The molecular structures of Au(2,2′-bpy)Cl 3·2.25H 2O and its 1-methyluracil adduct [Au(2,2′-bpy)( 1-MeU) 2] ClO 4·4H 2O

Abstract

The molecular structures and spectroscopic data (IR, 1H NMR) of two Au(III) complexes are reported, Au(2,2′-bpy)Cl 3·2.25H 2O ( 1) and [Au(2,2′-bpy)- (1-MeU) 2]ClO 4·4H 2O ( 2b) (1-MeU = 1-methyluracil anion, C 5H 5N 2O 2). 1 crystallizes in the space group C2/ c with a = 35.452(3), b = 7.701(1), c = 22.115(2) Å, β = 90.67(1)°, V = 6037.3 Å 3, Z = 16. 2b crystallizes in the space group P1 with a = 7.930(1), b = 12.606(1), c = 13.768(1) Å, α = 93.46(1)°, β = 102.62(1)°, γ = 96.74(1)°, V = 1328.5 Å 3, Z = 2. 1 is best described as consisting of dinuclear units, built up from two planar (2,2′-bpy)AuCl 2 entities that are connected via a long AuClAu bridge of 3.218(3) Å (AuCl, av.). The 2,2′-bpy rings are almost parallel and within the dinuclear unit c. 6.26 Å (av.) apart. 1 reacts with AgX and excess 1-MeU to give [Au(2,2′-bpy)(1-MeU) 2]X· nH 2O ( 2). In 2b (X = ClO 4 −, n = 4), the arrangement of the two 1-MeU ligands in the solid state is head-to tail, but 1H NMR suggests that in aqueous solution this rotamer coexists with the head-to-head species. Comparison of 2b with the corresponding Pt(II) and Pd(II) complexes reveals that, in its effect on the 1-MeU ring (internal ring angle at N3, IR spectrum, basicity of exocyclic oxygen, donor properties toward heterometals), the Au(III) electrophile behaves very much different and in this respect is close to the effect of a H +. Both in strongly acidic and strongly alkaline solution, 1-MeU is displaced from 2 to give [(2,2′-bpy)Au(1-MeU)(H 2O)] 2+ (5) and [(2,2′-bpy)Au(1-MeU)(OH)] + (5′), respectively.