Theoretical calculations at MP2/6-311++G(d, p), MP2/6-311++G(2d, 2p), MP2/aug-cc-pVDZ and SCS-MP2/6-311++G(d, p) levels have been used to prove the existence of p-systems as sodium bond donors in pi center dot center dot center dot Na-Y(pi-systems: acetylene, ethylene, and benzene; Y = H, OH, and F) complexes. By comparison with some related systems, it can be concluded that the strength of the pi center dot center dot center dot X-Y (X = H, Li, and Na) bonds increased in the order hydrogen < sodium < lithium. The results of natural energy decomposition analysis (NEDA) show that the C2H2, C2H4 and C6H6 systems are mainly formed by electrostatic interaction, except for Complex-III1, which is dominated by the CT energy component. Furthermore, NBO analyse are applied to investigate the nature of the interaction. (C) 2011 Elsevier B. V. All rights reserved.