Synthesis, crystal structures and magnetic properties of trinuclear oxo-centered homo- and mixed-valence manganese pivalate complexes with imidazole (Im) and 1-methylimidazole (1-MeIm): [Mn₃^III0(0₂CCMe₃)₆ (Im)₃](Me₃CC0₂)•0.5Me₃CC0₂H and [Mn₂^IIIMn^II0(0₂CCMe₃)₆(1-MeIm)₃]

Two new μ₃-oxo-centered trinuclear manganese complexes, one of them a homo-valence [Mn₃^III0(0₂CCMe₃)₆ (Im)₃](Me₃CC0₂)•0.5Me₃CC0₂H (<b>1</b>) pivalate complex and the other a mixed-valence [Mn₂^IIIMn^II0(0₂CCMe₃)₆(1-MeIm)₃] (<b>2</b>) pivalate complex (where Im = imidazole, 1-MeIm = 1-methylimidazole), have been synthesized and characterized by IR spectroscopy, thermogravimetric analysis, X-ray crystallography and magnetochemistry. Complexes <b>1</b> and <b>2</b> are μ3-oxo-trinuclear compounds with the three manganese atoms bridged by six pivalate groups. At each axial position there is an Im (<b>1</b>) or 1-MeIm (<b>2</b>) molecule. In both compounds, the manganese coordination geometry is slightly distorted octahedral, consisting of the oxygen of the central triangle, four oxygen atoms from bridging pivalate ligands, and a terminal Im or 1-MeIm nitrogen atom. The crystal packing of <b>1</b> involves hydrogen bonding between complex cations [Mn₃O(Piv)₆(Im)₃]⁺ and outersphere pivalate ions, whereas in compound <b>2</b> interactions of the C–Hπ type, formed by both the aromatic and methyl C–H groups of 1-MeIm molecules, are present. Magnetic studies reveal that both compounds represent antiferromagnetically coupled, spin-frustrated triangular systems exhibiting weak to moderate exchange coupling constants.