title: Synthesis and electronic structure determination of N-alkyl-substituted bis(imino)pyridine iron imides exhibiting spin crossover behavior.
abstract: Three new N-alkyl substituted bis(imino)pyridine iron imide complexes, ((iPr)PDI)FeNR ((iPr)PDI = 2,6-(2,6-(i)Pr(2)-C(6)H(3)-N═CMe)(2)C(5)H(3)N; R = 1-adamantyl ((1)Ad), cyclooctyl ((Cy)Oct), and 2-adamantyl ((2)Ad)) were synthesized by addition of the appropriate alkyl azide to the iron bis(dinitrogen) complex, ((iPr)PDI)Fe(N(2))(2). SQUID magnetic measurements on the isomeric iron imides, ((iPr)PDI)FeN(1)Ad and ((iPr)PDI)FeN(2)Ad, established spin crossover behavior with the latter example having a more complete spin transition in the experimentally accessible temperature range. X-ray diffraction on all three alkyl-substituted bis(imino)pyridine iron imides established essentially planar compounds with relatively short Fe-N(imide) bond lengths and two-electron reduction of the redox-active bis(imino)pyridine chelate. Zero- and applied-field Mössbauer spectroscopic measurements indicate diamagnetic ground states at cryogenic temperatures and established low isomer shifts consistent with highly covalent molecules. For ((iPr)PDI)FeN(2)Ad, Mössbauer spectroscopy also supports spin crossover behavior and allowed extraction of thermodynamic parameters for the S = 0 to S = 1 transition. X-ray absorption spectroscopy and computational studies were also performed to explore the electronic structure of the bis(imino)pyridine alkyl-substituted imides. An electronic structure description with a low spin ferric center (S = 1/2) antiferromagnetically coupled to an imidyl radical (S(imide) = 1/2) and a closed-shell, dianionic bis(imino)pyridine chelate (S(PDI) = 0) is favored for the S = 0 state. An iron-centered spin transition to an intermediate spin ferric ion (S(Fe) = 3/2) accounts for the S = 1 state observed at higher temperatures. Other possibilities based on the computational and experimental data are also evaluated and compared to the electronic structure of the bis(imino)pyridine iron N-aryl imide counterparts.
authors: Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853, USA.
authors: Amanda C
authors: AC
authors: Bowman
authors: Carsten
authors: C
authors: Milsmann
authors: Eckhard
authors: E
authors: Bill
authors: Zoë R
authors: ZR
authors: Turner
authors: Emil
authors: E
authors: Lobkovsky
authors: Serena
authors: S
authors: DeBeer
authors: Karl
authors: K
authors: Wieghardt
authors: Paul J
authors: PJ
authors: Chirik
mesh_terms: D018360:Crystallography, X-Ray; D004583:Electrons; D005290:Ferric Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D005296:Ferrous Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D007094:Imides / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D011725:Pyridines / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D005290:Ferric Compounds; D005296:Ferrous Compounds; D007094:Imides; D011725:Pyridines; C023666:pyridine