Di‐2‐pyridyl Ketone Oxime in Zinc Chemistry: Inverse 12‐Metallacrown‐4 Complexes and Cationic Pentanuclear Clusters

Abstract

Abstract The use of di‐2‐pyridyl ketone oxime (Hpko)/X – “blends” (X – = PhCO 2 – , 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 (O 2 CPh) 2 (pko) 4 ] · 3MeCN ( 1· 3MeCN), [Zn 4 (OH) 2 (N 3 ) 2 (pko) 4 ] · 4DMF ( 2· 4DMF), [Zn 4 (OH) 2 (NCO) 2 (pko) 4 ] · 3DMF · H 2 O ( 3· 3DMF · H 2 O), [Zn 4 (OH) 2 (acac) 2 (pko) 4 ] · 4CH 2 Cl 2 ( 4· 4CH 2 Cl 2 ), [Zn 5 Cl 2 (pko) 6 ][ZnCl(NCS) 3 ] · 2.5H 2 O · 1.5MeOH ( 5· 2.5H 2 O · 1.5MeOH) and [Zn 5 (NCS) 2 (pko) 6 (MeOH)][Zn(NCS) 4 ] · 2.5H 2 O · MeOH ( 6· 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 Λ and Δ chirality. Two metal ions are in distorted O 2 N 4 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. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)