Structural insight into the cooperativity of spin crossover compounds

Acta Crystallographica Section B Structural Science Crystal Engineering and Materials, vol. 79, pp. 354–367

Abstract

Spin-crossover (SCO) compounds are promising materials for a wide variety of industrial applications. However, the fundamental understanding of their nature of transition and its effect on the physical properties are still being fervently explored; the microscopic knowledge of their transition is essential for tailoring their properties. Here an attempt is made to correlate the changes in macroscopic physical properties with microscopic structural changes in the orthorhombic and monoclinic polymorphs of the SCO compound Fe(PM-Bia) 2 (NCS) 2 (PM = N -2′-pyridylmethylene and Bia = 4-aminobiphenyl) by employing single-crystal X-ray diffraction, magnetization and DSC measurements. The dependence of macroscopic properties on cooperativity, highlighting the role of hydrogen bonding, π–π and van der Waals interactions is discussed. Values of entropy, enthalpy and cooperativity are calculated numerically based on the Slichter–Drickamer model. The particle size dependence of the magnetic properties is probed along with the thermal exchange and the kinetic behavior of the two polymorphs based on the dependence of magnetization on temperature scan rate and a theoretical model is proposed for the calculation of the non-equilibrium spin-phase fraction. Also a scan-rate-dependent two-step behavior observed for the orthorhombic polymorph, which is absent for the monoclinic polymorph, is reported. Moreover, it is found that the radiation dose from synchrotron radiation affects the spin-crossover process and shifts the transition region to lower temperatures, implying that the spin crossover can be tuned with radiation damage.

Authors 11

1. Hend Shahed Aachen Institute of Crystallography

   Forschungszentrum Jülich · RWTH Aachen University

   Affiliation as printed

   Institute of Crystallography, RWTH Aachen University, Jägerstr. 17-19, 52066 Aachen, Germany

   Jülich Centre for Neutron Science (JCNS-2) and Peter Grünberg Institute (PGI-4), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany

2. Manuel Angst

   Forschungszentrum Jülich

   Affiliation as printed

   Jülich Centre for Neutron Science (JCNS-2) and Peter Grünberg Institute (PGI-4), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany

3. Jörg Voigt

   Forschungszentrum Jülich

   Affiliation as printed

   Jülich Centre for Neutron Science (JCNS-2) and Peter Grünberg Institute (PGI-4), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany

4. J. Perßon

   Forschungszentrum Jülich

   Affiliation as printed

   Jülich Centre for Neutron Science (JCNS-2) and Peter Grünberg Institute (PGI-4), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany

5. Karl Wilhelm Törnroos

   University of Bergen

   Affiliation as printed

   Department of Chemistry, University of Bergen, Allégaten 41, N-5007 Bergen, Norway

6. Dmitry Chernyshov

   European Synchrotron Radiation Facility

   Affiliation as printed

   Swiss-Norwegian Beamlines at the European Synchrotron Radiation Facility, 38000 Grenoble, France

   Swiss–Norwegian Beamlines at the European Synchrotron Radiation Facility, 38000 Grenoble, France

7. H. Gildenast Aachen Institute of Inorganic Chemistry

   RWTH Aachen University

   Affiliation as printed

   Institute of Inorganic Chemistry, RWTH Aachen University, 52074 Aachen, Germany

8. Michael Ohl

   Forschungszentrum Jülich · University of Tennessee at Knoxville

   Affiliation as printed

   Jülich Centre for Neutron Science (JCNS-1), Forschungszentrum Jülich, 52425 Jülich, Germany

   Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA

9. G. Saffarini

   An-Najah National University

   Affiliation as printed

   Physics Department, An-Najah National University, Nablus, Palestine

10. Andrzej Grzechnik Aachen Institute of Crystallography

    Forschungszentrum Jülich · RWTH Aachen University

    Affiliation as printed

    Institute of Crystallography, RWTH Aachen University, Jägerstr. 17-19, 52066 Aachen, Germany

    Jülich Centre for Neutron Science (JCNS-4), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany

11. Karen Friese Aachen Institute of Crystallography

    Forschungszentrum Jülich · RWTH Aachen University

    Affiliation as printed

    Jülich Centre for Neutron Science (JCNS-2) and Peter Grünberg Institute (PGI-4), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany

    Institute of Crystallography, RWTH Aachen University, Jägerstr. 17-19, 52066 Aachen, Germany