Linear [formula omitted] and cubane [formula omitted] carboxylate clusters derived from di-2-pyridyl ketone: Synthesis, characterization and magnetic properties

Abstract

The employment of di-2-pyridyl ketone, (py) 2CO, in manganese(II) benzoate chemistry is reported. The syntheses, crystal structures and spectroscopic (IR, EPR) characterization are described for [ Mn 3 II (O 2CPh) 6{(py) 2CO} 2] ( 1), [ Mn 3 II (O 2CPh) 6{(py) 2CO} 2] · 2MeCN ( 2 · 2MeCN) and [ Mn 4 II (O 2CPh) 4{(py) 2C(OH)O} 4] ( 3), where (py) 2C(OH)O − is the monoanion of the gem-diol form of (py) 2CO. Variable-temperature, magnetic susceptibility studies on 3 have also been performed. Complexes 1 and 2 · 2MeCN are linkage isomers. The trinuclear molecules of both complexes have a linear structure, with one η 1:η 2:μ 2 and two syn, syn- η 1:η 1:μ 2 PhCO 2 - groups spanning each pair of Mn II atoms. The terminal Mn II atoms are each capped by one κ 2 N,N′ (py) 2CO ligand in orange 1 and one κ 2 N,Ο (py) 2CO molecule in the yellow isomer 2 · 2MeCN. The molecule of 3 has a cubane topology with the Mn II centers and the deprotonated oxygen atoms from the η 1:η 3:η 1:μ 3 ligands occupying alternate vertices of the cube. A terminal monodentate PhCO 2 - group completes a distorted octahedral coordination at each Mn II atom. The IR data are discussed in terms of the coordination modes of the ligands that are present in the complexes. The X-band EPR spectra of powdered 1 and 2 at 4 K indicate that the populated spin states exhibit a zero-field splitting, while the spectrum of 3 at 18 K is consistent with the presence of magnetically interacting Mn II atoms in the solid state. The magnetic properties of 3 in the 300–5 K range have been modelled with two J values, which reveal weak antiferromagnetic interactions within the molecule. Some suggestions have been made concerning the great stability of complex 3.