1 research outputs found
X‑ray Magnetic Circular Dichroism Investigation of the Electron Transfer Phenomena Responsible for Magnetic Switching in a Cyanide-Bridged [CoFe] Chain
The
cyanide-bridged [CoFe] one-dimensional chain, [Co<sup>II</sup>((<i>R</i>)-pabn)]Â[Fe<sup>III</sup>(Tp)Â(CN)<sub>3</sub>]Â(BF<sub>4</sub>)·MeOH·2H<sub>2</sub>O, where (<i>R</i>)-pabn
= (<i>R</i>)-<i>N</i>2,<i>N</i>(2′)-bisÂ(pyridin-2-ylmethyl)-1,1′-binaphthyl-2,2′-diamine
and Tp = hydrotrisÂ(pyrazolyl)Âborate, exhibits magnetic and electric
bistabilities originating from an electron transfer coupled spin transition
between Fe–CN–Co pairs. The use of L-edge X-ray absorption
spectroscopy (XAS) in combination with L-edge X-ray magnetic circular
dichroism (XMCD) is explored for the investigation of the electronic
structure and magnetization of Co and Fe ions separately, in both
diamagnetic and paramagnetic states. It has been established from
susceptibility results that the switching between diamagnetic and
paramagnetic phases emanates from electron transfer between low spin
FeÂ(II) and CoÂ(III), resulting in low spin FeÂ(III) (<i>S</i> = 1/2) and high spin CoÂ(II) (<i>S</i> = 3/2). The XAS
and XMCD results are consistent with the bulk susceptibility measurements,
where greater detail regarding the charge transfer process is determined.
The Fe–CN–Co electron transfer pathway is highlighted
by a strongly XMCD dependent transition to a cyanide back bonding
orbital, giving evidence for strong hybridization with FeÂ(III) t<sub>2g</sub> orbitals. In addition to thermally induced and photoinduced
switching, [CoFe] is found to exhibit a switching by grinding induced
dehydration. Analysis of XAS shows that on grinding diamagnetic [CoFe],
75% of metal ions lock into the magnetic CoÂ(II)ÂFeÂ(III) phase. Density
functional theory calculations based on the [CoFe] crystal structure
in the magnetic and nonmagnetic phases aid the spectroscopic results
and provide a complementary insight into the electronic configuration
of the [CoFe] 3d shells, quantifying the change in ligand field around
Co and Fe centers on charge transfer