Two new zinc(II) complexes [Zn-2(ac)(3)(hmt)(2)(OH)]center dot H2O (1) and [{Zn-5(Obz)(8)(H2O)(2)(mu(3)-OH)(2)}(mu(2)-hmt) {Zn-2(Obz)(4)}center dot 6H(2)O](n) (2) have been synthesized using two different carboxylate salts (acetate (ac) for 1 and benzoate (Obz) for 2) and hexamethylenetetramine (hmt). Both the complexes have been structurally characterized by X-ray crystallography. Their identities have also been established by elemental analysis and IR spectral studies. Complex 1 is a dimer in which two zinc atoms contain equivalent four-coordinate tetrahedral environments. On the other hand, complex 2 is a 1D zig-zag coordination polymer containing alternative zinc pentamers and zinc dimers separated by bridging mu(2)-hmts. The cen-trosymmetric pentamer unit contains three independent zinc atoms, one being four-coordinate with a tetrahedral environment and other two being six-coordinate with octahedral geometries whereas the centrosymmetric dimer unit contains two five-coordinate Zn atoms with square pyramidal geometries. H-bonding interactions play a key role in stabilizing the observed structures. In complex 1, the water molecule is held within the dimer and in 2, a rare water hexamer is encapsulated in the supramolecular assembly by hydrogen bonds. The DFT calculations reveal that inter-and outer-cluster H-bond stabilization energies of water hexamer are -29.99 and -15.93 kcal/mol respectively. Lower stabilization energy from the ideal hexamer of chair conformer is attributed to the deformation of H-atoms as well as longer hydrogen bonded O center dot center dot center dot O distances. Additionally, the extra stability due to outer-cluster H-bonds is responsible for significant deformation from ideal chair conformer of hexamer cluster. (C) 2017 Elsevier B.V. All rights reserved.