Linear MnII 3 and cubane Mn II4 carboxylate clusters derived from di-2-pyridyl ketone: Synthesis, characterization and magnetic properties

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 [MnII3(O2CPh)6{(py)2CO}2] (1), [MnII3(O2CPh)6{(py)2CO}2]·2MeCN (2· 2MeCN) and [MnII4 (O2CPh)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 η1:η2:μ2 and two syn, syn- η1:η1:μ2 PhCO2- groups spanning each pair of MnII atoms. The terminal MnII atoms are each capped by one κ2 N,N' (py)2CO ligand in orange 1 and one κ2 N,O (py)2CO molecule in the yellow isomer 2·2MeCN. The molecule of 3 has a cubane topology with the MnII centers and the deprotonated oxygen atoms from the η1:η3:η1:μ3 ligands occupying alternate vertices of the cube. A terminal monodentate PhCO2- group completes a distorted octahedral coordination at each MnII atom. The IR data are discussed in terms of the coordination modes of the ligands that are present in the complexes. The Xband 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 MnII 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.