A nonperturbative effect of phonons interacting with a chain of localized spins is discussed, in which singlet spin-phonon complexes arise. Depending on the coupling strength they can either involve all the spins (and form a nonmagnetic "crystal"), or screen them only partly (and form a weakly magnetic liquid mixture of mobile singlet complexes and unscreened spins). This purely quantum effect vanishes for classic spins. Average displacements are absent in both crystal and liquid phases, only zero vibrations are modulated. Generalizations for high D and applications to heavy fermions are discussed.