The use of di-2-pyridyl ketone in manganese(II) benzoate chemistry: Two novel [formula omitted] linkage isomers containing the ketone form of the ligand and a neutral [formula omitted] cubane containing the ligand in its gem-diolate(-1) form

Abstract

The use of di-2-pyridyl ketone, (py) 2CO, in manganese(II) benzoate chemistry has yielded two Mn 3 II linkage isomers containing the ketone form of the ligand and a neutral Mn 4 II cubane cluster containing the gem-diolate(-1) form of the ligand. The 3:2 Mn(O 2CPh) 2 · 2H 2O/(py) 2CO reaction system in MeCN gives a mixture of the orange complex [Mn 3(O 2CPh) 6{(py) 2CO-κ 2 N, N′} 2] ( 1) and the yellow compound [Mn 3(O 2CPh) 6{(py) 2CO-κ 2 N, O} 2] · 2MeCN ( 2 · 2MeCN). The known compound [Mn 6O 2(O 2CPh) 10(MeCN) 4] ( 3) appears as a by-product when the initial reaction solution, that leads to 1 and 2 · 2MeCN, is allowed to slowly evaporate in the air. The trinuclear molecules adopt a linear structure in both complexes, with one monoatomically bridging η 1:η 1:μ 2 and two syn, syn-η 1:η 1:μ 2 carboxylate groups spanning each pair of Mn II ions. The terminal Mn II ions are each capped by one chelating- N, N′ (py) 2CO ligand in 1 and by one chelating- N, O (py) 2CO molecule in 2. The 1:1 reaction of Mn(O 2CPh) 2 · 2H 2O and (py) 2CO in CH 2Cl 2 results in the isolation of[Mn 4(O 2CPh) 4{(py) 2C(OH)O} 4] ( 4). The tetranuclear molecule has a cubane topology with the Mn II ions and the deprotonated oxygen atoms from the (py) 2C(OH)O − ligands occupying alternate vertices. The IR data are discussed in terms of the nature of the bonding. The magnetic properties of 4 in the 300–5 K range have been modeled with two J values and reveal weak intramolecular antiferromagnetic interactions. The low temperature X-band EPR spectra of 1, 2 and 4 are also discussed.