Syntheses and structures of a family of heterometallic pentanuclear [MnIII3LnNa] (Ln = Dy, Tb, Gd and Nd) complexes: H-bonding reduces the nuclearity from nine to five

Abstract

The reaction of a multisite coordination ligand (LH₃) with LnCl₃·6H₂O, followed by the addition of Mn(OAc)₂·4H₂O, sodium azide and pivalic acid in the presence of triethylamine in a 2 : 1 : 1 : 4 : 4 : 6 (LH₃ : LnCl₃ : Mn(OAc)₂ : NaN₃ : pivalic acid : Et₃N) stoichiometric ratio afforded a series of heterometallic pentanuclear neutral complexes containing a [Mn^III₃LnNa] core {Ln = Dy (1), Tb (2), Gd (3) and Nd (4)}. The oxidation states of the Mn^III ions were confirmed by BVS calculation. All the complexes were characterized by X-ray crystallography. The pentametallic aggregates form a trigonal-bipyramidal geometry in which the three Mn^III ions are in the equatorial plane whereas the sodium and lanthanide ions are in the apical positions. Three different types of Mn^III ions are present in the complexes and all are in a distorted octahedral geometry. An all-oxygen environment is found to be present around the lanthanides as well as the sodium ions. The lanthanide ion is eight-coordinated and in distorted dodecahedral geometry, while the sodium ion is six-coordinate in a distorted trigonal prismatic geometry in 1–4. The pentanuclear core [Mn^III₃LnNa] is a subset of one-half of the nonanuclear ensemble, [Mn^III₆LnNa₂]⁺, reported in literature. We propose that the reduction in the nuclearity of the heterometallic metal ensemble occurs as a result of the influence of hydrogen bonding interactions present in the system.