Stabilization of the Low‐Spin State in a Mononuclear Iron(II) Complex and High‐Temperature Cooperative Spin Crossover Mediated by Hydrogen Bonding |
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| Authors: | Dr. Sipeng Zheng Niels R. M. Reintjens Dr. Maxime A. Siegler Dr. Olivier Roubeau Prof. Elisabeth Bouwman Andrii Rudavskyi Prof. Remco W. A. Havenith Dr. Sylvestre Bonnet |
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| Affiliation: | 1. Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, P.O. Box 9502, Leiden, 2300 RA (The Netherlands);2. Small Molecule X‐ray Facility, Department of Chemistry, Johns Hopkins University, Baltimore, MD 21218 (USA);3. Instituto de Ciencia de Materiales de Aragón (ICMA), CSIC and Universidad de Zaragoza, Plaza San Francisco s/n, 50009 Zaragoza (Spain);4. Theoretical Chemistry, Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen (The Netherlands);5. Stratingh Institute for Chemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands;6. Ghent Quantum Chemistry Group, Department of Inorganic and Physical Chemistry, Ghent University, Krijgslaan 281 (S3), 9000 Gent (Belgium) |
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| Abstract: | The tetrapyridyl ligand bbpya (bbpya=N,N‐bis(2,2′‐bipyrid‐6‐yl)amine) and its mononuclear coordination compound [Fe(bbpya)(NCS)2] ( 1 ) were prepared. According to magnetic susceptibility, differential scanning calorimetry fitted to Sorai’s domain model, and powder X‐ray diffraction measurements, 1 is low‐spin at room temperature, and it exhibits spin crossover (SCO) at an exceptionally high transition temperature of T1/2=418 K. Although the SCO of compound 1 spans a temperature range of more than 150 K, it is characterized by a wide (21 K) and dissymmetric hysteresis cycle, which suggests cooperativity. The crystal structure of the LS phase of compound 1 shows strong N?H???S intermolecular H‐bonding interactions that explain, at least in part, the cooperative SCO behavior observed for complex 1 . DFT and CASPT2 calculations under vacuum demonstrate that the bbpya ligand generates a stronger ligand field around the iron(II) core than its analogue bapbpy (N,N′‐di(pyrid‐2‐yl)‐2,2′‐bipyridine‐6,6′‐diamine); this stabilizes the LS state and destabilizes the HS state in 1 compared with [Fe(bapbpy)(NCS)2] ( 2 ). Periodic DFT calculations suggest that crystal‐packing effects are significant for compound 2 , in which they destabilize the HS state by about 1500 cm?1. The much lower transition temperature found for the SCO of 2 compared to 1 appears to be due to the combined effects of the different ligand field strengths and crystal packing. |
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| Keywords: | cooperative effects hydrogen bonds iron ligand design spin crossover |
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