A Ni11 coordination cluster from the use of the di-2-pyridyl ketone/acetate ligand combination: synthetic, structural and magnetic studies

Abstract

The combined use of di-2-pyridyl ketone, (py)2CO, and acetates (MeCO2−) in nickel(II) chemistry in H2O-MeCN under basic conditions (Et3N) afforded the coordination cluster [Ni11(OH)6(O2CMe)12{(py)2C(OH)(O)}4(H2O)2] (1) in 80% yield, where (py)2C(OH)(O)− is the monoanion of the gem-diol form of (py)2CO. The complex contains a novel core topology. The core of 1 comprises a central non-linear {Ni3(μ2-OH)4}2+ subunit which is connected to two cubane {Ni4(OH)(μ3-OR)2(μ3-OR′)}4+ subunits [RO− = (py)2C(OH)(O)− and R′O− = MeCO2−] via the OH− groups of the former which become μ3. The linkage of the Ni3 subunit to each Ni4 subunit is completed by two η1:η1:μ2 and one η1:η3:μ4 MeCO2− groups. Peripheral ligation is provided by two terminal monodentate MeCO2− and two terminal aqua ligands. The (py)2C(OH)(O)− ligands adopt the η1:η1:η3:μ3 coordination mode. From the twelve MeCO2− ligands, two are η1, two η1:η3:μ4 and eight adopt the syn, syn η1:η1:μ2 coordination mode; four of the latter bridge NiII centers at opposite faces of the cubane subunits. Complex 1 is the largest nickel(II)/(py)2CO-based ligand coordination cluster discovered to date and has an extremely rare nuclearity (Ni11) in the cluster chemistry of nickel(II). Variable-temperature, solid state dc susceptibility, and variable-field magnetization studies at low temperatures were carried out on complex 1. The study of the data reveals an S = 3 ground state, which has been well rationalized in terms of known magnetostructural correlations and the structural features of 1. An attempt has also been made to interpret the magnetic properties of the undecanuclear cluster in a quantitative manner using four exchange interaction parameters and the obtained J values are discussed. The role of H2O in the solvent medium that led to 1, and the high nickel(II) and acetate to di-2-pyridyl ketone reaction ratio employed for its preparation, on the nuclearity and identity of the cluster are critically analyzed.