The coordination polymers [Sr(Hpcp)2(H2O)]n, 1, and [Ba(Hpcp)2(H2O)]n, 2, (H2pcp = p,p′-diphenylmethylenediphosphinic acid) are isomorphous and consist of 1D chains. The solid compounds were characterized by X-ray diffraction, solid state NMR spectroscopy and thermogravimetric analysis. The photophysical properties of 1 and 2 were also investigated. The refinement of the crystal structures was based on laboratory X-ray powder diffraction data using the Rietveld method. An analysis of the effect of the size of the alkaline earth cation on the network dimensionality was based on a series of coordination polymers bearing ligands comparable to pcp in shape. We found that, as expected, the size of the metal atoms has a minor role in determining the dimensionality of the network, whereas other factors such as steric requirements of the ancillary groups bonded to the phosphorus atoms or the strong tendency of this type of ligand to chelate metal atoms revealed to be important.