Four heterometallic, enneanuclear Mn
8Ce clusters [Mn
8CeO
8(O
2CMe)
12(H
2O)
4] (
4), [Mn
8CeO
8(O
2CMe)
12(py)
4] (
5), [Mn
8CeO
8(O
2CPh)
12(MeCN)
4] [Mn
8CeO
8(O
2CPh)
12(dioxane)
4] (
6), and [Mn
8CeO
8(O
2CCHPh
2)
12(H
2O)
4] (
7) have been prepared by various methods. Their cores are essentially isostructural and comprise a nonplanar, saddlelike [Mn
III8O
8]
8+ loop containing a central Ce
IV ion attached to the eight μ
3-O
2− ions. Peripheral ligation around the [Mn
8CeO
8]
12+ core is provided by eight μ- and four μ
3-O
2CR
− groups. Terminal ligation on four Mn
III atoms is provided by H
2O in
4 and
7, pyridine in
5, and MeCN/dioxane in
6. Solid-state magnetic susceptibility studies, fits of dc magnetization vs field and temperature data, and in-phase ac susceptibility studies in a zero dc field have established that complexes
4,
5, and
7 possess
S = 16,
S = 4 or 5, and
S = 6
![](http://pubs.acs.org/images/entities/plusmn.gif)
1 spin ground states, respectively, but in all cases there are very low-lying excited states. The large variation in the ground-state spins for this isostructural family is rationalized as due to a combination of weak exchange interactions between the constituent Mn
III atoms, and the presence of both nearest-neighbor and next-nearest-interactions of comparable magnitudes. Magnetization vs applied dc field sweeps on single crystals of
4·4H
2O and
7·4H
2O·3MeCN·2CH
2Cl
2 down to 0.04 K have established that these two complexes are new single-molecule magnets (SMMs). The former also shows an exchange-bias, a perturbation of its single-molecule properties from very weak intermolecular interactions mediated by hydrogen-bonding interactions with lattice–water molecules of crystallization.