Spin Glass‐like Behavior of Poly(phenylacetylene) Prepared with a Rh Complex Catalyst, 1

Abstract

Summary: Magnetic field dependence of poly(phenylacetylene) (PPA) that has been stereoregularly prepared with a Rh complex catalyst was investigated in detail between 2 K and 300 K. The data showed a spin glass‐like magnetic behavior, i.e., two cusps were clearly observed when PPA was zero‐field‐cooled together with slow increasing of the magnetization (called an ageing effect) at 45 K. The observed spin glass‐like behavior has been discussed in terms of an ageing effect, which may have been caused by weak anti‐ferromagnetic interactions between intra‐ and/or inter‐magnetic spins produced by cis‐to‐trans isomerization through the rotational scission of the cis CC bond of the PPA polymer during polymerization.Intra‐molecular anti‐ferromagnetic interactions.magnified imageIntra‐molecular anti‐ferromagnetic interactions.

Unique Superparamagnetic‐like Behavior Observed in Non‐π‐delocalized Nitroxide Diradical Compounds Showing Discotic Liquid Crystalline Phase

“…In this context, 1 (80:20) composed of a 80:20 mixture of ( R , S )‐ 1 and ( R *, R *)‐ 1 displayed an extraordinarily larger χ M or χ TIM than 1 (95:5) did. These results are consistent with the formation of magnetically inhomogeneous domains with intermolecular short contacts in the solid phase and their enlargement in the LC phase under low magnetic fields, which is reminiscent of the magnetic properties of spin glass materials induced by thermal processing or the presence of impurity . Such an existence of a large χ TIM component in the original nanocrystalline solid I of compounds 1 with a large molecular structure was not observed in the original crystalline phases of small nitroxide radical compounds showing rod‐like LC phases .…”

“…These results proved almost negligible contamination of extrinsic magnetic metal or metal ion impurities in ( R , S )‐ 1 and ( R *, R *)‐ 1 and provided the first observation of an increase in magnetic interactions only by thermal processing for ( R , S )‐ 1 . Such a thermal phenomenon was observed in the metallic spin glass materials and spin glass‐like poly(phenylacetylene) π‐radicals …”

“…These results proved almostn egligible contamination of extrinsic magnetic metal or metal ion impurities in (R,S)-1 and (R*,R*)-1 and provided the first observation of an increasei nm agnetic interactions only by thermalp rocessing for (R,S)-1.S uch at hermal phenomenon was observed in the metallics pin glass materials [38,39] and spin glass-likep oly(phenylacetylene) p-radicals. [40] Furthermore,i tw as confirmed that so long as compounds 1 composed of the major (R,S)-1 and minor (R*,R*)-1 components were used, (1) the occurrence of the superparamagnetic-like MÀH behavior in the solids Ia nd II and( 2) the large c M increase at the solidI -to-Col h phase transition in the first heating run were fully reproducible. In this instance, the c TIM values in the solid Ii nt he first heating run and in the solid II in the first cooling run varied, depending on the ratio of the two components.…”

“…From these experimentalr esults, the following five facts were revealed;( 1) neither pure (R,S)-1 nor (R*,R*)-1 exhibited a superparamagnetic-like behaviori nt he originals olid phase in the first heating run, (2) pure (R,S)-1 showedt he superparamagnetic-like MÀH behavior only by the first cooling from the isotropic phase at 0.05 T, most likely due to the partial formation of boat and/orh alf-chair conformers of (R,S)-1 which are assumed to result from the thermalm otion of the cyclohexane ring in the isotropic phase and serve as necessary impurities to lead to the partial formation of magnetically inhomogeneous domains, (3) the original solid Ic omposed of major (R,S)-1 and minor (R*,R*)-1 showedt he superparamagnetic-like behavior most likely because (R*,R*)-1 served as an organic impurity to form magnetically inhomogeneous domains easily,( 4) such a superparamagnetic-like MÀH behavior was not caused by either externalm agnetic impurities such as iron and nickel or the smallm olecular Dc,a nd (5) such au nique magnetic phenomenon is reminiscent of the magnetic properties of spin glass materials induced by thermalp rocessing [38][39][40] or the presence of impurity. [39,41] To gain am icroscopic insighti nto the mechanism of the observed positive magneto-LC effect operating in the Col h phase of 1(95:5), the temperature dependences of EPR g-value and peak-to-peak line width (DH pp )w ere compared with that of the c M (Figure 10 a,b).…”

RhI-complexes of ditopic bis(pyrazol-1-yl)borate ligands: Assessment of their catalytic activity towards phenylacetylene polymerization

“…To identify promising applications of ditopic scorpionates of the general formula ½1; 4-ðBðR 0 Þpz R 2 Þ-C 6 H 4 -ðBðR 0 Þpz R 2 Þ 2À (pz R : 3-substituted pyrazolide) in homogeneous catalysis we chose to investigate the Rh-mediated polymerization of phenylacetylene, because (i) mononuclear complexes ½ðHBðR 0 Þpz R;R 2 ÞRhðcodÞ (cod: cyclooctadiene) reveal a high activity in this reaction [26], (ii) some benefit of two cooperating metal centers has already been confirmed for homogeneous olefin polymerization [27][28][29][30][31], and (iii) stereoregular poly(phenylacetylene) derivatives possess interesting and useful optoelectronic properties [32][33][34][35][36][37][38].…”