The geometric feature and chemical bonding of isoelectronic systems Si(8)N(6)Mq (M = V, Cr, Mn and q = -1, 0, 1, respectively) are investigated by means of density-functional-theory calculations. The encapsulated form is found for all ground-state structures, where the metal atom locates at the central site of the hollow Si8N6 cage. The Si8N6 cage is established by adding two Si atoms to a distorted Si6N6 prism, which is a combination of Si4N2 and Si2N4 strings. Chemical bonding of Si(8)N(6)Mq systems is explored by using the electron localization indicator and theory of atom in molecule, revealing the vital role of metal center in stabilizing the clusters. (C) 2017 Elsevier B. V. All rights reserved.