The use of di-2-pyridyl ketone in manganese(II) benzoate chemistry: Two novel Mn_3~(II) linkage isomers containing the ketone form of the ligand and a neutral Mn_4~(II) cubane containing the ligand in its gem-diolate(-1) form

摘要

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(O2CPh)2 · 2H2O/(py)2CO reaction system in MeCN gives a mixture of the orange complex [Mn3(O2CPh)6{(py)2CO-κ~2N,N'}2] (1) and the yellow compound [Mn3(O2CPh)6{(py)2CO-κ~2N,O}2] · 2MeCN (2 · 2MeCN). The known compound [Mn6O2(O2CPh)_(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:μ2 and two syn,syn-η~1:η~1:μ2 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(O2CPh)2 · 2H2O and (py)2CO in CH2Cl2 results in the isolation of [Mn4(O2CPh)4{(py)2C(OH)O}4] (4). The tetranuclear molecule has a cubane topology with the Mn~(II) ions and the depro-tonated 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.