title: Synthesis and characterization of homo- and heterodinuclear M(II)-M'(III) (M(II) = Mn or Fe, M'(III) = Fe or Co) mixed-valence supramolecular pseudo-dimers. The effect of hydrogen bonding on spin state selection of M(II).
abstract: Reaction of H(3)L(1), the Schiff base condensate of tris(2-aminoethyl)amine with three equivalents of 5-methyl-1H-pyrazole-3-carboxaldehyde, with manganese(II)perchlorate or iron(II)tetrafluoroborate results in the isolation of [MH(3)L(1)]X(2) (M = Mn and X = ClO(4) and M = Fe and X = BF(4)). These complexes are high spin d(5) and d(6), respectively, as inferred from the long M-N bond distances obtained by single crystal X-ray diffraction for both and variable temperature magnetic susceptibility and Mössbauer spectroscopy for the iron complex. Aerobic treatment of a solution of [CoH(3)L(1)](2+) with three equivalents of potassium hydroxide produced [CoL(1)]. Homonuclear pseudo-dimers were prepared by the aerobic reaction of [FeH(3)L(1)](BF(4))(2) with 1.5 equivalents of potassium hydroxide to give {[FeH(1.5)L(1)](BF(4))}(2) or by the metathesis reaction of [FeH(2)L(1)][FeHL(1)](ClO(4))(2) with sodium hexafluorophosphate to give [FeH(3)L(1)][FeL(1)](PF(6))(2). The complexes were characterized by EA, IR, ESI-MS, variable temperature single crystal x-ray diffraction and Mössbauer spectroscopy. The iron(III) atom is low spin while the iron(II) atom is spin crossover. Heteronuclear pseudo-dimers were prepared by the 1:1 reaction of [FeH(3)L(1)](BF(4))(2) or [MnH(3)L(1)](ClO(4))(2) with [CoL(1)]. [MH(3)L(1)][CoL(1)](X)(2) (M = Fe and X = BF(4) or M = Mn and X = ClO(4)), were characterized by IR, EA, variable temperature single crystal X-ray diffraction and Mössbauer spectroscopy in the iron case. The data support a spin crossover and high spin assignment for the iron(II) and manganese(II), respectively. DFT calculations demonstrate that the spin state of the iron(II) atom in {[FeH(3)L(1)][FeL(1)]}(2+) changes from high spin to low spin as the iron(II)-iron(III) distance decreases. This is supported by experimental results and is a result of hydrogen bonding interactions which cause a significant compression of the M(II)-N(pyrazole) bond distances.
authors.affiliation: The Catholic University, Washington, DC 20064, USA.
authors.forename: Cynthia T
authors.initials: CT
authors.lastname: Brewer
authors.forename: Greg
authors.initials: G
authors.lastname: Brewer
authors.forename: Ray J
authors.initials: RJ
authors.lastname: Butcher
authors.forename: Everett E
authors.initials: EE
authors.lastname: Carpenter
authors.forename: Ann M
authors.initials: AM
authors.lastname: Schmiedekamp
authors.forename: Carl
authors.initials: C
authors.lastname: Schmiedekamp
authors.forename: Alison
authors.initials: A
authors.lastname: Straka
authors.forename: Carol
authors.initials: C
authors.lastname: Viragh
authors.forename: Yevgeniy
authors.initials: Y
authors.lastname: Yuzefpolskiy
authors.forename: Peter
authors.initials: P
authors.lastname: Zavalij
mesh_terms: D000447:Aldehydes / Q000138:chemical synthesis / Q000737:chemistry; D003035:Cobalt / Q000737:chemistry*; D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry*; D005029:Ethylenediamines / Q000737:chemistry; D005290:Ferric Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D005296:Ferrous Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D006860:Hydrogen Bonding; D008345:Manganese / Q000737:chemistry*; D008958:Models, Molecular; D011720:Pyrazoles / Q000737:chemistry*; D011789:Quantum Theory; D012545:Schiff Bases / Q000138:chemical synthesis / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D015204:Spectroscopy, Mossbauer; D056928:X-Ray Absorption Spectroscopy
chemical_list: D000447:Aldehydes; D056831:Coordination Complexes; D005029:Ethylenediamines; D005290:Ferric Compounds; D005296:Ferrous Compounds; D011720:Pyrazoles; D012545:Schiff Bases; D003035:Cobalt; C099539:tris(2-aminoethyl)amine; D008345:Manganese