Linear Mn3II and cubane Mn4II 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 [Mn3II (O2CPh)6{(py)2CO}2] (1), [Mn3II (O2CPh)6{(py)2CO}2] · 2MeCN (2 · 2MeCN) and [Mn4II (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:μ2PhCO2- groups spanning each pair of MnII atoms. The terminal MnII atoms are each capped by one κ2N,N′ (py)2CO ligand in orange 1 and one κ2N,Ο (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 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 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.

Graphical abstractThe full synthetic investigation of the Mn(O2CPh)2·2H2O/di-2-pyridyl ketone reaction system has led to two interesting Mn3II linkage isomers containing the ketone form of the ligand and to one Mn4II cubane containing the singly deprotonated gem-diol form of the ligand; the complexes have interesting properties.Figure optionsDownload full-size imageDownload as PowerPoint slide