Effective magnetic coupling with strong spin frustration in (Ph3MeP+)(C60•-) and reversible C60•- dimerization in (Ph3MeP+)(C60•-)•C6H5CN. Effect of solvent on structure and properties

Solvent free and solvent containing salts of the C-60(center dot-) radical anions with the triphenylmethylphosphonium cations, (Ph3MeP+)(C-60(center dot-)) (1) and (Ph3MeP+)(C-60(center dot-))center dot C6H5CN (2), have been obtained. The salts show different structures and physical properties. Complex 1 has double chains from C-60(center dot-) with triangular fullerene arrangement and short interfullerene center-to-center distances of 10.079(1)-10.103(1) angstrom. No dimerization is observed in 1 preserving unpaired spins down to 1.9 K and providing magnetic moment of 1.68 mu(B) at 300 K. Weiss temperature of Theta = -60 K indicates a strong antiferromagnetic coupling of spins. In spite of that, no magnetic ordering is observed down to 1.9 K showing that 1 has strong frustration of spins (f = Theta/T-N > 30) due to triangular fullerene lattice. Compound 2 additionally contains the C6H5CN solvent molecules and has a layered structure with fullerene hexagons accommodating the Ph3MeP+ cations and C6H5CN solvent molecules in the center. Interfullerene center-to-center distances vary in the fullerene layers in the 9.921(2)-10.066(2) angstrom range. Fullerenes dimerize reversibly in pairs with a shortest interfullerene center-to-center distance of 9.921(2) angstrom below 220 K to form diamagnetic singly-bonded (C-60(-))(2) dimers.