1334702-01-0Relevant academic research and scientific papers
Importance of out-of-state spin-orbit coupling for slow magnetic relaxation in mononuclear FeII complexes
Lin, Po-Heng,Smythe, Nathan C.,Gorelsky, Serge I.,Maguire, Steven,Henson, Neil J.,Korobkov, Ilia,Scott, Brian L.,Gordon, John C.,Baker, R. Tom,Murugesu, Muralee
, p. 15806 - 15809 (2011)
Two mononuclear high-spin FeII complexes with trigonal planar ([FeII(N(TMS)2)2(PCy3)] (1) and distorted tetrahedral ([FeII(N(TMS)2)2(depe)] (2) geometries are reported (TMS = SiMe3, Cy = cyclohexyl, depe = 1,2-bis(diethylphosphino)ethane). The magnetic properties of 1 and 2 reveal the profound effect of out-of-state spin-orbit coupling (SOC) on slow magnetic relaxation. Complex 1 exhibits slow relaxation of the magnetization under an applied optimal dc field of 600 Oe due to the presence of low-lying electronic excited states that mix with the ground electronic state. This mixing re-introduces orbital angular momentum into the electronic ground state via SOC, and 1 thus behaves as a field-induced single-molecule magnet. In complex 2, the lowest-energy excited states have higher energy due to the ligand field of the distorted tetrahedral geometry. This higher energy gap minimizes out-of-state SOC mixing and zero-field splitting, thus precluding slow relaxation of the magnetization for 2.
Slow magnetic relaxation in trigonal-planar mononuclear Fe(II) and Co(II) bis(trimethylsilyl)amido complexes - A comparative study
Eichhoefer, Andreas,Lan, Yanhua,Mereacre, Valeriu,Bodenstein, Tilmann,Weigend, Florian
, p. 1962 - 1974 (2014/03/21)
Alternating current magnetic investigations on the trigonal-planar high-spin Co2+ complexes [Li(15-crown-5)] [Co{N(SiMe 3)2}3], [Co{N(SiMe3) 2}2(THF)] (THF = tetrahydrofuran), and [Co{N(SiMe 3)2}2(PCy3)] (Cy = -C 6H13 = cyclohexyl) reveal that all three complexes display slow magnetic relaxation at temperatures below 8 K under applied dc (direct current) fields. The parameters characteristic for their respective relaxation processes such as effective energy barriers Ueff (16.1(2), 17.1(3), and 19.1(7) cm-1) and relaxation times τ0 (3.5(3) × 10-7, 9.3(8) × 10-8, and 3.0(8) × 10-7 s) are almost the same, despite distinct differences in the ligand properties. In contrast, the isostructural high-spin Fe2+ complexes [Li(15-crown-5)] [Fe{N(SiMe3)2}3] and [Fe{N(SiMe3)2}2(THF)] do not show slow relaxation of the magnetization under similar conditions, whereas the phosphine complex [Fe{N(SiMe3)2}2(PCy3)] does, as recently reported by Lin et al. (Lin, P.-H.; Smythe, N. C.; Gorelsky, S. I.; Maguire, S.; Henson, N. J.; Korobkov, I.; Scott, B. L.; Gordon, J. C.; Baker, R. T.; Murugesu, M. J. Am. Chem. Soc. 2011, 135, 15806.) Distinctly differing axial anisotropy D parameters were obtained from fits of the dc magnetic data for both sets of complexes. According to density functional theory (DFT) calculations, all complexes possess spatially nondegenerate ground states. Thus distinct spin-orbit coupling effects, as a main source of magnetic anisotropy, can only be generated by mixing with excited states. This is in line with significant contributions of excited determinants for some of the compounds in complete active space self-consistent field (CASSCF) calculations done for model complexes. Furthermore, the calculated energetic sequence of d orbitals for the cobalt compounds as well as for [Fe{N(SiMe3)2} 2(PCy3)] differs significantly from the prediction by crystal field theory. Experimental and calculated (time-dependent DFT) optical spectra display characteristic d-d transitions in the visible to near-infrared region. Energies for lowest transitions range from 0.19 to 0.35 eV; whereas, for [Li(15-crown-5)][Fe{N(SiMe3)2}3] a higher value is found (0.66 eV). Zero-field 57Fe Moessbauer spectra of the three high-spin iron complexes exhibit a doublet at 3 K with small and similar values of the isomer shifts (δ), ranging between 0.57 and 0.59 mm/s, as well as an unusual small quadrupole splitting (ΔEQ = 0.60 mm/s) in [Li(15-crown-5)][Fe{N(SiMe3)2}3].
Iron complex-catalyzed ammonia-borane dehydrogenation. A potential route toward B-N-containing polymer motifs using earth-abundant metal catalysts
Baker, R. Tom,Gordon, John C.,Hamilton, Charles W.,Henson, Neil J.,Lin, Po-Heng,Maguire, Steven,Murugesu, Muralee,Scott, Brian L.,Smythe, Nathan C.
, p. 5598 - 5609 (2012/05/20)
Ammonia-borane (NH3BH3, AB) has garnered interest as a hydrogen storage material due to its high weight percent hydrogen content and ease of H2 release relative to metal hydrides. As a consequence of dehydrogenation, B-N-containing oligomeric/polymeric materials are formed. The ability to control this process and dictate the identity of the generated polymer opens up the possibility of the targeted synthesis of new materials. While precious metals have been used in this regard, the ability to construct such materials using earth-abundant metals such as Fe presents a more economical approach. Four Fe complexes containing amido and phosphine supporting ligands were synthesized, and their reactivity with AB was examined. Three-coordinate Fe(PCy3)[N(SiMe3)2]2 (1) and four-coordinate Fe(DEPE)[N(SiMe3)2]2 (2) yield a mixture of (NH2BH2)n and (NHBH)n products with up to 1.7 equiv of H2 released per AB but cannot be recycled (DEPE = 1,2-bis(diethylphosphino)ethane). In contrast, Fe supported by a bidentate P-N ligand (4) can be used in a second cycle to afford a similar product mixture. Intriguingly, the symmetric analogue of 4 (Fe(N-N)(P-P), 3), only generates (NH2BH2)n and does so in minutes at room temperature. This marked difference in reactivity may be the result of the chemistry of Fe(II) vs Fe(0).
