title: Self-assembly of dinitrosyl iron units into imidazolate-edge-bridged molecular squares: characterization including Mössbauer spectroscopy.
abstract: Imidazolate-containing {Fe(NO)(2)}(9) molecular squares have been synthesized by oxidative CO displacement from the reduced Fe(CO)(2)(NO)(2) precursor. The structures of complex 1 [(imidazole)Fe(NO)(2)](4), (Ford, Li, et al.; Chem. Commun.2005, 477-479), 2 [(2-isopropylimidazole)Fe(NO)(2)](4), and 3 [(benzimidazole)Fe(NO)(2)](4), as determined by X-ray diffraction analysis, find precise square planes of irons with imidazolates bridging the edges and nitrosyl ligands capping the irons at the corners. The orientation of the imidazolate ligands in each of the complexes results in variations of the overall structures, and molecular recognition features in the available cavities of 1 and 3. Computational studies show multiple low energy structural isomers and confirm that the isomers found in the crystallographic structures arise from intermolecular interactions. EPR and IR spectroscopic studies and electrochemical results suggest that the tetramers remain intact in solution in the presence of weakly coordinating (THF) and noncoordinating (CH(2)Cl(2)) solvents. Mössbauer spectroscopic data for a set of reference dinitrosyl iron complexes, reduced {Fe(NO)(2)}(10) compounds A ((NHC-iPr)(2)Fe(NO)(2)), and C ((NHC-iPr)(CO)Fe(NO)(2)), and oxidized {Fe(NO)(2)}(9) compounds B ([(NHC-iPr)(2)Fe(NO)(2)][BF(4)]), and D ((NHC-iPr)(SPh)Fe(NO)(2)) (NHC-iPr = 1,3-diisopropylimidazol-2-ylidene) demonstrate distinct differences of the isomer shifts and quadrupole splittings between the oxidized and reduced forms. The reduced compounds have smaller positive isomer shifts as compared to the oxidized compounds ascribed to the greater π-backbonding to the NO ligands. Mössbauer data for the tetrameric complexes 1-3 demonstrate larger isomer shifts, most comparable to compound D; all four complexes contain cationic {Fe(NO)(2)}(9) units bound to one anionic ligand and one neutral ligand. At room temperature, the paramagnetic, S = (1)/(2) per iron, centers are not coupled.
authors.affiliation: Department of Chemistry, Texas A&M University, College Station, Texas 77843, USA.
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Hess
authors.forename: Chung-Hung
authors.initials: CH
authors.lastname: Hsieh
authors.forename: Scott M
authors.initials: SM
authors.lastname: Brothers
authors.forename: Michael B
authors.initials: MB
authors.lastname: Hall
authors.forename: Marcetta Y
authors.initials: MY
authors.lastname: Darensbourg
mesh_terms: D018360:Crystallography, X-Ray; D007093:Imidazoles / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D009589:Nitrogen Oxides / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D015204:Spectroscopy, Mossbauer / Q000379:methods*
chemical_list: D007093:Imidazoles; D008024:Ligands; D009589:Nitrogen Oxides; C073661:dinitrosyl iron complex; D007501:Iron
references.citation: Biochemistry. 1995 Apr 25;34(16):5527-35
references.pmid: 7727413
references.citation: Nature. 1995 Feb 16;373(6515):580-7
references.pmid: 7854413
references.citation: Nitric Oxide. 2009 Aug;21(1):1-13
references.pmid: 19366636
references.citation: Inorg Chem. 2010 Sep 6;49(17):7644-6
references.pmid: 20687531
references.citation: J Am Chem Soc. 2010 Jun 16;132(23):7908-18
references.pmid: 20496909
references.citation: Biochemistry. 2002 Dec 24;41(51):15212-23
references.pmid: 12484759
references.citation: J Biol Chem. 1997 Aug 15;272(33):20340-7
references.pmid: 9252338
references.citation: Inorg Chem. 2011 Sep 5;50(17):8541-52
references.pmid: 21823576
references.citation: Inorg Chem. 2006 Aug 21;45(17):6583-5
references.pmid: 16903707
references.citation: Biochemistry. 2010 Aug 31;49(34):7272-81
references.pmid: 20684561
references.citation: Chem Commun (Camb). 2005 Jan 28;(4):477-9
references.pmid: 15654375
references.citation: Phys Rev B Condens Matter. 1986 Jun 15;33(12):8822-8824
references.pmid: 9938299
references.citation: J Am Chem Soc. 2008 Nov 19;130(46):15602-10
references.pmid: 18939795
references.citation: Biochemistry. 1994 Mar 29;33(12):3679-87
references.pmid: 8142366
references.citation: Methods Enzymol. 2008;436:445-61
references.pmid: 18237648
references.citation: J Am Chem Soc. 2009 Jun 17;131(23):7964-5
references.pmid: 19459625
references.citation: Inorg Chem. 2008 Mar 17;47(6):2196-204
references.pmid: 18271533
references.citation: Inorg Chem. 1996 Apr 10;35(8):2176-2183
references.pmid: 11666411
references.citation: Phys Rev A Gen Phys. 1988 Sep 15;38(6):3098-3100
references.pmid: 9900728
references.citation: Inorg Chem. 2006 Jul 24;45(15):6041-7
references.pmid: 16842012
references.citation: Inorg Chem. 2011 Sep 5;50(17):8532-40
references.pmid: 21819054
references.citation: J Am Chem Soc. 2010 Mar 24;132(11):3646-7
references.pmid: 20196538
references.citation: Chem Rev. 2002 Apr;102(4):1155-66
references.pmid: 11942790
references.citation: J Mol Biol. 1982 Sep 15;160(2):181-217
references.pmid: 7175933
references.citation: Inorg Chem. 2007 Jun 11;46(12):5110-7
references.pmid: 17444639
references.citation: Proc Natl Acad Sci U S A. 1975 Apr;72(4):1349-53
references.pmid: 1055410
references.citation: Nature. 1965 Sep 18;207(5003):1246-9
references.pmid: 4287143
references.citation: Chem Commun (Camb). 2005 Mar 7;(9):1122-4
references.pmid: 15726165