One pot-synthesis of chiral Ni6clusters involving Ni3 subunits: a combined structural, magnetic and DFT study

Abstract

Ni₆ clusters of the general formula [{Ni₃Lⁿ(OAc)(OH)}₂(X)(OAc)(H₂O)₂] (n = 1, 2; X = Cl⁻ or N₃⁻, (Lⁿ)³⁻ = hexadentate tritopic ligands) can be isolated by spontaneous self-assembly, from mixtures of Ni(OAc)₂, H₃Lⁿ, NMe₄OH·5H₂O and NaX in adequate molar ratios. Thus, four new hexanuclear complexes [{Ni₃L¹(OAc)(OH)}₂Cl(OAc)(H₂O)₂]·7.5H₂O (1·7.5H₂O), [{Ni₃L²(OAc)(OH)}₂Cl(OAc)(H₂O)₂]·2H₂O·7.5MeOH (2·2H₂O·7.5MeOH), [{Ni₃L¹(OAc)(OH)}₂(N₃)(OAc)(H₂O)₂]·6H₂O (3·6H₂O) and [{Ni₃L²(OAc)(OH)}₂(N₃)(OAc)(H₂O)₂]·4H₂O (4·4H₂O) were obtained and fully characterised. 1·7.5H₂O and 2·2H₂O·7.5MeOH were isolated in the form of single crystals, the latter losing solvate on drying, to yield 2·2H₂O. Recrystallisation of 3·6H₂O in MeCN/MeOH also generates single crystals of 3·H₂O·2MeOH·2MeCN. Their X-ray characterisation shows that these Ni₆ clusters can be considered to be built from two triangular trinuclear [Ni₃Lⁿ(OAc)(OH)]⁺ subunits with different connectors. In addition, these studies demonstrate that the (Lⁿ)³⁻ ligands behave as trinucleating, adopting such a conformation that induces chirality in the isolated compounds. In this way, 3·H₂O·2MeOH·2MeCN appears particularly interesting, since it emerges as homochiral after undergoing spontaneous resolution upon crystallisation. The magnetic characterisation of 1·7.5H₂O to 3·6H₂O reveals that the three compounds present an overall antiferromagnetic coupling. The intricate magnetic behaviour of these clusters, mediated by a total of 14 bridges of different kinds, was analysed and satisfactorily interpreted in light of DFT calculations.