Abstract
Bis(formazanate)iron(II) complexes undergo a thermally induced S = 0 to S = 2 spin transition in solution. Here we present a study of how steric effects and π-stacking interactions between the triarylformazanate ligands affect the spin-crossover behavior, in addition to electronic substituent effects. Moreover, the effect of increasing the denticity of the formazanate ligands is explored by including additional OMe donors in the ligand (7). In total, six new compounds (2-7) have been synthesized and characterized, both in solution and in the solid state, via spectroscopic, magnetic, and structural analyses. The series spans a broad range of spin-crossover temperatures (T1/2) for the LS ⇌ HS equilibrium in solution, with the exception of compound 6 which remains high-spin (S = 2) down to 210 K. In the solid state, 6 was shown to exist in two distinct forms: a tetrahedral high-spin complex (6a, S = 2) and a rare square-planar structure with an intermediate-spin state (6b, S = 1). SQUID measurements, 57Fe Mössbauer spectroscopy, and differential scanning calorimetry indicate that in the solid state the square-planar form 6b undergoes an incomplete spin-change-coupled isomerization to tetrahedral 6a. The complex that contains additional OMe donors (7) results in a six-coordinate (NNO)2Fe coordination geometry, which shifts the spin-crossover to significantly higher temperatures (T1/2 = 444 K). The available experimental and computational data for 7 suggest that the Fe···OMe interaction is retained upon spin-crossover. Despite the difference in coordination environment, the weak OMe donors do not significantly alter the electronic structure or ligand-field splitting, and the occurrence of spin-crossover (similar to the compounds lacking the OMe groups) originates from a large degree of metal-ligand π-covalency.
Original language | English |
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Pages (from-to) | 2045-2055 |
Number of pages | 11 |
Journal | Inorganic Chemistry |
Volume | 60 |
Issue number | 3 |
Early online date | 19-Jan-2021 |
DOIs | |
Publication status | Published - 1-Feb-2021 |
Keywords
- SQUARE-PLANAR
- FORMAZANATE LIGANDS
- IRON(II) COMPLEXES
- STATE
- STEREOCHEMISTRY
- BETA
- REACTIVITY
- COBALT(II)
- REDUCTION
- ANALOGS
Datasets
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CCDC 2036149: Experimental Crystal Structure Determination
Milocco, F. (Contributor), de Vries, F. (Contributor), Siebe, H. (Contributor), Engbers, S. (Contributor), Demeshko, S. (Contributor), Meyer, F. (Contributor) & Otten, E. (Contributor), University of Groningen, 8-Oct-2020
DOI: 10.5517/ccdc.csd.cc26bs7l
Dataset
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CCDC 2036151: Experimental Crystal Structure Determination
Milocco, F. (Contributor), de Vries, F. (Contributor), Siebe, H. (Contributor), Engbers, S. (Contributor), Demeshko, S. (Contributor), Meyer, F. (Contributor) & Otten, E. (Contributor), University of Groningen, 8-Oct-2020
DOI: 10.5517/ccdc.csd.cc26bs9n
Dataset
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CCDC 2036148: Experimental Crystal Structure Determination
Milocco, F. (Contributor), de Vries, F. (Contributor), Siebe, H. (Contributor), Engbers, S. (Contributor), Demeshko, S. (Contributor), Meyer, F. (Contributor) & Otten, E. (Contributor), University of Groningen, 8-Oct-2020
DOI: 10.5517/ccdc.csd.cc26bs6k
Dataset