Abstract
A series of new bis(pyrazol-3-yl)pyridines (LR) N,N′-disubstituted by 4-functionalized 2,6-dibromophenyl groups have been synthesized to study the effect of a distal substituent on the spin-crossover (SCO) behaviour of the iron(II) complexes [Fe(LR)2](ClO4)2 by variable-temperature magnetometry, NMR spectroscopy, and X-ray diffraction. The SCO-assisting tendency of the substituents with different electronic and steric properties (i.e., the bromine atom and the methyl group) in the para-position of the 2,6-dibromophenyl group is discussed. Together with earlier reported SCO-active iron(II) complexes with N,N′-disubstituted bis(pyrazol-3-yl)pyridines, these new complexes open the way for this family of SCO compounds to emerge as an effective ‘tool’ in revealing structure–function relations, a prerequisite for successful molecular design of switchable materials for future breakthrough applications in sensing, switching, and memory devices.
Highlights
IntroductionMetal complexes or frameworks [1] with the transition metal ions able to reversibly switch between low-spin (LS) and high-spin (HS) electronic configurations as a response to an applied stimulus (such as temperature, pressure, light irradiation, or electric or magnetic field [1]) are promising candidates to be incorporated into various materials and devices [2,3]
Metal complexes or frameworks [1] with the transition metal ions able to reversibly switch between low-spin (LS) and high-spin (HS) electronic configurations as a response to an applied stimulus are promising candidates to be incorporated into various materials and devices [2,3]
N,N -disubstituted by 4-functionalized 2,6-dibromophenyl groups allowed for probing
Summary
Metal complexes or frameworks [1] with the transition metal ions able to reversibly switch between low-spin (LS) and high-spin (HS) electronic configurations as a response to an applied stimulus (such as temperature, pressure, light irradiation, or electric or magnetic field [1]) are promising candidates to be incorporated into various materials and devices [2,3] This ability for a spin-crossover (SCO) between the two configurations with different optical, magnetic, electrical and mechanical properties is exploited in displays [4], switches [5], sensors [6], memory devices [7], thermometers [8], and contrast agents [9] in magnetic resonance imaging [2,3]. Crystals 2021, 11, 922 stabilize the HS state of the metal ion through the steric demand that makes its LS state more unlikely, less straightforward role the for other, more remote stabilize the HSwith statea of the metal ion through steric demand that substituents makes its LS[12]
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