Two Decanuclear DyIIIxCoII10-x (x = 2, 4) Nanoclusters: Structure, Assembly Mechanism, and Magnetic Properties.

ABSTRACT

The aggregation and formation of heterometallic nanoclusters usually involves a variety of complex self-assembly processes; thus, the exploration of their assembly mechanisms through process tracking is more challenging than that for homometallic nanoclusters. We explored here the effect of solvent on the formation of heterometallic clusters, which gave two heterometallic nanoclusters, [Dy2Co8(µ3-OCH3)2(L)4(HL)2(OAc)2(NO3)2(CH3CN)2]·CH3CN·H2O (1) and [Dy4Co6(L)4(HL)2(OAc)6(OCH2CH2OH)2(HOCH2CH2OH)(H2O)]·9CH3CN (2), with the H3L ligand formed from the in situ condensation reaction of 3-amino-1,2-propanediol with 2-hydroxy-1-naphthaldehyde in the presence of Co(OAc)2·4H2O and Dy(NO)3·6H2O. It is worth noting that the skeleton of cluster 1 has a high stability under high-resolution electrospray ionization mass spectrometry (HRESI-MS) conditions with a gradually increasing energy of the ion source. Cluster 2 underwent a multistep fragmentation even under a zero ion-source voltage for the measurement of HRESI-MS. Further analysis showed that cluster 2 underwent a possible fragmentation mechanism of Dy4Co6L6 → Dy2Co6L5/DyL → DyCo2L3/DyCo2L → DyL/Co2L2. Most notably, the species emerging in the formation process of cluster 1 were tracked using time-dependent HRESI-MS, from which we proposed its possible formation mechanism of H2L → Co2L2 → Co2DyL2/Co3L2 → Co3DyL2 → Co4DyL2 → Co5Dy2L4 → Co8Dy2L6. As far as we know, it is the first time to track the formation process of Dy-Co heterometallic clusters through HRESI-MS with the proposed assembly mechanism. The magnetic properties of the two titled DyIIIxCoII10-x (x = 2, 4) clusters were studied. Both of them exhibit slow magnetic relaxation, and 1 is a single-molecule magnet at zero direct-current field.