Preparation and characterisation of divalent hard and soft metal (M = Ca, Co, Cu, Zn, Cd, Hg and Pb) complexes of 1,10-dithia-18-crown-6: structural versatility

A range of divalent metal complexes (1-10) of 1,10-dithia-18-crown-6 (L) were synthesised in benzonitrile and structurally characterised. In particular cases (Cd, Hg and Pb), the anion effect on the resulting structures was investigated. The calcium(II) complex [Ca(L)(ClO4)(2)] (1) for L, adopting an 'egg-in-nest' conformation was isolated. The calcium centre is six-coordinate with a distorted trigonal prismatic geometry, being bound to four oxygens of L and two perchlorato ligands. When Co(ClO4)(2)center dot 6H(2)O was employed, the purple complex [Co(L)(H2O)(3)](2)(ClO4)(4) (2a) with a distorted octahedral geometry was obtained as a kinetic product, which then transformed to the solvato-complex [Co(C6H5CN)(4)(H2O)(2)](ClO4)(2) (2b, yellow) as a thermodynamic product. In contrast to 2a, the reaction with Cu(ClO4)(2)center dot 6H(2)O afforded an anion-coordinated complex [Cu(L)(ClO4)(2)]center dot 2C(6)H(5)CN (3). In 3, the copper centre is also six-coordinate, being bound to two oxygens and two sulfurs from L, in which the distorted octahedral geometry is completed by two perchlorato ligands. Reaction of L with Zn(ClO4)(2)center dot 6H(2)O yielded the mononuclear species [Zn(L)(H2O)(3)](2)(ClO4)(4) (4), in which the octahedral geometry of the zinc(II) is almost same as that of 2a. L reacts with CdX2 (X = ClO4 and NO3) to yield [Cd(L)(ClO4)(2)] (5) and [Cd(L)(NO3)] 2[Cd(NO3)(4)] (6), respectively. In perchlorato-complex 5, all six donors in L participate in the coordination sphere, in which the eight-coordinated 'tight and bent' conformation is completed by two perchlorate ions, adopting a dicapped trigonal prismatic geometry. Interestingly, the nitrato-complex 6 features three separated units of formula [Cd(L)(NO3)](2)[Cd(NO3) 4]: two macrocyclic complex cation units and one cadmium quadru-nitrato complex anion unit. In the reaction with HgX2 (X = ClO4 and NO3), L afforded an unusual triple-decker type dinuclear complex [Hg-2(L)(3)](ClO4)(4) (7) with 3 : 2 (L: M) stoichiometry and a 1 : 1 complex [Hg(L)(NO3)(2)]center dot 2H(2)O (8) with an eight-coordinate mercury centre, adopting a distorted hexagonal bipyramidal geometry. L reacts with PbX2 (X = ClO4 and NO3) to yield [Pb(L)(ClO4)(2)] (9) and [Pb(L)(NO3)(2)] (10). In 9, the lead(II) is six-coordinate, being bound to four oxygens, in which the distorted octahedral geometry is completed by two perchlorato ligands. In 10, the lead(II) coordinates to four oxygens together with two bidentate nitrato-ligands to yield an overall metal coordination geometry of eight, adopting the 'egg-in-nest' conformation again.