Magnetothermal Studies of a Series of Coordination Clusters Built from Ferromagnetically Coupled {(Mn4Mn6III)-Mn-II} Supertetrahedral Units.

Three high-nuclearity mixed valence manganese(II/III) coordination clusters, have been synthesised, that is, [(Mn6Mn4II)-Mn-III(mu(3)-O)(4)(HL1)(6)(mu(3)-N-3)(3)(mu(3)-Br)(Br)](N-3)(0.7)/(Br)(0.3)center dot 3MeCN center dot 2MeOH(1) (H3L1 = 3-methylpentan-1,3,5-triol), [(Mn11Mn6II)-Mn-III(mu(4)-O)(8)(mu(3)-Cl)(4)(mu,mu(3)-O2CMe)(2)(mu,mu-L-2)(10)Cl-2.34(O2CMe)(0.66)- (py)(3)(MeCN)(2)]center dot 7MeCN (2) (H2L2 = 2,2-dimethyl-1,3-propanediol and py is pyridine), and [(Mn12Mn7II)-Mn-III(mu(4)-O)(8)(mu(3)-eta N-1(3))(8)(HL3)(12)(MeCN)(6)]Cl-2 center dot 10MeOH center dot MeCN (3) (H3L3 = 2,6-bis(hydroxymethyl)-4-methylphenol) with high ground-spin states, S = 22, 28 +/- 1, and 83/2, respectively; their magnetothermal properties have been studied. The three compounds are based on a common supertetrahedral building block as seen in the Mn-10 cluster. This fundamental magnetic unit is made up of a tetrahedron of Mn-II ions with six Mn-III ions placed midway along each edge giving an inscribed octahedron. Thus, the fundamental building unit as represented by compound 1 can be described as a Mn-10 supertetrahedron. Compounds 2 and 3 correspond to two such units joined by a common edge or vertex, respectively, resulting in Mn-17 and Mn-19 coordination clusters. Magnetothermal studies reveal that all three compounds show interesting long-range magnetic ordering at low temperature, originating from negligible magnetic anisotropy of the compounds; compound 2 shows the largest magnetocaloric effect among the three compounds. This is as expected and can be attributed to the presence of a small magnetic anisotropy, and low-lying excited states in compound 2.