Magnetic measurements of the quasi I-D molecular magnet formed by the coordination polymer of purely organic alpha-nitronyl nitroxide radical and manganese(II) ions, namely [(R)-3MLNN-Mn(hfac)(2)], have been carried out under pressure up to 10 kbar at low temperatures. The results obtained show that the temperature of 3-D ferromagnetic ordering of the 1-D ferrimagnetic chains in this molecular magnet increases substantially under pressure. Analysis of the experimental data obtained, as well as a review of the ferromagnetic ordering temperature with respect to interchain coupling distances in closely related compounds, gives one grounds to suggest that the interchain magnetic coupling in the 3-D ferromagnetic ordering for this series of coordination complexes cannot be only dipolar (as often inferred). Rather, the interaction must be stronger, and in all likelihood, it is mediated mainly by exchange interactions.