Abstract
A series of four isostructural FeII2 complexes, [(TPyA)2Fe2(XL)]2+ (TPyA = tris(2-pyridylmethyl)amine; XL2- = doubly deprotonated form of 3,6-disubstituted-2,5-dianilino-1,4-benzoquinone; X = H, Br, Cl, and F), were synthesized to enable a systematic study of electronic effects on spin crossover behavior. Comparison of X-ray diffraction data for these complexes reveals the sole presence of high-spin FeII at 225 K and mixtures of high-spin and low-spin FeII at 100 K, which is indicative of incomplete spin crossover. In addition, crystal packing diagrams show that these complexes are well-isolated from one another in the solid state, owing primarily to the presence of bulky tetra(aryl)borate counteranions, such that spin crossover is likely not significantly affected by intermolecular interactions. Variable-temperature dc magnetic susceptibility data confirm the structural observations and reveal that 54(1), 56(1), 62(1), and 84(1)% of FeII centers remain high-spin even below 65 K. Moreover, fits to magnetic data provide crossover temperatures of T1/2 = 160(1), 124(1), 121(1), and 110(1) K for X = H, Br, Cl, and F, respectively, along with enthalpies of H = 11.4(3), 8.5(3), 8.3(3), and 7.5(2) kJ/mol, respectively. These parameters decrease with increasing electronegativity of X and thus increasing electron-withdrawing character of XL2-, suggesting that the observed trends originate primarily from inductive effects of X. Moreover, when plotted as a function of the Pauling electronegativity of X, both T1/2 and H undergo a linear decrease. Further analyses of the low-temperature magnetic data and variable-temperature Mössbauer spectroscopy suggest that the incomplete spin crossover behavior in [(TPyA)2Fe2(XL)]2+ is best described as a transition from purely [FeHS-FeHS] (HS = high-spin) complexes at high temperature to a mixture of [FeHS-FeHS] and [FeHS-FeLS] (LS = low-spin) complexes at low temperature, with the number of [FeHS-FeHS] species increasing with decreasing electron-withdrawing character of XL2-.
Original language | English (US) |
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Pages (from-to) | 359-369 |
Number of pages | 11 |
Journal | Inorganic chemistry |
Volume | 54 |
Issue number | 1 |
DOIs | |
State | Published - Jan 5 2015 |
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry
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CCDC 1047770: Experimental Crystal Structure Determination
Park, J. G. (Creator), Jeon, I. (Creator) & Harris, T. D. (Creator), Cambridge Crystallographic Data Centre, 2015
DOI: 10.5517/cc14591n, http://www.ccdc.cam.ac.uk/services/structure_request?id=doi:10.5517/cc14591n&sid=DataCite
Dataset
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CCDC 1047775: Experimental Crystal Structure Determination
Park, J. G. (Creator), Jeon, I. (Creator) & Harris, T. D. (Creator), Cambridge Crystallographic Data Centre, 2015
DOI: 10.5517/cc14596t, http://www.ccdc.cam.ac.uk/services/structure_request?id=doi:10.5517/cc14596t&sid=DataCite
Dataset
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CCDC 1047769: Experimental Crystal Structure Determination
Park, J. G. (Creator), Jeon, I. (Creator) & Harris, T. D. (Creator), Cambridge Crystallographic Data Centre, 2015
DOI: 10.5517/cc14590m, http://www.ccdc.cam.ac.uk/services/structure_request?id=doi:10.5517/cc14590m&sid=DataCite
Dataset