A Systematic Exploration of Nickel–Pyrazolinato Chemistry with Alkali Metals: New Cages From Serendipitous Assembly

Abstract

AbstractThe preparation and properties of fourteen novel paramagnetic [NiIIx] aggregates bridged by pivalate, pyrazolinolate and in most cases hydroxide are reported. A rich structural diversity has been achieved by changing the nature of the alkali of the base used during the synthesis, leading to the nuclearities [NiII4NaI4] (2, 3, 4), [NiII5NaI4] (5, 6, 7), [NiII5LiI6] (8), [NiII8MI2] (M=K (9, 10), Rb (11, 12), Cs (13, 14) and [NiII8] (15). All compounds have been characterised by single‐crystal Xray diffraction; however, full crystallographic details are given only for the representative molecules [Ni4Na4(fpo)4(piv)8(Hpiv)8] (2), [Ni5Na4(OH)2(mpo)4(piv)8(Hpiv)2(MeCN)2] (5), [Ni5Li6(OH)2(fpo)2(piv)12(Hpiv)4] (8), [Ni8K2(OH)4(ppo)4(piv)10(Hppo)2(Hpiv)2(MeCN)2] (9), [Ni8Rb2(OH)4(ppo)4(piv)10(Hppo)2(Hpiv)2(MeCN)2] (11), [Ni8Cs2(OH)4(ppo)4(piv)10(Hppo)2(Hpiv)2(MeCN)2] (13) and [Ni8(OH)4(mpo)2(PhCH2CO2)10(Hmpo)8] (15). Variable‐temperature bulk magnetisation measurements have been performed for each type of complex. The [NiII4NaI4] clusters show intramolecular antiferromagnetic coupling and a spin ground state of S=0. Complexes of the type [NiII5NaI4] also display antiferromagnetic superexchange, leading to an S=1 spin ground state. The molecule with nuclearity [NiII5LiI6], in contrast, exhibits ferromagnetic interactions, resulting in the presence of low energy states with high multiplicity, and a spin ground state S>1. The [NiII8MI2] and [NiII8] clusters have the same topology of spin carriers, which display predominantly antiferromagnetic interactions to yield a diamagnetic ground state. The coupling within these octanuclear NiII clusters is rationalised in terms of the nature of the Ni‐O‐Ni angles within the core.