The synthesis, properties, and the crystal and molecular structures of five-co-ordinate copper(I) and silver(I) complexes of a quinquedentate macrocyclic ligand having an ‘N3S2’ donor set

Abstract

The 17-membered macrocyclic ligand L¹ containing the ‘N₃S₂’ donor set has been synthesised [and isolated as the silver(I) complex] by the template action of silver(I) salts on the cyclic Schiff-base condensation of 2,6-diacetyl-pyridine with 1,10-diamine-4,7-dithiadecane. The copper(II) ion was ineffective as a template for the synthesis. However, copper(II) complexes of L¹ could be obtained from [AgL¹]⁺via metal exchange (transmetallation). Sodium tetraphenylborate is a reducing agent for [Cu^IIL¹]²⁺, affording [Cu^IL¹]+ in good yield. Possible mechanisms for the reducing action of [BPh₄]^– are discussed. Hydrogenation of [AgL¹]⁺ salts using Na[BH₄] give the free reduced macrocycle RL¹(i.e. L¹+ 4H) from which a new range of macrocyclic complexes may be obtained. Infrared and electronic spectra of the silver(I) and copper(I) complexes of L¹ are reported. The copper(I) complexes are unreactive to both O₂ and CO. Crystals of [CuL¹][ClO₄] are orthorhombic with a= 6.844(7), b= 12.361(11), c= 24.072(21)Å, Z= 4, and space group P2₁2₁2₁. Crystals of [AgL¹][BPh₄] are monoclinic with a= 13.132(11), b= 25.001(12), c= 12.479(12)Å, β=105.7(1)°, Z= 4, and space group P2₁/c. The two structures were solved by Patterson and Fourier methods from 927 and 2 621 reflections above background measured by diffractometer and refined by full-matrix least squares to R 0.077 and 0.071 respectively. While the co-ordination geometry of both complexes is a distorted trigonal bipyramid there are marked differences in the macrocycle conformations in the two cases and, for the copper(I) complex, in the metal–nitrogen bond lengths. These are discussed in relation to the sizes of the two metal ions and of the macrocycle hole size.