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Publication Details
AFRICAN RESEARCH NEXUS
SHINING A SPOTLIGHT ON AFRICAN RESEARCH
chemistry
Thermally induced two-step, two-site incomplete
6
A
1
↔
2
T
2
crossover in a mononuclear iron(III) phenolate-pyridyl Schiff-base complex: A rare crystallographic observation of the coexistence of pure S = 5/2 and 1/2 metal centers in the asymmetric unit
Inorganic Chemistry, Volume 46, No. 23, Year 2007
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Description
The six-coordinate mononuclear iron(III) complexes [Fe(salpm) 2]ClO4·0.5EtOH, [Fe(salpm)2]Cl, [Fe{(3,5-tBu2)-salpm}2]X (X = ClO 4- or Cl-), and [Fe{(3,5-tBu 2)-salpm}2]NO3·2H2O [Hsalpm = N-(pyridin-2-ylmethyl)-salicylideneamine; H(3,5-tBu 2)-salpm = N-(pyridin-2-ylmethyl)-3,5-di-tert-butylsalicylideneamine] have been synthesized and isolated in crystalline form; their chemical identities have been ascertained by elemental analyses, FAB mass spectrometry, and infrared spectroscopy. The room-temperature effective magnetic moments [(8χMT)1/2 ∼ 5.85-5.90 μB] of these complexes are consistent with the high-spin (S = 5/2) ground state. These complexes are intensely colored on account of the strong pπ → dπ* LMCT visible absorptions. Definitive evidence for the structures of [Fe(salpm)2]ClO4·0.5EtOH and [Fe{(3,5-tBu2)-salpm}2]NO3· 2H2O has been provided by single-crystal X-ray crystallography. The monomeric complex cations in both compounds comprise two uninegative phenolate-pyridyl tridentate Schiff-base ligands coordinated meridionally to the iron(III) to afford a distorted octahedral geometry with a trans,cis,cis- [FeO2N4] core. Whereas [Fe(salpm)2]ClO 4·0.5EtOH undergoes a thermally induced 6A 1 ↔ 2T2 crossover, [Fe{(3,5- tBu2)-salpm}2]NO3·2H 2O retains its spin state in the solid state down to 5 K. However, EPR spectroscopy reveals that the latter complex does exhibit a spin transformation in solution, albeit to a much lesser extent than does the former. The spin crossover in [Fe(salpm)2]ClO4·0.5EtOH has resulted in an unprecedented crystallographic observation of the coexistence of high-spin and tow-spin iron(III) complex cations in equal proportions around 100 K. At room temperature, the two crystallographically distinct ferric centers are both high spin; however, one [Fe(salpm)2]+ complex cation undergoes a complete spin transition over the temperature range ∼200-100 K, whereas the other converts very nearly completely between 100 and 65 K; ∼10% of the complex cations in [Fe(salpm)2]ClO 4·0.5EtOH remain in the high-spin state down to 5 K. © 2007 American Chemical Society.
Authors & Co-Authors
Shongwe, Musa S.
Oman, Muscat
Sultan Qaboos University
Al-Rashdi, Badria A.
Oman, Muscat
Sultan Qaboos University
Adams, Harry
United Kingdom, Sheffield
The University of Sheffield
Morris, Michael J.
United Kingdom, Sheffield
The University of Sheffield
Mikuriya, Masahiro
Japan, Nishinomiya
Kwansei Gakuin University
Hearne, Giovanni R.
South Africa, Johannesburg
University of the Witwatersrand
Statistics
Citations: 59
Authors: 6
Affiliations: 4
Identifiers
Doi:
10.1021/ic700397u
ISSN:
00201669