Giant Heterometallic [Mn36Ni4]0/2- and [Mn32Co8] "Loops-of-Loops-and-Supertetrahedra" Molecular Aggregates.

ABSTRACT: We report the synthesis, crystal structures and magnetic properties of the giant heterometallic [Mn36Ni4]2-/0 (compounds 1, 2)/[Mn32Co8] (compound 3) "loops-of-loops-and-supertetrahedra" molecular aggregates and of a [Mn2Ni6]2+ compound (cation of 4) that is structurally related with the cation co-crystallizing with the anion of 1. In particular, after the initial preparation and characterization of compound [Mn2Ni6(?4-O)2(?3-OH)3(?3-Cl)3(O2CCH3)6(py)8]2+[Mn36Ni4(?4-O)8(?3-O)4(?3-Cl)8Cl4(O2CCH3)26(pd)24(py)4]2- (1) we targeted the isolation of (i) both the cationic and the anionic aggregates of 1 in a discrete form and (ii) the Mn/Co analog of [Mn36Ni4]2- aggregate. Our synthetic efforts toward these directions afforded the discrete [Mn36Ni4] "loops-of-loops-and-supertetrahedra" aggregate [Mn36Ni4(?4-O)8(?3-O)4(?3-Cl)8Cl2(O2CCH3)26(pd)24(py)4(H2O)2] (2), the heterometallic Mn/Co analog [Mn32Co8(?4-O)8(?3-O)4(?3-Cl)8Cl2(?2-OCH2CH3)2(O2CCH3)28(pd)22(py)6] (3) and the discrete [Mn2Ni6]2+ cation [Mn2Ni6(?4-O)2(?3-OH)4(?3-Cl)2(O2CCH3)6(py)8](ClO4)(OH) (4). The structure of 1 consists of a mixed valence [ Mn28III Mn8II Ni4II ]2- molecular aggregate that contains two Mn8III Ni2II loops separated by two Mn6III Mn4II supertetrahedral units and a [ Mn2III Ni6II ]2+ cation based on two [MnIII Ni3II (?4-O)(?3-OH)1.5(?3-Cl)1.5]4+ cubane sub-units connected through both mono- and tri-atomic bridges provided by the ?4-O2- and carboxylate anions. The structures of 2-4 are related to those of the compounds co-crystallized in 1 exhibiting however some differences that shall be discussed in detail in the manuscript. Magnetism studies revealed the presence of dominant ferromagnetic interactions in 1-3 that lead to large ground state spin (ST) values for the "loops-of-loops-and-supertetrahedra" aggregates and antiferromagnetic exchange interactions in 4 that lead to a low (and possibly zero) ST value. In particular, dc and ac magnetic susceptibility studies revealed that the discrete [Mn36Ni4] aggregate exhibits a large ST value ~ 26 but is not a new SMM. The ac magnetic susceptibility studies of the [Mn32Co8] analog revealed an extremely weak beginning of an out-of-phase tail indicating the presence of a very small relaxation barrier assignable to the anisotropic Co2+ions and a resulting out-of-phase ac signal whose peak is at very low T.

SUBMITTER: Charalambous M 

PROVIDER: S-EPMC6413240 | biostudies-literature | 2019

REPOSITORIES: biostudies-literature