Comparative structural study of the complexation behaviour of silver(I), cadmium(II), mercury(II), and palladium(II) with a 17-membered N 3O 2-donor macrocycle

Abstract

A comparative investigation of the coordination behaviour of the 17-membered, N 3O 2-donor macrocycle, 1,12,15-triaza-3,4:9,10-dibenzo-5,8-dioxacycloheptadecane, L, with the soft metal ions Ag(I), Cd(II), Hg(II), and Pd(II) is reported. The X-ray structures of 12 complexes have been determined and a range of structural types, including both mononuclear and dinuclear species, shown to occur. In particular cases the effect of anion variation on the resulting structures has been investigated; L reacts with AgX (X = NO 3, ClO 4, PF 6, OTf and CN) to yield related 2:2 (metal:ligand) complexes of types [Ag 2 L 2(NO 3) 2] ( 1), [Ag 2 L 2](ClO 4) 2 · 2DMF ( 2), [Ag 2 L 2](PF 6) 2 · 2DMF ( 3), [Ag 2 L 2](OTf) 2 ( 4) and [Ag 2 L 2(μ-CN)][Ag(CN) 2] · H 2O ( 5). In all five complexes the ether oxygens of each ring are unbound. In 1–4 the macrocycles are present in sandwich-like arrangements that shield the dinuclear silver centres, with each silver bonded to two nitrogen donors from one L and one nitrogen from a second L. A Ag···Ag contact is present between each metal centre such that both centres can be described as showing distorted tetrahedral geometries. In the case of 5 a rare single μ 2- κC:κC symmetrically bridging two-electron-donating cyano bridge links silver ions [Ag···Ag distance, 2.7437(10) Å]; the macrocyclic ligands are orientated away from the dinuclear metal centres. In contrast to the behaviour of silver, reaction of cadmium(II) perchlorate with L resulted in a mononuclear sandwich-like complex of type [Cd L 2](ClO 4) 2 · CH 3CN ( 6). Again, the ether oxygens do not coordinate, with each L binding to the cadmium centre only via its three nitrogen donors in a facial arrangement such that a distorted octahedral coordination geometry is attained. Reaction of L with HgX 2 (X = ClO 4, SCN and I) yielded the monomeric species [Hg L(ClO 4) 2] ( 7), [Hg L(SCN) 2]·CH 3CN ( 8) and [Hg 2 L 2](HgI 4) 2 · 2 L ( 9), in which all five donors of L are bound to the respective mercury centres. However, reaction of L with Hg(NO 3) 2 in dichloromethane/methanol gave a mononuclear sandwich-like complex [Hg L 2 ](NO 3) 2 · 2CH 3OH ( 10) without anion coordination. Reaction of K 2PdCl 4 and Pd(NO 3) 2 with L yielded the 1:1 complexes [Pd LCl]Cl · H 2O ( 11) and [Pd L(NO 3)]NO 3 · CH 3OH ( 12), respectively, in which the metal is bound to three nitrogen donors from L along with the corresponding chloride or nitrate anion. Each palladium adopts a distorted square-planar coordination geometry; once again the ether oxygens are not coordinated.