Five clusters with the general formula [Ni6Gd6(mu(3)-OH)(2)(mu(2)-OAc)(2)(O3PR)(6)((O2CBu)-Bu-t)(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(mu(3)-OH)(2)(mu(2)-OAc)(2)(O3PR)(6)((O2CBu)-Bu-t)(16)] (R = methyl (6), n-hexyl (7), benzyl (8), n-octyl (9)), allowing the magnetic exchange within the {Ni-3} units to be analyzed by modeling as the sum of two noninteracting isosceles triangles. The variation in the magnetic entropy changes for magnetization (-Delta S-M) among compounds 1-5 could be attributed not only to the molecular weight of the compounds but also to intramolecular magnetic interactions.