One pot-synthesis of chiral Ni_6 clusters involving Ni _3 subunits: A combined structural, magnetic and DFT study

摘要

Ni_6 clusters of the general formula [{Ni_3L ~n(OAc)(OH)}_2(X)(OAc)(H_2O)_2] (n = 1, 2; X = Cl- or N_3-, (L~n)~(3-) = hexadentate tritopic ligands) can be isolated by spontaneous self-assembly, from mixtures of Ni(OAc)_2, H_3L~n, NMe _4OH·5H_2O and NaX in adequate molar ratios. Thus, four new hexanuclear complexes [{Ni_3L~1(OAc)(OH)} _2Cl(OAc)(H_2O)_2]·7.5H_2O (1·7.5H_2O), [{Ni_3L~2(OAc)(OH)} _2Cl(OAc)(H_2O)_2]·2H_2O· 7.5MeOH (2·2H_2O·7.5MeOH), [{Ni_3L ~1(OAc)(OH)}_2(N_3)(OAc)(H_2O) _2]·6H_2O (3·6H_2O) and [{Ni _3L~2(OAc)(OH)}_2(N_3)(OAc)(H _2O)_2]·4H_2O (4·4H_2O) were obtained and fully characterised. 1·7.5H_2O and 2·2H_2O·7.5MeOH were isolated in the form of single crystals, the latter losing solvate on drying, to yield 2·2H _2O. Recrystallisation of 3·6H_2O in MeCN/MeOH also generates single crystals of 3·H_2O·2MeOH·2MeCN. Their X-ray characterisation shows that these Ni_6 clusters can be considered to be built from two triangular trinuclear [Ni_3L ~n(OAc)(OH)]~+ subunits with different connectors. In addition, these studies demonstrate that the (L~n)~(3-) ligands behave as trinucleating, adopting such a conformation that induces chirality in the isolated compounds. In this way, 3·H _2O·2MeOH·2MeCN appears particularly interesting, since it emerges as homochiral after undergoing spontaneous resolution upon crystallisation. The magnetic characterisation of 1·7.5H_2O to 3·6H_2O 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.