On the Hydrogen Oxalate Binding Motifs onto Dinuclear Cu and Ag Metal Phosphine Complexes

We report the binding geometries of the isomers that are formed when the hydrogen oxalate ((CO2)2H=HOx) anion attaches to dinuclear coinage metal phosphine complexes of the form [M1M2dcpm2(HOx)]+ with M=Cu, Ag and dcpm=bis(dicyclohexylphosphino)methane, abbreviated [MM]+. These structures are established by comparison of isomer‐selective experimental vibrational band patterns displayed by the cryogenically cooled and N2‐tagged cations with DFT calculations of the predicted spectra for various local minima. Two isomeric classes are identified that feature either attachment of the carboxylate oxygen atoms to the two metal centers (end‐on docking) or attachment of oxygen atoms on different carbon atoms asymmetrically to the metal ions (side‐on docking). Within each class, there are additional isomeric variations according to the orientation of the OH group. This behavior indicates that HOx undergoes strong and directional coordination to [CuCu]+ but adopts a more flexible coordination to [AgAg]+. Infrared spectra of the bare ions, fragmentation thresholds and ion mobility measurements are reported to explore the behaviors of the complexes at ambient temperature. To characterize the binding motifs of hydrogen oxalate (HOx) onto copper (Cu) and silver (Ag) phosphine complexes, we have invastigated [M1M2dcpm2(HOx)]+ (M=Cu, Ag; dcpm=bis(dicyclohexylphosphino)methane; abbreviated [CuCu]+ and [AgAg]+) in isolation. The 40 K N2 tagged IR‐PD spectra gives evidence for two isomers of [CuCu]+ and three isomers of [AgAg]+, supported by DFT calculations. Two color IR‐IR hole burning experiments indicate some minor amount of isomeric interconversions in [AgAg]+, whereas [CuCu]+ reveals a stiffer HOx coordination.