Coupled High Spin Co^II Ions Linked by Symmetrical Double Hydrogen Bonds: Role of a Slowly Relaxing Cu^II Impurity in Interrupting the Co^II–Co^II Exchange Interaction

Abstract

Co II and Cu II ions are two paramagnetic transition metal ions showing different relaxation rates (ν), with ν Co II >> ν Cu II . To measure the isotropic exchange constant (J) between high spin Co II ions and between Cu II ions and high spin Co II ions, we performed magnetic and EPR measurements complemented with computational calculations on pure transdiaqua-bis(picolinato-N,O)-cobalt(II) dihydrate (1), on the Cu II ion doped compound of 1 (2), and on the Cu II ion doped compound in a Zn II matrix isomorphous to 1. The temperature dependence of the Cu II EPR resonance lines of 2 induced by the fast relaxing Co II ion host as well as the evaluation of the temperature-independent Co II -Co II and Cu II -Co II isotropic exchange [a]

Spin Crossover and Fluorine‐Specific Interactions in Metal Complexes of Terpyridines with Polyfluorocarbon Tails

“…However, the small values of the exchange constants are one order of magnitude larger than the hyperfine splitting of complex 5 in an MeCN/PFO mixture, and therefore appear to be enough to cause exchange narrowing of the EPR signals of the complex when this is aggregated in pure MeCN. The magnitude of the exchange coupling (∼0.1–0.2 cm −1 ) transmitted through π‐π interactions between the terpyridine ligands, is much smaller than the values found for systems where the magnetic centers are connected through extended covalent pathways, and even small compared to exchange couplings transmitted through pathways involving H‐bonds [30b] . These values are too small to be observed by standard magnetic measurements, and are usually only revealed by EPR spectroscopy, which is especially suitable to observe very small magnetic interactions.…”

“…For complexes 3 and 5 , no hyperfine splittings could be observed, and the spectra resembled those of exchange‐narrowed extended magnetic systems (Figures 7 and 8). [30b,42] This phenomenon is suggestive of aggregation in solution, likely due to the F$${\cdots }$$ F interactions of the PFC tails. To investigate this further, complexes 3 and 5 were measured in pentafluorobenzonitrile or a solution of acetonitrile/pentafluorobenzonitrile, respectively (Figure S24).…”

EPR, Magnetic, and Computational Characterization of Linear and Zigzag Ladder‐type Chains of Exchange Coupled Cu(II) Complexes with Picolinic and Dipicolinic Acid Ligands

“…Least squares analysis of eq 3 to the data considering the chain model for the dipolar interaction are shown as solid lines in Figures 7; A 1 –A 7 parameters are given in Table 2. Least squares analysis to the data assuming the 3D model (second moment of the dipolar interaction) performed as explained elsewhere [27] yielded A 7 ‐coefficients less than the uncertainty of the method (∼0.1 mT) (not shown), which indicates that neither 1 nor 2 behave as 3D systems regarding the dipolar interaction. The good agreement between fitting and experimental data for 1 indicates a good correlation between magnetism and structure, i. e. structural and magnetic chains are the same.…”

Synthesis, structure, and characterisation of a ferromagnetically coupled dinuclear complex containing Co(ii) ions in a high spin configuration and thiodiacetate and phenanthroline as ligands and of a series of isomorphous heterodinuclear complexes containing different Co : Zn ratios

“…19 The most common experimental techniques for characterising the electronic and magnetic properties of high spin Co( ii ) ions are spectroscopic methods such as UV-vis absorption, magnetic circular dichroism, paramagnetic nuclear magnetic resonance, electron paramagnetic resonance (EPR), and electron-nuclear double resonance, and magnetic techniques such as magnetic susceptibility and magnetisation measurements. 20–40 Characterisation of high spin Co( ii ) ion complexes in different coordination environments with these techniques showed that they present g-values for the S = 3/2 multiplet in the range of 2.1–2.8, and zfs usually greater than 50 cm −1 for hexacoordinated compounds, between 20–50 cm −1 for pentacoordinated compounds and less than 13 cm −1 for tetracoordinated compounds, 41 although some exceptions have been reported. 42–46 Furthermore, the exchange interactions that couple mononuclear Co( ii ) centres in extended lattices are usually below ∼3 cm −1 , and hence usually not detected or poorly discriminated with the most usual experimental techniques, with the only exception being EPR.…”