Isolation of cationic digold-frame with free carboxylic acid pendants.

Use of different diphosphines enables the isolation and crystallographic characterization of gold pyridylcarboxylate complexes with different structural motifs. Dppm [bis(diphenylphosphino)methane] supports side-by-side-like complexes [Au(2)(dppm)(IsonicH)(2)](2+) (isonicH = 4-NC(5)H(4)CO(2)H) with aurophilic and pipi interactions of the pyridyl rings. Use of dppen [1,2-bis(diphenylphosphino)ethylene] removes the latter interaction but keeps the orthogonal closed-shell interaction of Au(I) in [Au(2)(dppen)(IsonicH)(2)](2+). The ligand dppe [1,2-bis(diphenylphosphino)ethane] helps to push the gold centers apart in [Au(2)(dppe)(isonicH)(2)](2+) and remove both interactions. These digold complexes are potential metalloligands that carry functional acids which can be conveniently activated by deprotonation.