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We obtained a binuclear Gd(III) complex [Gd2(L1)2(NO3)4] (1, HL1 = (E)-2-(2-(pyridin-2-ylmethyleneamino)ethoxy)ethanol) by reacting N2O2-tetradentate chelating ligand HL1 with Gd(NO3)3·6H2O at solvothermal temperature of 100 °C. Time-dependent high-resolution electrospray ionization mass spectrometry (HRESI-MS) followed the formation of 1 and revealed it's the assembly mechanism: HL1 → Gd(L1) → Gd2(L1)2. When we used the NO2-tridentate chelating ligand HL2 (HL2 = 2-(2-aminoethoxy)ethanol) under the same reaction conditions, we obtained an "hourglass-like" nonanuclear Gd(III) cluster [Gd9(L2)8(μ3-OH)8(μ4-O)2(NO3)8]·2CH3OH·H2O (2). Their assembly mechanism was proposed: HL2 → Gd(L2) → Gd2(L2)2 → Gd3(L2)3 → Gd4(L2)4 → Gd5(L2)4 → Gd9(L2)8. Most notably, when we used the NO-bidentate chelate ligand HL3 (HL3 = picolinic acid), we obtained a dodecanuclear Gd(III) cluster [Gd12(L3)8(OH)16(NO3)8(OH)4(H2O)4]·22CH3OH·25CH3CN (3) under the same reaction conditions. We found that the formation process of cluster 3 involved two different and mutually interfering self-assembly processes, namely, multitemplate-induced assembly (HL3 → Gd(L3) → Gd2(L3)2 → Gd12(L3)8) and stepwise assembly (HL3 → Gd(L3) → Gd2(L3)2 → Gd3(L3)2 → Gd4(L3)2 → Gd5(L3)2 → Gd6(L3)2 → Gd12(L3)8). [ABSTRACT FROM AUTHOR]

The formation of high-nuclearity clusters of lanthanide usually involves many complicated self-assembly processes. Thus, tracking the formation process is extremely difficult and research on the assembly mechanism is very rare. In this study, a Dy-exclusive nanocluster containing vertex-sharing [Dy4(μ3-OH)4] cubanes, denoted as [Dy12(L)8(OH)16(CH3O)8(H2O)8]·(CH3O)4 (Dy12, L = quinoline-2-carboxylate), was designed and synthesized from L and DyCl3·6H2O. Eight quinoline-2-carboxylate ligands were encapsulated on the periphery of the Dy12 cluster, which served to stabilize the core. The high stability of the Dy12 cluster core was further confirmed by high-resolution electrospray-ionization mass spectrometry (HRESI-MS). With increased ion-source energy, only CH3O− and OH− bridging ligands were replaced inside the Dy12 cluster. Notably, eight intermediate fragments were successfully observed from the Dy12 cluster formation by time-dependent HRESI-MS. First, ligand L captured Dy3+ to give Dy1, which further formed Dy2 through μ2-O bridging. The Dy12 cluster was constructed in one step with four Dy2 and four Dy3+ as templates: L → Dy1→ Dy2→ Dy12. Moreover, a series of Dy3–Dy6 fragment peaks with relatively weak intensities were observed, and an alternative stepwise-assembly route was proposed: L → Dy1→ Dy2→ Dy3→ Dy4→ Dy5→ Dy6→ Dy12. On comparing the two different assembly methods, the multitemplate guided assembly formed Dy12 was found to be dominant. To the best of our knowledge, this study was the first to propose the involvement of two self-assembly mechanisms in the construction of lanthanide clusters, as further confirmed by HRESI-MS. Magnetic studies further showed that Dy12 clusters exhibited field-induced single-molecule magnet behavior. [ABSTRACT FROM AUTHOR]

Two polymorphs of supramolecular isomers, a discrete dimer and a zig-zag chain, having the same chemical composition, [Mn(Hbit)Cl2] (Hbit=1-methyl-2-(1H-1,2,3-triazol-4-yl)-1H-benzo[d]imidazole), were obtained solvothermally in a one-pot synthesis. The isomers differ in a number of ways: orange blocks versus pale-yellow needles, triclinic P1 versus orthorhombic Pbcn, double µ2-Cl versus alternate single and triple µ2-Cl, coordination number 5 versus 6, and antiparallel versus parallel near-neighbor orientation of Hbit. The packing in each case is driven by the supramolecular interactions, H-bonds (N--H…Cl, C--H…Cl) and π…π overlaps, calculated to be in the range 20-36 kcalmol-1. Calculations gave a difference of only 2 kcalmol-1 in favor of the dimer, which confirms with the observation of principally the dimer at short reaction time. ESI-MS spectra of the dissolved crystals reveal the same fragments with similar distributions. The presence of two fragments at m/z 286.96 [MnIV(Hbit)Cl-2H]+ and 323.94 [MnIII (Hbit)Cl2]+ indicates that [Mn(Hbit)Cl2] is the building unit in both cases; thus, the different orientations of the ligands lead to the two polymorphs stabilized by the respective supramolecular interactions. Importantly, the chain form represents the first example with alternate single and triple µ2-Cl bridges. The magnetic interactions are weakly antiferromagnetic in both cases, with J in the range 0.07-0.34 cm-1; however, high-field EPR analysis reveals moderate magneto-anisotropy with D=0.26(1) cm-1, E=0.06(1) cm-1 and D=0.17(1) cm-1, E=0.03(1) cm-1, respectively. [ABSTRACT FROM AUTHOR]