A New Nitronyl Nitroxide Radical as Building Blocks for a Rare S = 13/2 High Spin Ground State 2p-3d Complex and a 2p-3d-4f Chain

Abstract

A new nitronyl nitroxide radical L (L = 2-(4-(5methyl-carbonyl-3-pyriyl)benzoxo)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) containing N−O groups and the pyridyl nitrogen group was designed and synthesized as a multidentate ligand to obtain compounds with interesting structures and magnetic properties from 3d or 3d-4f precursors. The reaction of Cu(hfac) 2 and/or Gd(hfac) 3 •2H 2 O (hfac = hexafluoroacetylacetonate) with L resulted in a rare S = 13/2 high spin ground state Cu II complex [(Cu(hfac) 2 ) 7 (L) 6 ] (1) and a Cu II − Gd III chain complex [Gd(hfac) 3 Cu(hfac) 2 (L) 2 ] n •0.5CH 2 Cl 2 (2). Single crystal X-ray diffraction studies indicate that the N−O groups of the L radicals are all axially bound to Cu II ions in complex 1, which result in the ferromagnetic exchange between Cu II and radicals and an S = 13/2 high spin ground state. While adding Gd(hfac) 3 units to the system of Cu(hfac) 2 and L radical, a one dimension chain structure is obtained, and there are ferromagnetic Gd III -radical interactions and antiferromagnetic radical−radical coupling in the chain.

2p-3d-4f Heterotrispin Chains and Ring–Chains Bridged by a Nitronyl Nitroxide Ligand: Structure and Magnetic Properties

“…The fit to the magnetic data yields g = 2.07, J 1 = 23.92 cm –1 , J 2 = −6.98 cm –1 , and J 3 = 2.83 cm –1 . The positive J 1 demonstrates the ferromagnetic copper­(II)–nitroxide (axial) exchange, attributing to the orthogonal magnetic orbitals (the π* (radical unit) and the d x 2 – y 2 (Cu­(II) ion) orbitals). , The magnitude of the J 1 is well compared with the exchange interactions found in other Cu II –NIT complexes. − The negative J 2 and positive J 3 are consistent with the antiferromagnetic radical–radical coupling via through the gadolinium­(III) ion and the weak ferromagnetic gadolinium­(III)–nitroxide interaction, respectively, as found in other reported Gd–NIT complexes. , …”

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

“…5,[7][8][9][10][11][12][13]23,24 Cu(hfac) 2 complexes with various derivatives of 3-pyridyl-substituted nitronyl nitroxide (L) are of particular interest due to the diversity of molecular species and their magnetic properties (Scheme 1). 4,7,12,[16][17][18]25,26 Introduction of a Me group in the 4th position of the pyridine ring for L 4-Me nitronyl nitroxide has led to the formation of Cu(II) complexes with structure and magnetic properties completely different from those of the [{Cu(hfac) 2 } 4 L 2 ] compound based on the unsubstituted ligand. 4,12 Recently described copper(II) and mixed-metal copper(II)-lanthanide complexes with L 5-Br and L 6-OMe nitronyl nitroxides have demonstrated various topological structures and different magnetic behaviors in the absence of structural and magnetic transitions.…”

“…4,12 Recently described copper(II) and mixed-metal copper(II)-lanthanide complexes with L 5-Br and L 6-OMe nitronyl nitroxides have demonstrated various topological structures and different magnetic behaviors in the absence of structural and magnetic transitions. [16][17][18]25,26 However, the effect of substituents at different positions of the pyridine ring on the coordination ability of 3-pyridyl nitronyl nitroxide ligand, structure, and magnetic behaviors of the resulting Cu(II) complexes has not been studied systematically. Therefore, the Me group and Br atom were chosen as substituents for the 2nd, 5th, or 6th positions of the pyridine heterocycle of L R nitroxide, because both of them have the same spatial size but different electronic properties (Scheme 1).…”

“…However, only a few Cu­(II) complexes with nitroxides exhibit structural-magnetic anomalies under external stimuli. − Even a minor modification of a ligand leads to significant changes in the molecular and crystal structures of the resulting Cu­(II) complexes. This strongly affects the parameters of magnetic transitions and can result in the assembly of phases that cannot exhibit any magnetostructural anomalies. ,− ,, Cu­(hfac) 2 complexes with various derivatives of 3-pyridyl-substituted nitronyl nitroxide (L) are of particular interest due to the diversity of molecular species and their magnetic properties (Scheme ).…”

“…This strongly affects the parameters of magnetic transitions and can result in the assembly of phases that cannot exhibit any magnetostructural anomalies. ,− ,, Cu­(hfac) 2 complexes with various derivatives of 3-pyridyl-substituted nitronyl nitroxide (L) are of particular interest due to the diversity of molecular species and their magnetic properties (Scheme ). ,,,− ,, Introduction of a Me group in the 4th position of the pyridine ring for L 4‑Me nitronyl nitroxide has led to the formation of Cu­(II) complexes with structure and magnetic properties completely different from those of the [{Cu­(hfac) 2 } 4 L 2 ] compound based on the unsubstituted ligand. , Recently described copper­(II) and mixed-metal copper­(II)-lanthanide complexes with L 5‑Br and L 6‑OMe nitronyl nitroxides have demonstrated various topological structures and different magnetic behaviors in the absence of structural and magnetic transitions. − ,, However, the effect of substituents at different positions of the pyridine ring on the coordination ability of 3-pyridyl nitronyl nitroxide ligand, structure, and magnetic behaviors of the resulting Cu­(II) complexes has not been studied systematically. Therefore, the Me group and Br atom were chosen as substituents for the 2nd, 5th, or 6th positions of the pyridine heterocycle of L R nitroxide, because both of them have the same spatial size but different electronic properties (Scheme ).…”