Magnetic Mn and Co Complexes with a Large Polycyclic Aromatic Substituted Nitronylnitroxide

Abstract

2-(1'-Pyrenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (PyrNN) was reacted with M(hfac)(2) (M = Mn(II) and Co(II), hfac = hexafluoracetylacetonate) to give two isostructural ML(2) stoichiometry M(hfac)(2)(PyrNN)(2) complexes and a ML stoichiometry one-dimensional (1-D) polymer chain complex [Mn(hfac)(2)(PyrNN)]. The ML(2) complexes have similar crystal structures with monoclinic unit cells, in which one NO unit from each PyrNN ligand is bonded to the transition metal on cis vertices of a distorted octahedron. The major magnetic interactions are intracomplex metal-to-radical exchange (J), and intermolecular exchange across a close contact between the uncoordinated NO units (J'). For M = Mn(II) an approximate chain model fit gives g = 2.0, J = (-)125 cm(-1) and J' = (-)49 cm(-1); for M = Co(II), g = 2.4, J = (-)180 cm(-1), and J' = (-)70 cm(-1). Hybrid density functional theory (DFT) computations modeling the intermolecular exchange by using only the radical units across the close contact are in good accord with the estimated values of J'. The chain type complex structure shows solvent incorporation for overall structure [Mn(hfac)(2)(PyrNN)](n)·0.5(CHCl(3))·0.5(C(7)H(16)). Both NO groups of the PyrNN ligand are complexed to form helical chains, with very strong metal to radical antiferromagnetic exchange that gives overall ferrimagnetic behavior.

A Cobalt Pyrenylnitronylnitroxide Single‐Chain Magnet with High Coercivity and Record Blocking Temperature

“…The cobalt–cobalt intrachain distance is 7.482(1) Å. The shortest interchain distance between cobalt(II) ions is a relatively large 11.151(1) Å, similar to that in the analogous isostructural manganese(II) chain (11.40 Å) 15. The crystallographic analysis of [Co(hfac) 2 PyrNN] n showed the substantial volume between individual chains to be occupied by entrained, disordered chloroform and n ‐heptane solvent molecules (for convenience, solvation molecules are not included in naming this complex).…”

“…We recently reported that the PAH‐substituted nitronylnitroxide 2‐(1′‐pyrenyl)‐4,4,5,5‐tetramethyl‐4,5‐dihydro‐1 H ‐imidazole‐3‐oxide‐1‐oxyl (PyrNN) can be incorporated into a twofold helical [Mn(hfac) 2 PyrNN] n chain that has very strong antiferromagnetic exchange interaction between manganese(II) and the radical units, with no evidence of long‐range magnetic order down to 2 K 15. In this article, we report the isostructural cobalt(II) chain complex [Co(hfac) 2 PyrNN] n .…”

(Azulene‐1,3‐diyl)‐bis(nitronyl nitroxide) and (Azulene‐1,3‐diyl)‐bis(iminonitroxide) and Their Copper Complexes

“…The calculated exchange interaction ( J calcd‐contact‐II / k B =−2.4 K) is small relative to the reported exchange interaction ( J / k B =−70 K) of Pyr−NN ⋅⋅⋅ NN−Pyr (Pyr: 1‐pyrenyl) with an intermolecular N−O ⋅⋅⋅ O−N contact of 3.374 Å . The difference between the two systems in the exchange interaction is due to the poor overlap of the nitroxide magnetic orbitals in [Cu(hfac) 2 (IN 2 Az)] ⋅ C 6 H 12 (see Figure S9)…”

Positional Isomers of Tetramethoxypyrene-based Mono- and Biradicals

“…[5][6] Lately the stable aminoxyl radicals attached to several polyaromatic hydrocarbons (PAH) have been synthesized and proved their application in rechargeable batteries, sensors, organic field effect transistors and quantum magnets. [7][8][9][10][11][12] The PAH bearing aminoxyl radical moieties are also found to exhibit photoexcited high spin states.…”