Wells-Dawson cages as molecular refrigerants

Five clusters with the general formula [Ni6Gd6(μ3-OH)2(μ2-OAc)2(O3PR)6(O2C(t)Bu)16], where R = methyl (1), phenyl (2), n-hexyl (3), benzyl (4), n-octyl (5), have been prepared. All of the clusters have a {Ni6Gd6P6} core that can be related to the Wells-Dawson ion. We have also prepared analogues where the gadolinium is replaced with diamagnetic yttrium: [Ni6Y6(μ3-OH)2(μ2-OAc)2(O3PR)6(O2C(t)Bu)16] (R = methyl (6), n-hexyl (7), benzyl (8), n-octyl (9)), allowing the magnetic exchange within the {Ni3} units to be analyzed by modeling as the sum of two noninteracting isosceles triangles. The variation in the magnetic entropy changes for magnetization (-ΔSM) among compounds 1-5 could be attributed not only to the molecular weight of the compounds but also to intramolecular magnetic interactions.