The　pivotal　role　of　clusters　and　aromaticity　in　chemistry　is　undeniable,　but　there　remains　a　gap　in　systematically　understanding　the　aromaticity　of　metal-organic　clusters.　Herein,　this　article　presents　a　novel　metal-organic　π-cluster,　melding　both　metal-organic　chemistry　and　aromaticity,　to　guide　the　construction　of　structurally　stable　Os-organic　π-clusters.　An　in-depth　analysis　of　these　clusters　reveals　their　bonding　attributes,　π-electronic　composition,　and　origins　of　aromaticity,　thereby　confirming　their　unique　metal-organic　π-cluster　properties.　Furthermore,　the　Os5　cluster　exhibits　a　promising　third-order　nonlinear　optical　(NLO)　response,　attributable　to　its　narrow　band　gap　and　uniform　electron/hole　distribution,　suggesting　its　potential　as　an　optical　switching　material.　This　research　introduces　a　fresh　perspective　on　clusters,　centered　on　delocalization,　and　broadens　the　domain　of　aromaticity　studies.　It　also　presents　a　novel　method　for　designing　efficient　third-order　NLO　materials　through　consideration　of　the　structure-activity　relationship.　©　2024　The　Royal　Society　of　Chemistry.