Density-functional theory and ab initio methods have been applied to characterize the structural features of Al-(SiO)(1,2) compounds. According with previous work [Schnockel , J. Chem. Phys. 112, 1444 (2000)], it has been shown that an Al atom spontaneously reacts with SiO forming a linear O-bonded molecule, AlOSi ((2)Pi). Three minima have been found in the potential-energy surface of Al-(SiO)(2): two local minima corresponding to cis-cis and to trans-trans forms with two equivalent SiO fragments arising from addition of a second SiO to AlOSi, and the third one corresponding to the global minimum with a chain structure. It has been shown that the chain structure could be obtained either spontaneously from the reaction between an aluminum atom and a cyclic (SiO)(2) dimer or from the isomerization reaction of the cis-cis Al-(SiO)(2) structure but requiring, in this case, an activation energy about 10 kcal/mol. Bonding characterization performed within topological frameworks reveals that the interaction in all the (SiO)(n) and Al-(SiO)(n) (n=1 and 2) compounds should be considered as a highly polar interaction. Structural comparisons have been made between Al-dicarbonyl and Al-disilonyl on the ground of the topological analysis. (C) 2003 American Institute of Physics.