[Au(2)(micro-G)(micro-dmpe)].(KBr)(0.75) 2H(2)O, 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).

The digold complex [Au(2)(micro-G)(micro-dmpe)](KBr)(0.75) x 2H(2)O (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)(micro-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) A. 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(2)O)(3)(micro-H(2)O)(2)K(H(2)O)(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(2)O)(3)(micro-H(2)O)(2)K(H(2)O)(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.