<p>Crystallization of Strandberg-type cluster (STC) based solids using 3-aminopyridine (3-<i>ampy</i>) viz<i>.</i> {3-H<i>ampy</i>}₄[{PO₃(OH)}₂Mo₅O₁₅]·H₂O (<b>1</b>) and {3-H<i>ampy</i>}₁₀[{PO₃(OH)}{PO₄}Mo₅O₁₅]₂·4H₂O (<b>2</b>) was achieved in aqueous solution under acidic conditions. While, strong hydrogen bonding interactions between protonated 3-aminopyridine moieties and STC dictated the crystal packing of the solids, non-bonding interactions such as C–H···π and π···π interactions strengthened the crystal structure. Detailed crystal structure analysis of <b>1</b> and<b> 2</b> demonstrated that both form 2-D supramolecular assemblies having voids occupied by protonated 3-aminopyridine moieties and lattice water molecules. Interestingly, pH and temperature influenced the occurrence of different ligand: cluster ratio in the solids. The results also suggested that solids <b>1</b> and<b> 2</b> were stable over a wide range of temperature indicating the formation of thermodynamically stable phases. Optical band gap energy calculations indicated that <b>1</b> showed lower band gap energy than <b>2</b> owing to greater extent of protonation of the Strandberg-type cluster.</p> Graphical abstract <p></p>