ESI/MS of an acetonitrile solution containing a mixture of AgNO₃ :  bis(dicyclohexylphosphino)methane (dcpm, L) : NaO₂CH in a molar ratio of 2 : 1 : 1 gave an abundant peak due to [LAg₂(O₂CH)]⁺ and a minor peak assigned as [L₂Ag₄(O₂CH)₃]⁺. When this acetonitrile solution was frozen and layered with diethyl ether and left undisturbed for six days, crystalline material suitable for X-ray crystallography was identified and separated from amorphous solids. Single crystal X-ray diffraction revealed an unusual co-crystal consisting of two discrete tetranuclear silver clusters [(μ₂-dcpm)Ag₂(μ₂-O₂CH)(η²-NO₃)]₂·[(μ₂-dcpm)₂Ag₄(μ₂-NO₃)₄]. While all of the coordinated formates in [LAg₂(O₂CH)]⁺ and [L₂Ag₄(O₂CH)₃]⁺ can be decarboxylated in the gas-phase under conditions of collision induced dissociation, only the hydride [LAg₂(H)]⁺ thus formed reacts with formic acid via protonation and liberation of H₂ to regenerate to formate, thereby closing a catalytic cycle for the selective decomposition of formic acid.