Slow Electronic Relaxation in T52−A11 Spin Equilibria of Tris(2-methyl-1,10-phenanthroline)Iron(II) Complexes: A Mössbauer Effect Study

Abstract

Articles you may be interested inThe effect of pressure on the thermal hysteresis of the firstorder spin transition in bis(1,10 phenanthroline2carbaldehyde phenylhydrazone) iron (II) complexes J. Chem. Phys. 83, 3055 (1985); 10.1063/1.449209 Electron Transfer Rates for Unsubstituted and Dimethylsubstituted Tris(1,10phenanthroline) Iron(II) and (III) Ions from NMR Studies Erratum: Nuclear Magnetic Resonance Studies of Electron Transfer between Tris(2,2′ dipyridyl)osmium(II) and (III) Ions, between Bis(cyclopentadienyl)iron(II) and (III) Ion, and between Tris(1,10phenanthroline)iron(II) and (III) Ions Nuclear Magnetic Resonance Studies of Electron Transfer between Tris (2,2′dipyridyl) osmium (II) and (III) Ions, between Bis(cyclopentadienyl)iron(II) and (III) Ions, and between Tris(1,10 phenanthroline)iron(II) and (III) IonsThe 57Fe Mossbauer effect in [FeL3](CI04). (I) and [FeL3](BF4). (II) ~a~ been studied betwe.en 2~5 and 4.2°K (L=2-methyl-1, lO-phenanthroline). At 295°K, compound I exhibits a quadrupole split pair of lines characteristic of a 5T, ground state, !1EQ(5T,) = 1.03 mm sec-I and 8IBo(5T,) = +0.9.5 m.m sec~l. At 244°K, line broadening is observed. At even lower temperatures, e.g., at 196 K, the relative Intensity of the doublet has decreased and a second doublet typical of a IAI ground state has appeared. At 4.2°K, 72.7% of the intensity is due to IA I , !1EQ(IA I) =0.57 mm secl, and 8 IB (IAI) =0.?8 mm S~C-I. Similar behavior is encountered in II. The observations are accounted for by slow electronIc relaxatIOn between 6T, and lAI in the temperature range between 230 and 120 0 K and the assumpt!on of permanently ~ar~mag netic molecules which become apparent below nOK. A change of the relaxatIOn at about 244 K IS likely. From the temperature dependence of !1EQ(6T,), the axial field splitting is 8=-640 cm-1 in I and?= -58~ cm-~ in II. In conjunction with magneti~ data it is demons~rated t~at.the 5T2-111 ~ner~ separatIOn 8 vanes with temperature: 8=300 cm-1 at 294 K and 8=990 cm I at 9~ K In I and Similarly In II. In an applied field of 50 kG, the sign of V" is positive for the lAI component In both I and II.

Thermally induced spin transition in tris(2-methoxy-1,10-phenanthroline)iron(II) perchlorate. Variable-temperature Moessbauer, magnetic susceptibility, and far-infrared measurements

“…The observations are similar to those made in a study on the polycrystalline compound [Fe(2-CH3phen) 3] (C104)2,2 except that in the present case the spin conversion from high spin (S = 2) to low spin (S = 0) is shifted to higher temperatures, whereas in the 2-CH3phen complex no spin singlet state is observable at room temperature. 3 Similarly to the findings in the 2-CH3phen complex we again observe two high-spin iron(II) resonance doublets besides the lAlg(Oh) ground state in the Mdssbauer spectra. Their electronic nature may be derived from the temperature dependence of the quadrupole splitting by a calculational method originally proposed by Ingalls,13 employing the general expression £9( ) = l-e2Q( 1 -R)<.r~3)°3ia2 [F(5t, 2 0, T)]…”

Energy-Resolved Collision-Induced Dissociation Studies of 1,10-Phenanthroline Complexes of the Late First-Row Divalent Transition Metal Cations: Determination of the Third Sequential Binding Energies

“…These studies show that for the Fe 2+ d 6 configuration in an octahedral field, there is a value for the ligand field strength beyond which the ground state of the Fe 2+ ion changes from a quintet to singlet state. Hence, a spin crossover or spin transition can be expected to be induced when the ligand field strength about the Fe 2+ ion is in the vicinity of this critical value such that minor external perturbations can tip the scales in favor of one or the other for the ground states. , For example, studies of Fe 2+ complexes using Mossbauer spectroscopy indicate that quintet–singlet transitions of ground-state Fe 2+ are temperature dependent. − Other studies have shown that the ligand structure can influence the symmetry of the Fe 2+ ion environment causing spin transition. − Extensive data exist establishing that nearly all six-coordinate Fe 2+ complexes of the type Fe 2+ (Phen) 3 have diamagnetic ground states . In the current studies, the progressive addition of Phen ligands to the Fe 2+ center effects spin pairing in the Fe 2+ ion only on coordination of the third Phen ligand according to B3LYP results.…”

The high-spin (5T2) .dblharw. low-spin (1A1) transition in solid tris(2,2'-bi-2-imidazoline)iron(II) diperchlorate. Hysteresis effects, simultaneous change of spin and lattice characteristics, and order-disorder phenomena of the perchlorate anion

“…A related observation, as far as Mossbauer spectra are concerned, has been made in the compound [Fe(2-CH3phen)3](C104)2 where a considerable broadening of the Mossbauer lines was encountered for the 5T2 phase. 26 This compound is involved in a very gradual high-spin (5T2)low-spin ('A,) transition. Subsequently, the lines were resolved by Fleisch et al27 into two separate 5T2 doublets over the entire temperature range between 4.2 and 295 K. The two doublets have been attributed to two different lattice sites of high-spin iron(II) characterized by a reversal of the orbital ground state, viz.,5A, and 5E, of D3 symmetry.…”