Eight new mono- and diphosphonates of cobalt(II), ACo(O3PPh)2⋅H2O (A = Ca(1), Sr(2)), BaCo(O3PPh)2·2H2O(3), ACo((O3PCH2Ph)2·2H2O (A = Sr(4), Ba(5), ACo(O3P(CH2)2PO3)⋅2H2O (A = Ca(6), Sr(7) and SrCo(O3P(CH2)3PO3)⋅2H2O(8), were isolated by hydrothermal method and structurally characterized by single crystal X-ray diffraction. They contain tetrahedrally coordinated Co2+ ion. The five phenyl- and benzylphosphonates, 1–5 have layered structures, wherein the cobalt and alkaline earth metal ions are ordered, confined approximately to a crystallographic plane and bonded to oxygen atoms of phenyl- or benzylphoshonate moieties and water of crystallization. The diphosphophonates 6–8 have pillared-layered structures and the magnetic susceptibilities of compounds 7 and 8 vary with temperature as per the Curie-Weiss law above 10 K. © 2018 Elsevier Inc.