Chemical and biological studies of gold(III) complexes with uninegative bidentate N–N ligands

Three new gold(III) complexes with uninegative bidentate N–N ligands ([Au(pla)Cl2](1), Hpla = picolinamide; [{Au(pz)Cl2}2](2), Hpz = pyrazole; [{Au(mpz)Cl2}2](3), Hmpz = 3-methylpyrazole) have been synthesized and characterized spectroscopically. The crystal structure of 1 contains one five-membered chelated ring and two cis-oriented chloride anions. It is the closest Au(III) analogue to cisplatin with an N–H group in the molecule and it forms a hydrogen bond with the carbonyl from adjacent molecule. The crystal structure of 2 shows a symmetrical six-membered Au(N–N)2Au ring. The two N–N bridging bonds and two gold atoms adopt a boat conformation, a configuration which thermodynamically stabilizes the complex. The two gold centres are square planar, each coordinated by two cis-oriented chlorides and nitrogens, respectively. These three new complexes have been tested for cytotoxic properties in vitro against MOLT-4 (human leukemia) and C2C12 (mouse tumour) cell lines. The results show that these complexes are slightly more cytotoxic than the clinically used cisplatin.