A MnII4cubane and a novel MnII10MnIII4cluster from the use of di-2-pyridyl ketone in manganese acetate chemistry

Abstract

The employment of di-2-pyridyl ketone, (py)₂CO, in manganese(II) acetate chemistry is reported. The syntheses, crystal structures and magnetochemical characterisation are described for [Mn^II₄(O₂CMe)₄{(py)₂C(OH)O}₄] (1) and [Mn^II₁₀Mn^III₄O₄(O₂CMe)₂₀{(py)₂C(OH)O}₄] (2), where (py)₂C(OH)O⁻ is the monoanion of the gem-diol form of the ligand. The reaction of Mn(O₂CMe)₂·4H₂O with one equivalent of (py)₂CO in Me₂CO gives 1. Complex 2 was obtained from the 1 : 1 reaction, in EtOH, between Mn(O₂CMe)₂·4H₂O and (py)₂CO in the presence of NEt₃. The tetranuclear molecule 1 has a cubane topology with the Mn^II and the deprotonated oxygen atoms from the η¹:η³:η¹:μ₃ ligands occupying alternate vertices of the cube. The core of 2 consists of two mixed valence cubane {Mn^II₂Mn^III₂(μ₃-O)₂(μ₃-OR″)₂}⁴⁺ subunits that are linked through an unusual {Mn^II₆(η¹:η²:μ-O₂CMe)₆(η²:η²:μ₃-O₂CMe)₂}⁴⁺ moiety via twelve η¹:η¹:μ MeCO₂⁻groups. Some suggestions have been made concerning the possible assembly of 2 from 1. The magnetic properties of 1 in the 300–5 K range have been modelled with two J values, which reveal weak antiferromagnetic interactions within the molecule. Complex 2 has a low spin ground state. This work demonstrates the flexibility, versatility and synthetic potential of combining (py)₂CO with carboxylate ligands.