  Recently, Arcon et al. reported ESR studies of the polymer phase (PP) of
Na_{2}Rb_{0.3}Cs_{0.7}C_{60} fulleride. It was claimed that this phase is a
quasi-one-dimensional metal above 45 K with a spin-gap below this temperature
and has antiferromagnetic(AF) order below 15 K, that is evidenced by
antiferromagnetic resonance(AFMR). For the understanding of the rich physics of
fullerides it is important to identify the different ground states. ESR has
proven to be a useful technique for this purpose. However, since it is a very
sensitive probe, it can detect a multitude of spin species and it is not
straightforward to identify their origin, especially in a system like
Na_{2}Rb_{x}Cs_{1-x}C_{60} with three dopants, when one part of the sample
polymerizes but the majority does not. The observation of a low dimensional
instability in the single bonded PP would be a novel and important result.
Nevertheless, in this Comment we argue that Na_{2}Rb_{0.3}Cs_{0.7}C_{60} is not
a good choice for this purpose since, as we show, the samples used by Arcon et
al. are inhomogeneous. We point out that recent results on the PP of
Na_{2}CsC_{60} contradicts the observation of low dimensional instabilities in
Na_{2}Rb_{0.3}Cs_{0.7}C_{60}.
