The structure, cohesive energy and electronic properties of MSin clusters were studied by first-principles calculations as a function of size (n) and species (M). We investigated 168 different clusters, containing from I to 14 Si atoms together with one transition metal atom among 12 different elements: Ti, Zr, Hf, V, Nb, Ta, Ni, Pd, Pt, Cu, Ag, An. Clusters with n-7, 10, 12 appear as local maxima in cohesive energy, independently of the metal involved. This, together with our previous findings for MSin (containing 12 other transition metal elements), establishes a systematic behavior. For most metals, MSi12 and MSi10 (the smallest endohedral species) are highly symmetric and exhibit local (with respect to their neighbors in size) stability. Thus, besides practically all MSi12 clusters (exceptions being HfSi12, ZrSi12), also some MSi10 such as VSi10, NiSi10, PdSi10, NbSi10 and AgSi10, are promising candidates as building blocks for cluster assembled materials. Electronic properties of structurally equivalent clusters depend markedly on the transition metal involved, providing the means to tailor pre-defined properties when designing extended phases. (c) 2006 Elsevier B.V. All rights reserved.