| Abstract: | The 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. |
