X‑ray Magnetic Circular Dichroism Investigation of the Electron Transfer Phenomena Responsible for Magnetic Switching in a Cyanide-Bridged [CoFe] Chain Michael L. Baker, ‡ Yasutaka Kitagawa, † Tetsuya Nakamura, § Kou Tazoe, ‡ Yasuo Narumi, ‡ Yoshinori Kotani, § Fumichika Iijima, ∥ Graham N. Newton, ∥ Mitsutaka Okumura, † Hiroki Oshio, ∥ and Hiroyuki Nojiri* ,‡ ‡ Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan † Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan § Japan Synchrotron Radiation Research Institute/SPring-8, Sayo, Hyogo 679-5198, Japan ∥ Graduate School of Pure and Applied Sciences, Department of Chemistry, University of Tsukuba, Tennodai 1-1-1, Tsukuba 305-8571, Japan * S Supporting Information ABSTRACT: The cyanide-bridged [CoFe] one-dimensional chain, [Co II ((R)-pabn)][Fe III (Tp)(CN) 3 ](BF 4 )·MeOH·2H 2 O, where (R)-pabn = (R)-N2,N(2′)-bis(pyridin-2-ylmethyl)-1,1′- binaphthyl-2,2′-diamine and Tp = hydrotris(pyrazolyl)borate, 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 Fe(II) and Co(III), resulting in low spin Fe(III) (S = 1/2) and high spin Co(II) (S = 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 Fe(III) t 2g 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 Co(II)Fe(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. ■ INTRODUCTION The manipulation of metal-to-metal charge transfer (MMCT) within magnetic complexes inspires the design of new multifunctional magnetic systems. 1 In such compounds, sensitivity to changes in redox potential between ion pairs is exploited for the control of electronic properties. MMCT and its accompanying switching of magnetic and electronic properties can be controlled by external stimuli such as photoillumination, heat, and pressure. 2 The study of Prussian blue analogues, a class of cyanide-bridged polynuclear materials, has shown considerable success in the pursuit of switchable magnetic phenomena. 3 Recent work has focused on discrete analogues 4 of heterometallic cyanide bridged complexes and has led to the emergence of one-dimensional systems. 5 The synthesis of one-dimensional MMCT systems exhibiting single chain magnet properties 6 in conjunction with switchable magnetism is the focus of much research in the search for advanced functionality within magnetic compounds. Here we investigate a one-dimensional square wave shaped cobalt−cyanide−iron chain, [Co II ((R)-pabn)][Fe III (Tp)- (CN) 3 ](BF 4 )·MeOH·2H 2 O, abbreviated [CoFe] (see Figure 1), where (R)-pabn = (R)-N2,N(2′)-bis(pyridin-2-ylmethyl- 1,1′-binaphthyl-2,2′-diamine and Tp = hydrotris(pyrazolyl)- borate. The structure exhibits chirality originating from the (R)- pabn ligand. The system has received much attention for its multifunctional magnetic and electronic properties, which include the exhibition of single chain magnetism, diamagnetism, Received: June 25, 2013 Published: December 4, 2013 Article pubs.acs.org/IC © 2013 American Chemical Society 13956 dx.doi.org/10.1021/ic402580n | Inorg. Chem. 2013, 52, 13956−13962