Optical absorption spectra, magnetic susceptibility and magnetization of nickelates R 2BaNiO 5 (R=Nd-Gd, Dy-Tm) containing isolated NONi chains have been measured. Magnetic ordering temperatures were found to be considerably higher than the temperatures of the maxima in the magnetic susceptibility. Most of the compounds R 2BaNiO 5 exhibit two metamagnetic transitions. By comparison with neutron diffraction data for Er 2BaCuO 5 it was shown that the interaction R-Ni dominates and that the magnetic behavior of the rare earth subsystem can be satisfactorily described in a molecular-field framework.