The hydrogen storage capacities of pi complex (Ti-eta(2)-(C2H2)) and the corresponding ethynyl metal hydrides (HC C-TiH) complex were tested using second order Moller Plesset method with 6-311++G(3df,3pd) basis sets. Both on Ti-eta(2)-(C2H2) and HC C-TiH, up to six hydrogen molecules can be absorbed with a binding energy of 0.20-0.42 eV/H-2, corresponding the maximal retrievable hydrogen storage density of 14.06 wt%. A comparative study of various density functional theory calculations showed that the averaged H-2 adsorption energy is not only considerably affected by the level of theory used but also dependent on the complex of the material dealing with. Dimerizations of the Ti acetylene complexes were also discussed. Copyright (c) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.