Employment of methyl 2-pyridyl ketone oxime in 3d/4f-metal chemistry: dinuclear nickel(ii)/lanthanide(iii) species and complexes containing the metals in separate ions?

Dalton Transactions Pub Date: 2012-10-04 DOI: 10.1039/C2DT31928D

Abstract

The use of methyl 2-pyridyl ketone oxime (mpkoH) for the synthesis of NiII/LnIII (Ln = lanthanide) complexes, using “one-pot” reactions in the absence of an external base, is described. Depending on the reaction and crystallization conditions employed, two families of complexes have been obtained. The first family consists of true heterometallic species and involves complexes [NiLn(mpko)3(mpkoH)3](ClO4)2, where Ln = Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho and Er. The second family contains the pseudo heterometallic complexes [Ni(mpkoH)3]2[Ln(NO3)6](ClO4), where Ln = La, Ce, Pr, Nd and Sm. The crystal structures of [NiCe(mpko)3(mpkoH)3](ClO4)2 (1), [NiDy(mpko)3(mpkoH)3](ClO4)2 (8) and [Ni(mpkoH)3]2[La(NO3)6](ClO4) (11) have been determined by single-crystal, X-ray crystallography. Complexes 1·1.2MeOH·0.6H2O and 8·1.2MeOH·0.6H2O crystallise in the monoclinic space group P21/a and are isomorphous; there are two crystallographically independent cations in the unit cell, but their interatomic distances and angles differ little. The NiII and LnIII ions are bridged by three oximate groups belonging to the η1:η1:η1:μ mpko? ligands. The NiII centre is octahedrally coordinated by the six nitrogen atoms of the mpko? ligands in a facial arrangement. The LnIII centre is bound to an (Ooximate)3N6 set of donor atoms, the nitrogen atoms belonging to the three N,N′-bidentate chelating mpkoH ligands. The stereochemistry of the LnIII atoms has been evaluated by means of continuous shape measures (CShM). The two crystallographically independent CeIII atoms in 1 have tricapped trigonal prismatic and capped square antiprismatic coordination geometries, while the polyhedra of the DyIII atoms in 8 are both close to a tricapped trigonal prism. The octahedral NiII atoms in 11 are both facially bound to a N6 set of donor atoms from three N,N′-bidentate chelating mpkoH ligands, while the 12-coordinate LaIII centre in [La(NO3)6]3? is coordinated by six bidentate chelating nitrato groups. Variable-temperature, solid state dc magnetic susceptibility studies were carried out on complexes 2, 6, 7 and 8. The dc susceptibility data for 6 in the 2.0–300 K range have been fit to a model with one J value, revealing an antiferromagnetic NiII?GdIII exchange interaction [J = ?1.1 cm?1 based on H = ?J (?Ni·?Gd)]. Antiferromagnetic NiII?PrIII, NiII?TbIII and NiII?DyIII exchange interactions have also been suggested for 2, 7 and 8, respectively. The combined work demonstrates the usefulness of mpko? in the preparation of interesting NiII/LnIII compounds, without requiring the presence of external base and ancillary organic ligands.

Graphical abstract: Employment of methyl 2-pyridyl ketone oxime in 3d/4f-metal chemistry: dinuclear nickel(ii)/lanthanide(iii) species and complexes containing the metals in separate ions
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