Structure and assembly studies of two planar Dy(<sc>iii</sc>) single molecule magnets with double relaxations

A systematic understanding of the assembly mechanism of single-molecule magnets (SMMs) is of great significance for the directional synthesis of Dy(iii) SMMs as well as improving SMM performance. Herein, we present the interesting formation mechanisms of two new single molecule magnets [Dy-4(mu(3)-OH)(2)(L-1)(4)(L ')(2)]<middle dot>5CH(3)CN (1, HL ' = 5-bromo-2-hydroxybenzaldehyde) and [Dy-6(mu(3)-OH)(2)(L-2)(2)(HL2)(2)(H2L2)(2)Cl-2(EtOH)(2)]Cl-2<middle dot>4MeOH<middle dot>2CH(3)CN<middle dot>4H(2)O (2) featuring planar Dy-4 and Dy-6 skeletons fused from two- and four edge-sharing triangular Dy-3 units, respectively, which were obtained from the reactions of N,N '-bis(5-bromo-2-hydroxybenzylidene)-2-dimethylpropane-1,3-diamine (H2L1) with Dy(NO)(3)<middle dot>6H(2)O and 2-[(5-bromo-2-hydroxy-benzylidene)-amino]-2-hydroxymethyl-propane-1,3-diol (H4L2) with DyCl3<middle dot>6H(2)O, respectively. Another eye-catching feature is that both 1 and 2 are zero-field SMMs with rarely reported double relaxations. The third interesting feature is that the intermediates formed in the reaction courses of 1 and 2 were tracked using time-dependent high resolution electrospray ionization mass spectrometry (HRESI-MS), which helped to propose a step-by-step assembly mechanism of (H2L1 + Dy -> Dy(L-1) -> Dy-2(L-1)(2) -> Dy-2(L-1)(3) -> Dy-3(L-1)(3) -> Dy-4(L-1)(3) -> Dy-4(L-1)(4) -> Dy-4(L-1)(4)(L ')(2)) for 1 and (H4L2 + Dy -> Dy-2(L-2) -> Dy-2(L-2)(3) -> Dy-3(L-2)(4) -> Dy-6(L-2)(6)) for 2.