Alkali-Metal-Templated Assembly of Two High-Nuclearity Cobalt Clusters Based on Thiacalix[4]arene

Two
novel thiacalix[4]­arene-based high-nuclearity cobalt clusters,
[Na2Co24(BTC4A)6(PO4)6(HCOO)6(DMC)2(DMF)2(dma)4]·5DMF·9CH3OH (denoted as Na2@Co24, 1) and [KCo24(BTC4A)6(PO4)6(Cl)2(HCOO)4(DMF)8]­[KCo24(BTC4A)6(PO4)6(Cl)2(HCOO)6(DMF)4(CH3OH)2]·8DMF·23CH3OH (denoted
as K@Co24, 2) (H4BTC4A = p-tert-butylthiacalix­[4]­arene, DMC = N,N′-dimethylcarbamic acid anion, dma = dimethylamine),
have been solvothermally prepared and structurally characterized.
Compounds 1 and 2 are each capped by six
Co4-BTC4A molecular building blocks (MBBs) and six phosphate
linkers and other different auxiliary anions, possessing an eicositetranuclear
Co24 core templated by alkali-metal cations. In essence,
compound 1 is templated by two Na+ cations
with an attractive interaction in the center of the core, while 2 is templated by one K+ with a larger radius.
Such differences “convert” an oval-shaped Co24 disklike core in 1 to a circular core in 2. Interestingly, 2 contains both anionic and cationic
KCo24 cores, representing the largest cobalt aggregate
salt reported, to the best of our knowledge. In addition, magnetic
measurements of 1 and 2 were investigated,
revealing the existence of antiferromagnetic interactions between
the magnetic CoII centers.