Synthesis and first use of pyridine-2,6-diylbis(pyrazine-2-ylmethanone) in metal cluster chemistry: a {Mn(III)3Na2} complex with an ideal trigonal bipyramidal geometry.

The successful organic synthesis of a new dipyrazole/pyridine-dicarbonyl organic molecule, namely pyridine-2,6-diylbis(pyrazine-2-ylmethanone) [(pz)CO(py)CO(pz)], followed by its employment in Mn coordination chemistry has yielded the neutral cluster compound [Mn3Na2O(N3)3(L)3] (1), where L(2-) is the (pz)C(CH2COCH3)(O(-))(py)C(CH2COCH3)(O(-))(pz) dianion. The latter group was formed in situ, presumably by the nucleophilic attack of the carbanion (-)CH2COCH3 to the carbonyl carbon atoms of (pz)CO(py)CO(pz), in the presence of Mn(n+) ions under basic conditions and in solvent Me2CO. Complex 1 possesses an almost ideal trigonal bipyramidal topology, with the two Na(I) ions occupying the apical positions and the three Mn(III) ions residing in the equatorial trigonal plane. The bridging ligation about the metal ions is provided by a µ3-O(2-) ion and six µ-OR(-) groups from the L(2-) ligand, while peripheral ligation is completed by three terminal azido groups and the pyridine N and carbonyl O atoms of L(2-). Magnetic susceptibility studies revealed the presence of predominant antiferromagnetic exchange interactions between the paramagnetic Mn(III) centres; the use of an anisotropic, equilateral Mn(III)3 triangle model allowed us to fit the magnetic data and obtain the best-fit parameters: J = -10.8 cm(-1), D = -5.3 cm(-1), and g = 1.99. The combined results demonstrate the rich chemical reactivity of carbonyl groups and the ability of poly-ketone ligands to stabilize cluster compounds with unprecedented structural motifs and interesting architectures.

Supramolecular chains of high nuclearity {Mn(III)25} barrel-like single molecule magnets.

The first application of 1-methyl-1H-pyrrole-2-carbaldehyde oxime as a ligand for the coordination of paramagnetic transition metal ions has afforded a new {Mn(III)25} barrel-like cluster linked via Na(+) cations into a 1D polymeric topology that exhibits single-molecule magnetic behaviour.

2-Pyrrolyloximes in high-nuclearity transition-metal cluster chemistry: Fe10 and Fe12.

The employment of 2-pyrrolyloximes in high-nuclearity transition-metal cluster chemistry has provided access to unprecedented decanuclear and dodecanuclear Fe(III) cagelike clusters bearing the anion of pyrrole-2-carboxaldehyde oxime (praoH(2)), the simplest member of this new family of ligands; the identity of the products depends on the nature of the counteranion present in the starting materials.