The effects of pressure on valence tautomeric transitions of dinuclear cobalt complexes

Abstract

The effects of pressure on valence trautomeric transition behavior of two complexes, [{Co(tpa)}2(dhbq)].(PF6)3 (.(PF6)3) and [{Co(dpqa)}2(dhbq)](PF6)3 (II x (PF6)3) (tpa = tris(2-pyridylmethyl)amine, dpqa = di(2-pyridylmethyl)-N-(quinolin-2-ylmethyl)amine and dhbq = deprotonated 2,5-dihydroxy-1,4-benzoquinone), in the light of changes of magnetic susceptibilities were investigated; the results show that external pressure makes the SC + ET transition process of the two complexes into a general SC process only.

Magnetic properties of a mononuclear iron(II) complex with a typical FeN6coordination octahedron

“…The synthesis of dpqa was carried out according to the literature method of Li and co-workers Li, Yang et al, 2008). For the synthesis of the mononuclear complex, FeSO 4 Á7H 2 O (0.1 mmol) and KSCN (0.2 mmol) were dissolved in methanol (5 ml), then ascorbic acid (5 mg) was added to the solution to avoid oxidation of the Fe II ion.…”

“…This ligand possesses many advantages as a terminal ligand coordinated to metal atoms, namely its stability, strong coordination ability and multiple opportunities forinteractions. Considering the important role ofinteractions in affecting SCO behaviour, and in order to investigate systematically the relationship between SCO behaviour and noncovalent (-) interactions, the new tripodal ligand bis(pyridin-2-ylmethyl)(quinolin-2-ylmethyl)amine (dpqa; see Scheme) Li, Yang et al, 2008), which possesses the possibility of strongerinteractions, has been introduced to construct new mononuclear iron(II) compounds with the typical FeN 6 coordination octahedron. Herein, a new mononuclear iron(II) complex using this ligand, [Fe(NCS) 2 (dpqa)], (I), has been synthesized and structurally characterized.…”

Magnetism and variable temperature and pressure crystal structures of a linear oligonuclear cobalt bis-semiquinonate

“…This can be explained by the fact that the ls-Co(III)-cat state exhibits significantly shorter Co-ligand bond distances, and is thus the more stable form at higher pressures. [18][19][20][21] Besides external pressure, chemically pressure induced by ligand constraints or solvents being present in the crystal lattice is also possible. 22,23 Other interesting effects have been reported recently, such as VT transition triggered by the application of strong magnetic fields, or the theoretically predicted VT upon application of an electric field.…”

Hypersensitive pressure-dependence of the conversion temperature of hysteretic valence tautomeric manganese–nitronyl nitroxide radical 2D-frameworks

“…4 Valence tautomerism is an alternative to spin-crossover (SCO), with which it shares several similarities. [4][5][6][7] Most reports on VT compounds deal with conversions triggered by temperature variations, with a smaller number of studies on the effect of pressure [8][9][10][11][12] or electric field variations. 13 Most VT compounds are based on dioxolene derivatives as redoxactive ligands 4,7,14 and only a few examples use free radicals such as verdazyl 15 or nitronyl nitroxide, as in manganese coordination compounds we recently documented.…”

“…These results show that the magnetic behaviors and redox forms of compounds 1 and 2 are hypersensitive to small changes in external applied pressure and far more than other VT compounds. [8][9][10][11] The cell volume of compounds 1 and 2 has been determined by X-ray analyses at variable temperature in our previous work. 16,17 They are equal to 2037 and 2047 Å 3 for the high temperature redox form and to 1974 and 1944 Å 3 for the low temperature redox form for 1 and 2 respectively.…”