Mössbauer spectra of some separately prepared samples of the complex polymer [Fe(bipy)ox1.1]n are recorded at 4.2 K. Magnetically split subspectra are observed. The different shape of one of these subspectra in the several samples can be explained by a decreasing electronic spin–spin relaxation frequency with decreasing concentration of the pertinent iron ion. The assumption of a slowly relaxing paramagnetism is supported by the behaviour of the magnetic susceptibility.