A Silver(I)–Gold(II) Hexanuclear Guanidinate–Benzoate Cluster with Short Au–Au Bonds

Abstract

AbstractAttempts to remove the halide atoms from [Au 2 (hpp) 2 Cl 2 ], 1, Hhpp = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine, with Ag(I) benzoate lead to the formation of the Au(I)-Ag(I) product, [(PhCOO) 2 Au 4 (hpp) 4 Ag 2 (PhCOO) 4 ], 2. This material is stable to air and light at room temperature and shows a UV-vis spectrum in THF with absorbances at 575, 440, 345, and 273 nm. The mixed metal product crystallizes as green crystals in the monoclinic space group P2 1 /n. The Au-Au distances of 2.4473(19) A are the shortest gold-gold distances reported to date. The gold···silver distance is 3.344(3) A and the silver···silver distance is 2.771(6) A. This latter distance is short compared with the Ag···Ag distance of 2.902(3) A in the eight-membered silver benzoate dimer starting material. The Au(II) hpp and Ag(I) benzoate components are linked by carboxylate groups and two gold-silver interactions. This result stands in structural contrast to terminal carboxylate products observed with Au(II) ylides and amidinates wherein the carboxylate is not bridging to another metal atom.Index AbstractThree equivalents of silver benzoate react with [Au 2 (hpp) 2 Cl 2 ], 1, Hhpp = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine, to form the gold(II)-silver(I) product, 2, [(PhCOO) 2 Au 4 (hpp) 4 Ag 2 (PhCOO) 4 ]. The gold-gold distance of 2.4473(19) A is the shortest gold-gold distance reported to date. The gold-silver distance is 3.344(3) A and the silver-silver distance is 2.771(6) A.[IMAGE]