Reactions of (4-amino-1-hydroxybutylidine)-1,1-bisphosphonic acid (alendronic acid = LH 5 ) with one equivalent of the group 1 metal bases KOH, KHCO 3 , Rb 2 CO 3 , RbOH or Cs 2 CO 3 in aqueous solution at pH 4-5 gave the corresponding complexes [M(LH 4 )(H 2 O) n ].m(H 2 O), M = K (1), Rb (2) or Cs (3). Crystallisation of the products under varying conditions yielded differing hydrates and/or polymorphic phases. Rapid crystallisation of the potassium complex 1 from water/EtOH or water/DMSO gave 2[K(LH 4 )].3(H 2 O) (1a) whereas slow crystallisation from water or water/DMSO gave [K 2 (LH 4 ) 2 (H 2 O) 2 ].2H 2 O (1b phase I). For the rubidium complex 2, rapid crystallisation from water/EtOH gave the analogous [Rb 2 (LH 4 ) 2 (H 2 O) 2 ].2H 2 O (2b phase I) whereas slow crystallisation from water/DMSO also gave 2b, but as a mixture of phase I and the structural polymorph [Rb(LH 4 )(H 2 O)].H 2 O (2b phase II). In contrast, only [Cs(LH 4 )(H 2 O)].H 2 O (3b phase II) was obtained for the caesium complex 3 under all crystallisation conditions. A second complex type [M(LH 4 )(LH 5 )].2H 2 O (M = Rb 4, Cs 5), incorporating an additional coordinated alendronic acid molecule was also observed for the larger metals Rb and Cs as a minor product in some syntheses and isolated by fractional crystallisation for 4, but as the sole product from Cs(O 2 CH) and LH 5 for 5. The crystal structures of the complexes [M(LH 4 )(H 2 O) n ].m(H 2 O) 1a, 2b (phase II) and 3b (phase II) comprise edge-shared or corner-shared polyhedral chains that are linked by bridging bisphosphonate ligands into 2-D sheets. The 4-ammoniobutylidene chains protrude above and below the coordination layers and interact with neighbouring layers through hydrogen bonding of the terminal ammonium group forming distinctive supramolecular 3-D arrays. The phase I structure of 1b and 2b comprises ribbons of parallel M 4 (LH 4 ) 4 (H 2 O) 4 subunits arranged in a more close packed 3-D supramolecular network. For [M(LH 4 )(LH 5 )].2H 2 O (M = Rb 4, Cs 5), isolated M + cations, bridged by bisphosphonate ligands, are arranged into 2-D sheets, with the pendant 4-ammoniumbutylidene chains resulting in a 3-D lamellar network similar to those of 1a and 2b/3b (phase II). All of the [M(LH 4 )(H 2 O) n ].m(H 2 O) and [M(LH 4 )(LH 5 )].2H 2 O structures display strong PO-H…O(phosphonate) and N-H…O(phosphonate/water) hydrogen bond motifs which significantly impact upon the observed structures. Reactions of LH 5 with two equivalents of the group 1 metal bases MOH (M = Na, K, Rb, Cs) at pH 9-10 gave the di-metallated complexes [M 2 (LH 3 )(H 2 O) n ].(H 2 O) m (M = Na 6, K 7, Rb 8, Cs 9). Crystallisation of 6 from water/MeOH gave [Na 2 (LH 3 )(H 2 O) 4 ].H 2 O (6a) as a single phase. For 7, crystallisation from water/MeOH gave K 2 (LH 3 ).3(H 2 O) (7a) as the bulk product, whereas crystals of [K 2 (LH 3 )(H 2 O) 6 ] (7b) were grown from water/DMSO solutions. On standing, the crystals of 7b were converted into the bulk product 7a. The structures of 6a and 7b are chain rather than ...