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

Abstract

The use of di‐2‐pyridyl ketone oxime (Hpko)/X– “blends” (X– = PhCO2–, N3–, NCO–, acac–, NCS–) in zinc chemistry yields neutral tetranuclear and cationic pentanuclear clusters. Various synthetic procedures have led to the synthesis of compounds [Zn4(OH)2(O2CPh)2(pko)4]·3MeCN (1·3MeCN), [Zn4(OH)2(N3)2(pko)4]·4DMF (2·4DMF), [Zn4(OH)2(NCO)2(pko)4]·3DMF·H2O (3·3DMF·H2O), [Zn4(OH)2(acac)2(pko)4]·4CH2Cl2 (4·4CH2Cl2), [Zn5Cl2(pko)6][ZnCl(NCS)3]·2.5H2O·1.5MeOH (5·2.5H2O·1.5MeOH) and [Zn5(NCS)2(pko)6(MeOH)][Zn(NCS)4]·2.5H2O·MeOH (6·2.5H2O·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 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 Zn5 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)

Effect of Metal Dilution on the Thermal Spin Transition of [FexZn1–x(bapbpy)(NCS)2]

“…[21] The third Zn II center in the unit cell is coordinated by four thiocyanate ligands, thereby resulting in a distorted tetrahedral environment with N-Zn3-N angles that vary in the range 104.9-115.4°(see Tables 2 and 3), which is consistent with previously reported structure of this anion. [22][23][24] Furthermore, as depicted in Figure 8, there are three independent DMF solvent molecules in the asymmetric unit. One acts as a bifurcated hydrogen bond donor through O1, which is involved in two N-H···O hydrogenbonding interactions with the two N-H donor groups of the two crystallographically independent bapbpy ligands [N2B···O1 = 2.943(4) Å, N2A···O1 = 2.875(5) Å].…”

Investigation of the Zinc Chloride / Methyl(2-pyridyl)ketone Oxime Reaction System: A Mononuclear Complex and an Inverse 12-Metallacrown-4 Cluster

“…The metallacrown is characterized as inverse because the Zn atoms, rather than the oximato oxygen atoms, are oriented towards the center of the cavity. For 12-MC-4 complexes, two structural motifs have been reported: regular [6,23] and inverse [6,21,25,28,29,37], with most 12-MC-4 compounds belonging to the former type. In the regular motif, there is an -N-O-M-N-O-M-linkage, i. e., an -[M-N-O] n -repeat unit, with the oxygen atoms oriented towards the center of the cavity and capable of binding cations [6].…”

“…The cis arrangement of the oxime groups seems unfavourable, most probably due to the steric hindrance arising from the methyl group upon oxime coordination. The molecule has no imposed symmetry, although it approximates closely C 2 symmetry, with the C 2 axis bisecting the Cl(1)-Zn(1)-Cl (2) [39,40], pyridyl nitrogen [28, 39 -41] or oxime nitrogen atoms [28,41]. The distortion from perfect octahedral geometry is a consequence of the relatively small bite an- Compound 1 is the second structurally characterized zinc(II) complex of (py)C(Me)NOH, see Table 3.…”

“…Zinc(II) metallacrown complexes based on 2-pyridyloximate ligands have attracted some prior interest [21,25,28,37]; details will be given in "Results and Discussion". Seeking to extend the family of Zn(II) MCs incorporating new 2-pyridyloximate ligands and to examine the possibility of creating novel cluster topologies within this chemistry, we report here studies of the reactions of methyl 2-pyridyl ketone oxime [(py)C(Me)NOH, Fig.…”

“…We have been exploring the chemistry of MCs [28,29] and the coordination chemistry of 2-pyridyl oximes [(py)C(R)NOH, Fig. 1] [28 -34], the latter not necessarily in relation to the former.…”