Di-2-pyridyl ketone oxime in zinc chemistry: Inverse 12-metallacrown-4 complexes and cationic pentanuclear clusters

The use of di-2-pyridyl ketone oxime (Hpko)/X-"blends" (X-PhCO2-, N-3(-), NCO-, acac(-), NCS-) in zinc chemistry yields neutral tetranuclear and cationic pentanuclear clusters. Various synthetic procedures have led to the synthesis of compounds [Zn-4(OH)(2)(O2CPh)(2)(pko)(4)]center dot 3MeCN (1 center dot-3MeCN), [Zn-4(OH)(2)(N-3)(2)(pko)(4)]center dot 4DMF (2.4DMF), [Zn-4(OH)(2)(NCO)(2)-(pko)(4)]center dot 3DMF center dot H2O center dot (3.3DMF center dot H2O), [Zn-4(OH)(2)(acac)(2)(pko)(4)]center dot 4CH(2)Cl(2) (4.4CH(2)Cl(2)), [Zn5Cl2(pko)(6)][ZnCl(NCS)(3)]center dot 2.5H(2)O center dot 1.5MeOH (5 center dot 2.5H(2)O center dot 1.5MeOH) and [Zn-5(NCS)(2)(pko)(6-)(MeOH)][Zn(NCS)(4)]center dot 2.5H(2)O center dot MeOH (6 center dot 2.5H(2)O-MeOH). The structures of the six complexes have been determined by single-crystal X-ray crystallography. The tetranuclear molecules of 1-4 lie on a crystallographic inversion centre and have an inverse 12-metallacrown-4 topology. Two triply bridging hydroxides are accommodated in the centre of the metallacrown ring. The pko(-) ligands form a propeller configuration that imposes absolute stereoisomerism with Delta and Delta chirality. Two metal ions are in distorted O2N4 octahedral environments, whereas the rest are in severely distorted tetrahedral or trigonal bipyramidal environments. The five Zn ions of the cations of 5 and 6 are held together by six pko(-) ligands which adopt three different coordination modes; the chloro (5) and isothiocyanato (6) ligands are terminal. The five Zn ions define two nearly equilateral triangles sharing a common apex, and the novel Zn-5 topology can be described as two "collapsed" 9-metallacrown-3 structures sharing a common Zn apex. Besides the pentanuclear cations, the structures of 5 and 6 contain slightly distorted tetrahedral [ZnCl(NCS)(3)](2-) and [Zn(NCS)(4)](2-) ions, respectively, with the isothiocyanato ligands binding the metal ion in a virtually linear fashion. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)