High-Spin Cobalt(II) Complex with Record-Breaking Anisotropy of the Magnetic Susceptibility According to Paramagnetic NMR Spectroscopy Data

Abstract

The tetrahedral cobalt(II) complex [CoL2](HNEt3)2 (I), where L is 1,2-bis(methanesulfonamido)benzene, exhibiting the properties of a single-molecule magnet is synthesized and characterized. The electronic structure parameters of complex I are determined by paramagnetic NMR spectroscopy. They completely reproduce the results of less available methods of studying single-molecule magnets. The value of axial anisotropy of the magnetic susceptibility estimated for complex I (Δχax = 34.5 × 10–32 m3 at 20°C) is record-breaking among all transition metal complexes studied by the NMR method, which provides wide possibilities for the use of complex I as a paramagnetic label for structural biology or as a contrast agent and even a temperature sensor for medical diagnostics. The data obtained indicate the advantages of paramagnetic NMR spectroscopy as a method of investigation of the magnetic properties and electronic structures of highly anisotropic transition metal complexes, which are precursors of many functional materials.

Static and Dynamic Magnetic Properties of a Co(II)‐Complex with N2O2Donor Set – A Theoretical and Experimental Study

“…Complex 1 has further been studied by temperature dependent 1 H NMR in two non‐coordinating solvents: polar CDCl 3 (Figure S5) and non‐polar C 6 D 6 (Figure S6). The temperature dependent chemical shift ( δ ) is opposite for both solvents what might be due to the different extent of ring currents that are produced by the solvent‐solute dipolar interactions (magnetic moments of the nucleus and unpaired electrons) [31] …”

“…The temperature dependent chemical shift (δ) is opposite for both solvents what might be due to the different extent of ring currents that are produced by the solvent-solute dipolar interactions (magnetic moments of the nucleus and unpaired electrons). [31] IR spectroscopy. In the IR spectra of complex 1 (Figure S7), the stretching vibration of the free ligands (ν OH ) 3430-3464 cm À 1 is not observed, suggesting deprotonation of the hydroxyl group and formation of metal-oxygen bonds.…”

Mononuclear Transition Metal Cymantrenecarboxylates as Precursors for Spinel-Type Manganites

“…Complexes containing Co(II) are the most prominent among the 3d-element compounds as potential SMMs. In particular, for the cobalt complexes, the record SMM characteristics among the transition metal complexes were obtained [ 38 , 39 , 40 ]. In this regard, magnetic studies of complexes 1 , 4 , and 5 were carried out in constant and alternating magnetic fields.…”

Observability of Paramagnetic NMR Signals at over 10 000 ppm Chemical Shifts

“…[ 3 , 4 ] At the same time, there is a growing interest in the detection and analysis of paramagnetic intermediates in catalytic reaction cycles, particularly for the first‐row transition metals, where the reactive molecular fragments tend to be either directly bonded, or otherwise in close proximity to the metal. [ 5 , 6 , 7 , 8 , 9 , 10 , 11 ] Other areas of current interest are single‐molecule magnets (SMMs),[ 12 , 13 , 14 , 15 ] contrast agents in magnetic resonance imaging (MRI),[ 16 , 17 , 18 ] and pseudocontact shift (PCS) probes in structural biology. [ 19 , 20 , 21 , 22 ] Several recent studies used magneto‐structural correlations derived by multireference ab initio methods to refine chemical structures using paramagnetic NMR shifts.…”