Magnetic Cationic Copper(II) Chains and a Mononuclear Cobalt(II) Complex Containing [Ln(hfac)₄]⁻ Blocks as Counterions

Abstract

Four new heterospin compounds with molecular formula {[Cu 2 (hfac) 3 (TlTrzNIT) 2 ][Ln(hfac) 4 ]} n •C 7 H 16 (Ln III = Gd (1), Tb (2), or Dy (3)) and [Co(hfac)-(TlTrzNIT) 2 ][Dy(hfac) 4 ] ( 4), where hfac is hexafluoroacetylacetonato and TlTrzNIT is the nitronylnitroxide radical 1-(mtolyl)-1H-1,2,3-triazole-4-(4,4,5,5-tetramethylimidazoline-1oxyl-3-oxide), were obtained. All structures were determined by single-crystal X-ray diffraction. In compounds 1−3, the TlTrzNIT radical is bridge-coordinated to copper(II) ions, leading to positively charged copper(II)-radical chains containing [Ln(hfac) 4 ] − as counterions. In compound 4, the cobalt(II) ion is coordinated to two TlTrzNIT radicals and one hfac ligand in bidentate mode leading to a mononuclear cationic complex that contains [Dy(hfac) 4 ] − as counterion. Magnetic measurements of all complexes were performed. Magnetic data were fit considering the contributions of the copper(II)-radical chain and a paramagnetic gadolinium(III) ion for 1. The sign and magnitude of the magnetic coupling constants extracted from the fit were confirmed by density functional theory calculations. The obtained spin topology shows an alternated ferro-antiferromagnetic chain. Field-induced single molecule magnet behavior was observed for the Dy derivatives 3 and 4, in agreement with CASSCF calculations performed for the latter system.

High-Spin and Incomplete Spin-Crossover Polymorphs in Doubly Chelated [Ni(L)2Br2] (L = tert-Butyl 5-Phenyl-2-pyridyl Nitroxide)

“…Copper­(II) radical complexes in which the paramagnetic center of the ligand is directly coordinated to the metal center have been the most studied, and the exchange mechanism has been best described among 3d–2p heterospin compounds, ,, since the magnetic orbitals are well-defined as 3d x 2 – y 2 in a 3d 9 copper­(II) ion and π* in a paramagnetic ligand. The 3d–2p interaction in copper­(II) complexes having a nitroxide radical coordinated at an equatorial site is often reported to be strongly antiferromagnetic, but in fact a strong ferromagnetic interaction is also available. , The exchange interaction is sensitive to the coordination geometry. The couplings sometimes exceed the order of thermal energy of 300 K, even when they are ferromagnetic.…”

Synthesis, Magnetic and High-Field EPR Investigation of Two Tetranuclear NiII-Based Complexes

“…8 One of the strategies for the creation of new cubane complexes is the use of β-diketonates, a widely exploited ligand in molecular magnetism. 11 In a previous article, 12 some of us described the influence of small ligand changes on the magnetic properties of two Co II cubane compounds. S u b s t i t u t i o n o f t h e e t h a n o l m o l e c u l e s i n [Co 4 (tta) 4 (MeO) 4 (EtOH) 4 ] with methanol distorts the Co II coordination spheres, resulting in subtle changes to the bridging angles, leading to a significant change in magnetic behavior.…”

“…One of the strategies for the creation of new cubane complexes is the use of β-diketonates, a widely exploited ligand in molecular magnetism . In a previous article, some of us described the influence of small ligand changes on the magnetic properties of two Co II cubane compounds.…”

High-Frequency EPR Studies of New 2p–3d Complexes Based on a Triazolyl-Substituted Nitronyl Nitroxide Radical: The Role of Exchange Anisotropy in a Cu–Radical System

“…All reagents and solvents were purchased from commercial sources and used without further purifications. [M­(hfac) 2 (H 2 O) 2 ] (M II = Mn, Cu or Co) and the radical TlTrzNIT (Chart ) were synthesized using previously reported methods.…”