Density　functional　theory　and　coupled　cluster　theory　calculations　are　carried　out　to　investigate　the　electronic　and　structural　properties　of　a　series　of　mononiobium　sulfide　clusters,　NbSn2-/-/0　(n　=　3-5).　Generalized　Koopmans＇　Theorem　is　applied　to　predict　the　vertical　detachment　energies　and　simulate　the　corresponding　photoelectron　spectra.　The　evolutions　of　geometric　and　electronic　structures　of　NbSn2-/-/0　(n　=　3-5)　clusters　with　changes　in　sulfur　content　and　charge　states　are　illustrated.　Intriguingly,　diverse　polysulfide　ligands　emerge　in　the　corresponding　sulfur-rich　clusters,　and　distinct　differences　in　the　geometric　and　electronic　structures　influenced　by　charge　states　are　exhibited,　especially　for　the　NbS52-/-/0　clusters.　In　addition,　the　NbSn2-/-　are　compared　with　the　corresponding　MoSn-/0　clusters.　Similar　structural　evolution　and　behavior　of　sequential　sulfidation　as　a　function　of　S　content　are　indicated　for　these　two　valence-isoelectronic　systems.　Molecular　orbital　analyses　are　performed　to　analyze　the　chemical　bonding　in　these　niobium　sulfide　clusters　and　to　elucidate　their　electronic　and　structural　evolutions.