The hydrogen storage capacities of synthesized Scandium-Acetylene systems (Sc-eta(2) -(C2H2) and HC C-ScH) are tested by using density functional theory (DFT) and the coupled-cluster theory (CCSD (T)) with 6-311++G (3df, 3pd) basis sets. Both the energy profile and natural bond orbital analysis predict that Sc-eta(2)-C2H2 and HC C-ScH complexes are promising hydrogen storage materials. The Sc-eta(2)-(C2H2) and HC C-ScH complexes can trap up to six hydrogen molecules, reaching gravimetric uptake capacities as high as 14.56 wt%. Thermo-chemistry calculations indicate two H-2 in Sc-eta(2)-C2H2(H-2)(6) and four H-2 in HC C-ScH(H-2)(6) can be readily adsorbed at 77 K and desorbed at 298.15 K under atmospheric pressure, corresponding to the maximal reversible hydrogen storage abilities of 5.37 and 10.20 wt%, respectively. The further comparison between HC C -ScH(H-2) and HC C-ScH- (2H) reveals that the charged state of Sc atom has a great influence on the hydrogen adsorption state and adsorption energy. Moreover, dimers may form in case of scandium-acetylene systems. The most stable (C2H2Sc)(2) can adsorb ten H-2 molecules, reaching the hydrogen storage capacity of 12.43 wt%. Thermo-chemistry calculations indicate the maximal reversible hydrogen storage capacities of Sc(C2H2)(2) and (C2H2Sc)(2) are 7.67 and 7.85 wt%, respectively. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.