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Related Concept Videos

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Coordination compounds and complexes exhibit different colors, geometries, and magnetic behavior, depending on the metal atom/ion and ligands from which they are composed. In an attempt to explain the bonding and structure of coordination complexes, Linus Pauling proposed the valence bond theory, or VBT, using the concepts of hybridization and the overlapping of the atomic orbitals. According to VBT, the central metal atom or ion (Lewis acid) hybridizes to provide empty orbitals of suitable...
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Two NMR-active nuclei bonded to a central atom can be involved in geminal or two-bond coupling. Geminal coupling is commonly seen between diastereotopic protons in chiral molecules and unsymmetrical alkenes, among others.
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Coupling interactions are strongest between NMR-active nuclei bonded to each other, where spin information can be transmitted directly through the pair of bonding electrons. While nuclei polarize their electrons to the opposite spins, the bonding electron pair has opposite spins. Configurations with antiparallel nuclear spins are expected to be lower in energy. When coupling makes antiparallel states more favorable, J is considered to have a positive value. The one-bond coupling constant, 1J,...
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Color in Coordination Complexes
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Isomerism in Complexes
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Spin Crossover in Fe(II) Complexes with N4S2 Coordination.

Alejandra Arroyave1, Anders Lennartson2, Alina Dragulescu-Andrasi1

  • 1Department of Chemistry and Biochemistry, Florida State University , 95 Chieftan Way, Tallahassee, Florida 32306, United States.

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Summary
This summary is machine-generated.

Iron complexes with a tetradentate ligand and coligands show temperature-induced spin crossover (SCO). Stronger ligand fields shift SCO to higher temperatures, with one complex exhibiting light-induced excited spin state trapping.

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Area of Science:

  • Coordination Chemistry
  • Materials Science
  • Physical Chemistry

Background:

  • Spin crossover (SCO) in iron(II) complexes is crucial for molecular switches and sensors.
  • Tuning SCO properties requires careful ligand design and exploration of coligands.
  • Understanding the influence of ligand field strength on SCO behavior is essential.

Purpose of the Study:

  • To synthesize and characterize novel mononuclear iron(II) complexes with a tetradentate ligand (bpte) and various monodentate coligands (NCS-, NCSe-, NCBH3-).
  • To investigate the temperature-induced spin crossover (SCO) properties of these complexes.
  • To explore the effect of ligand field strength and polymorphism on SCO behavior and light-induced effects.

Main Methods:

  • Synthesis of mononuclear iron(II) complexes: [Fe(bpte)(NCE)2] (E = S, Se, BH3).
  • Temperature-dependent magnetic susceptibility measurements to study spin crossover.
  • Mössbauer spectroscopy to analyze spin states and light-induced excited spin state trapping (LIESST).

Main Results:

  • Complexes 1, 2, and 3 exhibit temperature-induced SCO, with SCO temperature increasing with ligand field strength (NCS- < NCSe- < NCBH3-).
  • Complex 3 shows complete SCO at T1/2 = 243 K.
  • Polymorph α-2 of complex 3 displays a two-step SCO and cooling-rate-dependent residual high-spin fraction, with LIESST achieving up to 85% HS fraction at 4.2 K.

Conclusions:

  • The ligand field strength of coligands significantly influences the SCO transition temperature in Fe(II) complexes.
  • Polymorphism plays a critical role in the SCO behavior, leading to distinct transition profiles and residual spin states.
  • Light-induced excited spin state trapping (LIESST) is an effective method to induce and control spin states in these iron complexes.