学位論文要旨

Synthesis of Cu(hfac)2 Complexes with 3-Pyridyl-Substituted Nitroxide Radicals
and Study Their Physical Properties(3-ピリジル置換ニトロキシドラジカルを有するCu(hfac)2錯体の合成及び物性評価)
Tatiana Sherstobitova
Introduction
Copper(II) complexes with nitroxide radicals have recently attracted particular attention. Their magnetic
behavior strongly correlates with the geometry of the coordination Cu 2+ sphere, which is substantiallyaffected by the molecular structure of nitroxide ligand. The equatorial coordination of the nitroxyl group(NO group) results in the strong antiferromagnetic Cu2+-radical exchange coupling (J << 0), while the axial
binding leads to ferromagnetic exchange interactions (J > 0). In some cases, the energy gap between
equatorial and axial coordination is very weak that allows switching magnetic exchange interactions bychange of temperature, pressure or light irradiation.
CF3
Only a few numbers of the Cu(II) complexes with nitroxides exhibit structural- F3C
O O
magnetic anomalies under external stimuli. Even a minor modification of a ligand leadsCu
to significant change in molecular and crystal structures of the resulting complexes.
O OThat strongly affects the parameters of magnetic transitions as well as can be resulted in F3CCF3Cu(hfac)2
the assembly of phases that cannot exhibit any structural-magnetic anomalies. Cu(hfac)2(O)complexes with various derivatives of 3-pyridyl-substituted nitronyl and iminoRN
nitroxides (NN/ImN-3Py) are of special interest due to their diversity of molecularthspecies and magnetic properties. Introduction of Me group into the 4 position of theNNpyridine ring for NN-3Py ligand has led to the formation of Cu(hfac)2 complexes withOdifferent structures and magnetic behavior. The aim of performed research was theNN/ImN-3PyRndthth
R = Me, Br
study of the effect of substituents located in the 2 , 5 or 6 positions of the pyridine
heterocycle on the coordination ability of NN/ImN-3PyR ligands and structure and magnetic behavior of
the resulting Cu(hfac)2 complexes. Me and Br groups were chosen as substituents since both of them havethe same spatial size, but different electronic properties. Important tasks in the study of the physicalproperties of Cu(II)-nitroxide complexes included the investigation of the effect of pressure on themagnetic behavior of the selected complexes and the development of a method for measuring thetemperature dependence of the dielectric constant for materials undergoing magnetic anomalies.
Results and Discussion
1. Cu(hfac)2 complexes with Me- and Br-Substituted 3-Pyridyl Nitronyl Nitroxides
Reaction of Cu(hfac)2 with NN-3PyR (R = Me, Br) led to the assembly for the diverse set ofcoordination complexes: mononuclear [Cu(hfac)2NN-3Py2-Me], binuclear [{Cu(hfac)2}2(H2O)NN-3Py2-Me],trinuclear [{Cu(hfac)2}3(NN-3Py6-Br)2], pentanuclear [{Cu(hfac)2}5(NN-3Py2-Me)2] and [{Cu(hfac)2}5(NN3Py2-Me)4],cocrystals[Cu(hfac)2(NN-3Py2-Br)2]·[Cu(hfac)2(H2O)2]and[Cu(hfac)2(NN-3Py2Br)2]·2[Cu(hfac)2H2O], 1D polymers [Cu(hfac)2NN-3Py2-Br]n and [Cu(hfac)2NN-3Py6-Br]n, and cyclic
dimers [Cu(hfac)2NN-3Py5-Me]2, [Cu(hfac)2NN-3Py5-Br]2, and [Cu(hfac)2NN-3Py6-Me]2. Molecular
structures of obtained complexes are strongly affected by substituent type and its location in the pyridine
heterocycle. Occupation of the 2nd position of the pyridine ring increases the steric hindrance for both imine(NPy) and nitroxide coordination sites of NN-3Py2-R (R = Me, Br) that is favorable for the formation ofvarious conformers and precipitation of complexes with different molecular structures. Uniquepentanuclear [{Cu(hfac)2}5(NN-3Py2-Me)2] and [{Cu(hfac)2}5(NN-3Py2-Me)4] complexes have not prioranalogs and are valuable model objects for investigation of a mechanism for the formation of various
coordination polymers. The arrangement of long Cu-ONO bonds due to the weakening nitroxide donor sitein complexes based on NN-3Py2-R (R = Me, Br) ligands results in the ferromagnetic exchange interactionsin three-spin coupled {>N-•O-Cu2+-O•-N<} clusters. Complexes, where substituents do not considerably
affect the coordination ability of ligands (NN-3Py5-Me, NN-3Py5-Br, NN-3Py6-Me), exhibit strong
antiferromagnetic exchange interactions between spins of Cu2+ ion and nitroxide.

