Twenty new molybdenum phosphonates and diphosphonates have been synthesized and structurally characterized by single crystal and powder X-ray diffraction, CHN analyses, spectroscopic and thermal studies. Four of them are molecular phenyl- and benzyl-phosphonates containing discrete [(MoO3)5(O3PR)2]4- (R = Ph or CH2Ph) cyclic anions. The sixteen non-molecular compounds are layered isostructural phenylphosphonates, A2[Mo2O5(O3PPh)2] (A = NH4, Tl, Rb, Cs) and K1.5(H3O)0.5[Mo2O5(O3PPh)2] and the corresponding diphosphonate compounds with pillared anionic layers, A2[Mo2O5(O3P(CH2)3PO3)], A2[Mo2O5(O3P(CH2)4PO3)] and A2[Mo2O5(O3P(C6H4)PO3)]. The A+ ions reside in the interlayer region as well as in the cavities within the anionic layers. © The Royal Society of Chemistry 2017.