Chemical　etching　of　nano-sized　metal　clusters　at　the　atomic　level　has　a　high　potential　for　creating　metal　number-specific　structures　and　functions　that　are　difficult　to　achieve　with　bottom-up　synthesis　methods.　In　particular,　precisely　etching　metal　atoms　one　by　one　from　nonmetallic　element-centred　metal　clusters　and　elucidating　the　relationship　between　their　well-defined　structures,　and　chemical　and　physical　properties　will　facilitate　future　materials　design　for　metal　clusters.　Here　we　report　the　single-gold　etching　at　a　hypercarbon　centre　in　gold(I)　clusters.　Specifically,　C-centred　hexagold(I)　clusters　protected　by　chiral　N-heterocyclic　carbenes　are　etched　with　bisphosphine　to　yield　C-centred　pentagold(I)　(CAu5I)　clusters.　The　CAu5I　clusters　exhibit　an　unusually　large　bathochromic　shift　in　luminescence,　which　is　reproduced　theoretically.　The　etching　mechanism　is　experimentally　and　theoretically　suggested　to　be　a　tandem　dissociation-association-elimination　pathway.　Furthermore,　the　vacant　site　of　the　central　carbon　of　the　CAu5I　cluster　can　accommodate　AuCl,　allowing　for　post-functionalisation　of　the　C-centred　gold(I)　clusters.