Au 2(μ-G)(μ-dmpe)] · (KBr) 0.75 · 2H 2O, a cyclic dinuclear gold(I) complex with an N3,N9-bridging coordination mode of guanine and aurophilic interactions: synthesis, X-ray crystal structure and luminescence properties (dmpe=1,2-bis(dimethylphosphino)ethane and G=guaninato dianion)

Abstract

The digold complex [Au 2(μ-G)(μ-dmpe)](KBr) 0.75 · 2H 2O (dmpe=1,2-bis(dimethylphosphino)ethane ( 1)) has been prepared by nucleophilic attack of the guaninate dianion on the gold(I) atoms of [(AuBr) 2(μ-dmpe)] and has been characterised by X-ray crystallography and spectroscopic studies. The structure of 1 consists of dinuclear nine-membered ring molecules, K + cations, Br − anions and water molecules, all of them involved in either weak K⋯O or hydrogen bonding interactions. Within the cyclic dinuclear molecules, gold(I) atoms are bridged on one side by the diphosphine ligand and on the other side by a doubly deprotonated guaninate anion coordinated through neighbouring N3 and N9 nitrogen atoms, with gold(I)⋯gold(I) interactions of 3.030(2) Å. This is the first X-ray example showing an N3,N9-bridging mode for guanine. There are two types of K + cations in the structure, K1 and K2. The former interacts with water molecules to form a unique [K(H 2O) 3(μ-H 2O) 2K(H 2O) 3] 2+ dipotassium unit whereas K2 interact with the O6 atom of the guaninate ligands and oxygen atoms of the dipotassium unit leading to a chain running along the c-axis. Each chain is interdigitated with four neighbouring ones to give rise to an intricate network in which Br1, Br2 and [K(H 2O) 3(μ-H 2O) 2K(H 2O) 3] 2+ fit snugly into cavities defined by digold molecules. Complex 1 luminescence at room temperature and 77 K in the solid state with excitation maxima at 385 nm and emission maxima at 451.8 and 448.7 nm, respectively. The emission spectrum of a saturated solution of 1 in DMSO (dimethyl sulfoxide) shows the maximum at about 440 nm.