Anion binding is now an attractive area of investigation in the construction of supramolecular donor-acceptor complexes and in recent years more research has been devoted to employing the main principles of anion binding into practical applications such as anion sensors, catalysis, extraction of anions from mixtures, and medicinal use of transmembrane anion transport. Among various anion receptors, ammonium-based ones such as hexamminecobalt(III) [Co(NH3)6]3+ exhibits high binding affinity and selectivity [1-3] as well as a great potential as a broad-spectrum antiviral and antibacterial drug. We have used the receptor [Co(NH3)6]Cl3 in the reaction with different N,O-donor ligands to fabricate a new series of hydrogen-bonded complexes, namely [Co(NH3)6]Cl3•2(phen)•3(H2O) (1), [Co(NH3)6](Hbdc)(bdc)•3H2O (2), [Co(NH3)6]Cl2(Hpht)•2.5(H2O) (3), and [Co(NH3)6]11[Co(pdc)3]8(OH)•84(H2O) (4), where phen = 1,10′-phenanthroline, H2bdc = biphenyl-4,4′-dicarboxylic acid; H2pht = o-phthalic acid; H2pdc = 2,5-pyridinedicarboxylic acid. All complexes have been prepared from water or water/methanol solution and have been characterized by X-ray single crystal diffraction measurements. Compounds 1 and 2 crystallize in the triclinic space group P-1, 3 in the monoclinic space group I2/m, and 4 in the trigonal space group R-3, respectively. In these compounds CoIII centers are six-coordinated by NH3 molecules, forming a [Co(NH3)6]3+ octahedron, with CoN bond distances of 1.939(3) – 1.99(1) Å. In 4, the [CoII(pdc)3]4 anion (Fig. 1), has a distorted octahedral environment of the CoII center formed by three O atoms and three N atoms from three pdc2 residues with CoO bond distances in the range 2.079(2) – 2.093(28) Å and CoN bond distances of 2.131(3) – 2.140(3) Å. Multiple NHO, NHN, NHCl, OHCl and OHO hydrogen bonds (Fig. 2) which link the cations, anions and water molecules into a H-bonded network will be discussed.figureFig. 1. Structure of [CoII(pdc)3]4 anion in 4. Fig. 2. Fragment of crystal structure of 1.