Crossover-like Phenomenon Sensitive to Applied External Pressure in Heterospin Crystals

“…The synthesis occasionally led to the mononuclear complex [{Cu­(acF6) 2 }­(ImN- m Py) 2 ] or the single crystals of the tetranuclear cyclic dimer α-[{Cu­(acF6) 2 } 4 (ImN- m Py) 2 ] or both . As is well-known, the reactions of the stereochemically nonrigid Cu­(acF6) 2 matrix with polyfunctional nitroxides form many products with various molecular or crystal structures. − The reasonably perfect crystals of different phases can be separated mechanically, as was done in the present study (Figure S1).…”

Two Cu(II)-Nitronyl Nitroxide Complexes Including Cyclic Dimer: Synthesis, Structures and Magnetic Interactions

“…Such investigation is necessary not only for understanding the magnetic exchange mechanism between the metal ion and the radical ligand but also for the developing of novel molecular magnetic materials. Among these metal-NITR complexes, copper (II) compounds are often used as unique objects for investigating the novel structures and the peculiarities of magnetic exchange pathways, for instance, Cu(II)-NITR complexes with different R groups can form mononuclear and polynuclear complexes, as well as one-dimensional and higher dimensional architectures, which result in different magnetic interactions between Cu(II) and NITR radicals [12] [13]. Investigations reveal that if ONCNO of the nitronyl nitroxide group links with Cu(II) ion at axial position, the magnetic property tends to be a ferromagnetic interaction, whereas equatorial coordinates to Cu(II) ion generally prefers to an antiferromagnetic interaction [14] [15] [16].…”