NMR evidence for 1D antiferromagnetic properties in Cs1C60 and Rb1C60 polymers

Structure, optical, and magnetic properties of (PPN+)2(C70(2-))⋅2 C6H4Cl2, which contains dianionic polymeric (C70(2-))n chains

A new salt, (PPN(+))2(C70(2-))⋅2 C6H4Cl2 (1), which contains C70(2-) dianions, has been obtained as single crystals (PPN(+) = bis(triphenylphosphine)iminium cation). The C70(2-) dianions form polymeric zigzag (C70(2-))n chains, in which the fullerene units are bonded through single C-C bonds of length 1.581(5)-1.586(6) Å. The distance between the centers of neighboring C70(2-) units is 10.441 Å. The optical and magnetic properties of (C70(2-))n have also been studied. Decreasing the symmetry of C70 in the polymer activate about 20 new IR bands in addition to the 10 IR-active bands of the starting C70. The polymeric structure shows absorptions in the visible and NIR regions, with three main bands at 890, 1200, and 1550 nm, instead of one band of isolated C70(2-) dianions at 1165-1184 nm. We concluded that the (C70(2-))n polymer was diamagnetic, with a negative molar magnetic susceptibility of -3.82×10(-4)  emu  mol(-1) per C70(2-) dianion. The polymer is EPR silent and a weak narrow EPR signal in salt 1 is due to impurities, which only constitute 0.84% of spin S = 1/2 of the total amount of fullerene C70.

Metal-insulator and structural phase transition observed by ESR spectroscopy and x-ray diffraction in KC60

We have performed electron spin resonance (ESR) spectroscopy and x-ray diffraction experiments at low temperature on KC60 single crystals. ESR data reveal the occurrence of a metal-insulator phase transition at about 50 K. In the same temperature range, we observe the stabilization of a superstructure which doubles the volume of the unit cell. We suggest that displacements of the K atoms and a modulation of the C60 charge may be involved in the mechanism of this phase transition. These results shed new light on the subtle interplay of structure, dimensionality, and electronic properties in the AC60 fullerides.

Electron spin density distribution in the polymer phase of CsC60: assignment of the NMR spectrum

We present high resolution 133Cs-13C double resonance NMR data and 13C-13C NMR correlation spectra of 13C enriched samples of the polymeric phase of CsC60. These data lead to a partial assignment of the lines in the 13C NMR spectrum of CsC60 to the carbon positions on the C60 molecule. A plausible completion of the assignment can be made on the basis of an ab initio calculation. The data support the view that the conduction electron density is concentrated at the C60 "equator," away from the interfullerene bonds.