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Bipyrimidine-Bridged Dinuclear Iron(II) Spin Crossover Compounds

  • Chapter
Spin Crossover in Transition Metal Compounds I

Part of the book series: Topics in Current Chemistry ((TOPCURRCHEM,volume 233))

Abstract

This review reports on the study of the interplay between magnetic coupling and spin transition in 2,2′-bipyrimidine (bpym)-bridged iron(II) dinuclear compounds. The coexistence of both phenomena has been observed in {[Fe(bpym)(NCS)2]2(bpym)}, {[Fe(bpym)(NCSe)2]2(bpym)} and {[Fe(bt)(NCS)2]2(bpym)} (bpym=2,2′-bipyrimidine, bt=2,2′-bithiazoline) by the action of external physical perturbations such as heat, pressure or electromagnetic radiation. The competition between magnetic exchange and spin crossover has been studied in {[Fe(bpym)(NCS)2]2(bpym)} at 0.63 GPa. LIESST experiments carried out on {[Fe(bpym)(NCSe)2]2(bpym)}and {[Fe(bt)(NCS)2]2(bpym)}at 4.2 K have shown that it is possible to generate dinuclear molecules with different spin states in this class of compounds. A special feature of the spin crossover process in the dinuclear compounds studied so far is the plateau in the spin transition curve. Up to now, it has not been possible to explore with a microscopic physical method the nature of the species which constitute such a plateau, due to the relatively high temperatures at which the transition takes place. A two-step spin transition has been observed for {[Fe(phdia)2(NCS)2]2(phdia)} (phdia: 4,7-phenanthroline-5,6-diamine) with T 1/2(1) and T 1/2(2) located at 108 and 80 K, respectively. Due to this low temperature transition we were able to thermally trap, at liquid helium temperatures, the species present in the plateau of the spin transition curve. The results have revealed that the plateau consists mainly of [HS−LS] pairs, and they confirmed the hypothesis formulated earlier that the spin conversion in dinuclear entities proceeds via [HS−HS]↔[HS−LS]↔[LS−LS] pairs.

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Abbreviations

ST:

Spin transition

SCO:

Spin crossover

HS:

High spin

LS:

Low spin

χ M :

Molar magnetic susceptibility

T :

Temperature

T 1/2 :

Temperature at which 50 per cent of the “SCO-active” molecules have changed the spin state

T p :

Temperature at which the plateau of a two-step spin transition is centred

P :

Pressure

P 1/2 :

Pressure at which 50 per cent of the “SCO-active” molecules have changed the spin state

γ HS :

HS molar fraction

γHS(T):

HS molar fraction as a function of temperature

M :

Magnetisation

H :

Magnetic field

J :

Magnetic coupling parameter

D :

Zero field splitting parameter

g :

Landé factor

H ext :

External magnetic field

H eff :

Effective magnetic field

S :

Spin quantum number

#lt;S#gt;:

Average spin value

δ HS :

Isomeric shift value for the HS state

δ LS :

Isomeric shift value for the LS state

ΔE Q(HS) :

Quadrupole splitting for the HS state

ΔE Q(LS) :

Quadrupole splitting for the LS state

λ :

Light wavelength

ΔH :

Enthalpy difference between the HS and LS states

W :

Energetic stabilization of the [HS−LS] pair relative to the enthalpy average of the [HS−HS] and [LS−LS] states (ΔH/2)

Γ :

Parameter that accounts for the intermolecular interactions

bpym:

2,2′-bipyrimidine

bt:

2,2′-bithiazoline

phen:

1,10-phenanthroline

bipy:

2,2′-bipyridine

phdia:

4,7-phenanthroline-5,6-diamine

pic:

2-picolylamine

ptz:

1-propyltetrazole

py:

pyridine

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Acknowledgement

We thank the Ministerio Español de Ciencia y Tecnología (project BQU 2001-2928) for financial assistance. We also thank the European Commission for granting the TMR-Network “Thermal and Optical Switching of Molecular Spin States (TOSS)”, Contract No. ERB-FMRX-CT98-0199EEC/TMR. The financial help from the DFG, the Fonds der Chemischen Industrie and the Materialwissenschaftliches Forschungszentrum of the University of Mainz is also gratefully acknowledged. A. B. G. is grateful for a fellowship from the Alexander von Humboldt Foundation.

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Authors and Affiliations

  1. Departament de Química Inorgánica/Institut de Ciència Molecular, Universitat de València, Doctor Moliner 50, Burjassot, València, Spain

    José Antonio Real & Ana B. Gaspar

  2. Departament de Física Aplicada, Universitat Politècnica de València, Camino de Vera s/n, 46071, València, Spain

    M. Carmen Muñoz

  3. Institut für Anorganische und Analytische Chemie, Johannes Gutenberg Universität, Staudinger Weg 9, 55099, Mainz, Germany

    Philipp Gütlich, Vadim Ksenofontov & Hartmut Spiering

Authors
  1. José Antonio Real
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  2. Ana B. Gaspar
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  3. M. Carmen Muñoz
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  4. Philipp Gütlich
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  5. Vadim Ksenofontov
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  6. Hartmut Spiering
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Correspondence to José Antonio Real or Philipp Gütlich .

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P. Gütlich H.A. Goodwin

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Real, J.A., Gaspar, A.B., Muñoz, M.C., Gütlich, P., Ksenofontov, V., Spiering, H. Bipyrimidine-Bridged Dinuclear Iron(II) Spin Crossover Compounds. In: Gütlich, P., Goodwin, H. (eds) Spin Crossover in Transition Metal Compounds I. Topics in Current Chemistry, vol 233. Springer, Berlin, Heidelberg. https://doi.org/10.1007/b13534

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  • DOI: https://doi.org/10.1007/b13534

  • Publisher Name: Springer, Berlin, Heidelberg

  • Print ISBN: 978-3-540-40394-4

  • Online ISBN: 978-3-540-44981-2

  • eBook Packages: Springer Book Archive

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