An unusual co-crystal [(μ-dcpm)Ag(μ-OCH)(η-NO)]·[(μ-dcpm)Ag(μ-NO)] and its connection to the selective decarboxylation of formic acid in the gas phase.

ESI/MS of an acetonitrile solution containing a mixture of AgNO :  bis(dicyclohexylphosphino)methane (dcpm, L) : NaOCH in a molar ratio of 2 : 1 : 1 gave an abundant peak due to [LAg(OCH)] and a minor peak assigned as [LAg(OCH)]. 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 [(μ-dcpm)Ag(μ-OCH)(η-NO)]·[(μ-dcpm)Ag(μ-NO)]. While all of the coordinated formates in [LAg(OCH)] and [LAg(OCH)] can be decarboxylated in the gas-phase under conditions of collision induced dissociation, only the hydride [LAg(H)] thus formed reacts with formic acid via protonation and liberation of H to regenerate to formate, thereby closing a catalytic cycle for the selective decomposition of formic acid.