2. Cu(hfac)2 complexes with Me- and Br-Substituted 3-Pyridyl Imino Nitroxides
Introduction of Me and Br groups into the 2nd, 5th or 6th positions of the pyridine ring for ImN-3Py
resulted in obtaining of eight Cu(hfac)2 complexes: mononuclear [Cu(hfac)2ImN-3Py2-Br], trinuclear I[{Cu(hfac)2}3(ImN-3Py2-Me)2],II-[{Cu(hfac)2}3(ImN-3Py2-Me)2],[{Cu(hfac)2}3(ImN-3Py2-Br)2],
6-Me
6-Br
[{Cu(hfac)2}3(ImN-3Py )2], and [{Cu(hfac)2}3(ImN-3Py )2], and tetranuclear cyclic dimers[{Cu(hfac)2}2(ImN-3Py5-Me)]2, [{Cu(hfac)2}2(ImN-3-Py5-Br)]2. Location of substituents in the leaststerically hindered 5th position results in obtaining of tetranuclear [{Cu(hfac)2}4(ImN-3Py5-R)2] complexes,
where all three coordination sites of ImN-3Py5-R are coordinated by Cu2+. Steric hindrance for the 2nd and6th positions of the pyridine heterocycle essentially reduces donor ability for the N Py site and the NO group(up to the absence of coordination). Various crystal packing of trinuclear [{Cu(hfac)2}3(ImN-3PyR)2] (R =Me, Br) complexes causes the diversity of their magnetic behavior due to different intermolecular magneticexchange interactions. Occupation of the 2nd position by Me group or Br atom favorable both to theformation of several polymorphs and to the realization of phase transitions in solids associated withswitching of intermolecular magnetic exchange interactions (Figure 1). It was shown that application ofpressure ~0.56 GPa for II-[{Cu(hfac)2}3(ImN-3Py2-Me)2] results in stabilization of strongly-coupled state
between spins of nitroxide ligands in room temperature region (Figure 1a).
(a)(b)(c)Figure 1. Temperature dependences of MТ for (a) II-[{Cu(hfac)2}3(ImN-3Py2-Me)2] (■) – 10-4 GPa,() – 0.56 GPa and (b) [{Cu(hfac)2}3(ImN-3Py2-Br)2] (▲) and (c) structure of [{Cu(hfac)2}3(ImN-3Py2-Br)2].
3. Thermal Variation of Permittivity for Cu(hfac)2 Complexes with 3-Pyridyl Nitronyl Nitroxide
LigandTemperature variable dielectric measurements of the powdered polycrystalline pelleted sample for the[{Cu(hfac)2}4(NN-3Py)2] tetranuclear dimer complex (Figure 2a) reviled the gradual change of permittivity
in the temperature region of 40-120 K (Figure 2b). That is in agreement with the magnetic transition fromweakly ferromagnetic to strongly antiferromagnetic coupled states for [{Cu(hfac)2}4(NN-3Py)2].
(a)(b)

Figure 2. (a) Structure and (b) temperature dependences of permittivity at 316 kHz (■) and MТ for▲ – solid and ● – pelleted samples for [{Cu(hfac)2}4(NN-3Py)2].
Conclusion
Changing of electronic and steric properties for substituents allows
tuning the donor ability of coordination sites for the Me- and Brsubstituted NN/ImN-3PyR ligands. This can serve as a powerful tool forthe assembly of Cu(II) complexes with diverse molecular and crystal
structures and different magnetic behavior. The studied pressure effecton magnetic properties of obtained complexes and investigation ofpeculiarities for thermally induced switching of dielectric constant can give valuable information about thenature of driving force and mechanism of phase transitions in Cu(II)-nitroxide complexes that can be usefulfor creation of new types of electronic devices for pressure/temperature detection and for data storage.