Thermally Stable Terbium(II) and Dysprosium(II) Bis-amidinate Complexes.

The thermostable four-coordinate divalent lanthanide (Ln) bis-amidinate complexes [Ln(Piso)2] (Ln = Tb, Dy; Piso = {(NDipp)2CtBu}, Dipp = C6H3iPr2-2,6) were prepared by the reduction of parent five-coordinate Ln(III) precursors [Ln(Piso)2I] (Ln = Tb, Dy) with KC8; halide abstraction of [Ln(Piso)2I] with [H(SiEt3)2][B(C6F5)] gave the respective Ln(III) complexes [Ln(Piso)2][B(C6F5)]. All complexes were characterized by X-ray diffraction, ICP-MS, elemental analysis, SQUID magnetometry, UV-vis-NIR, ATR-IR, NMR, and EPR spectroscopy and ab initio CASSCF-SO calculations. These data consistently show that [Ln(Piso)2] formally exhibit Ln(II) centers with 4fn5dz21 (Ln = Tb, n = 8; Dy, n = 9) valence electron configurations. We show that simple assignments of the f-d coupling to either L-S or J-s schemes are an oversimplification, especially in the presence of significant crystal field splitting. The coordination geometry of [Ln(Piso)2] is intermediate between square planar and tetrahedral. Projecting from the quaternary carbon atoms of the CN2 ligand backbones shows near-linear C···Ln···C arrangements. This results in strong axial ligand fields to give effective energy barriers to magnetic reversal of 1920(91) K for the Tb(II) analogue and 1964(48) K for Dy(II), the highest values observed for mononuclear Ln(II) single-molecule magnets, eclipsing 1738 K for [Tb(C5iPr5)2]. We tentatively attribute the fast zero-field magnetic relaxation for these complexes at low temperatures to transverse fields, resulting in considerable mixing of mJ states.

Tetraanionic arachno-Carboranyl Ligand Imparts Strong Axiality to Terbium(III) Single-Molecule Magnets.

A family of fully sandwiched arachno-lanthanacarborane complexes formulated as {η6 -[µ-1,2-[o-C6 H4 (CH2 )2 ]-1,2-C2 B10 H10 ]2 Ln}{Li5 (THF)10 } (Ln=Tb, Dy, Ho, Er, Y) is successfully synthesized, where the "carbons-adjacent" carboranyl ligand (arachno-R2 -C2 B10 H10 4- ) bears four negative charges and coordinates to the central lanthanide ions using the hexagonal η6 C2 B4 face. Thus, the central lanthanide cations are pseudo-twelve-coordinate and have an approximate pseudo-D6h symmetry or hexagonal-prismatic geometry. As the crystal field effect imparted by this geometry is still unknown, we thoroughly investigated the magnetic properties of this series of complexes and found that the crystal field imposed by this ligand causes a relation of Tb>Dy>Ho>Er for the energy gaps between the ground and the first excited states, which is of striking resemblance to the ferrocenophane and phthalocyanine ligands although the latter two ligands give disparate local coordination geometries. Moreover, the effective energy barrier to magnetization reversal of 445(10) K, the observable hysteresis loop up to 4 K and the relaxation time of the yttrium-diluted sample reaching 193(17) seconds at 2 K under an optimized field for the Tb analogue of this family of arachno-lanthanacarborane complexes, render a new benchmark for Tb3+ -based single-molecule magnets.

[Market survey of Caryophylli Flos specifications].

The present study aimed to regulate the market circulation of Caryophylli Flos and formulate standards for commodity specifications and grades of Caryophylli Flos. Market survey was carried out in four major medicinal material markets with 48 samples of Caryophylli Flos collected. The property, 100-seed weight, impurity percentage, moisture, and eugenol content in Caryophylli Flos of different specifications from different producing areas were determined and analyzed. The results showed that 27.1% of the samples surveyed on the markets did not meet the requirements of Chinese Pharmacopoeia(2020 edition). The 100-seed weight and the property are important factors for the classification of Caryophylli Flos specifications. There were significant differences in the property, 100-seed weight, impurity percentage, and eugenol content in Caryophylli Flos samples of different specifications from different producing areas, and also differences in the proportions of different specifications in Caryophylli Flos samples from different producing areas. The African-originated Xiaohong(medium grade) and Guangxi-originated Xiaohong(medium grade) accounted for 70% and 66.7% respectively, the Indonesian-originated Dahong(top grade) for 56.2%. In conclusion, there are many problems in the circulation of Caryophylli Flos at present, mainly including the loss of origin information, no standards for specifications, non-implementation of grade standards, excessive impurities, and no evidence for authenticity identification. According to the classification of Caryophylli Flos specifications in this study, the average eugenol content of Xiaohong is significantly higher than the Dahong by 4.74%.

The Gigantic {Ni36Gd102} Hexagon: A Sulfate-Templated "Star-of-David" for Photocatalytic CO2 Reduction and Magnetic Cooling.

Gigantic coordination molecules assembled from a large number of metal ions and organic ligands are structurally and functionally challenging to characterize. Here we show that a heterometallic cluster [Ni36Gd102(OH)132(mmt)18(dmpa)18(H2dmpa)24(CH3COO)84(SO4)18(NO3)18(H2O)30]·Br6(NO3)6·(H2O)x·(CH3OH)y, (1, x ≈ 130, y ≈ 60), shaped like a "Star of David", can be synthesized using a "mixed-ligand" and "sulfate-template" strategy. In terms of metal nuclearity number, 1 is the second largest 3d-4f cluster to date. In the solid state, 1 is porous after removing the lattice guests. The N2 adsoption experiment reveals that the BET and Langmuir surface areas are 299.8 and 412.0 cm2 g-1, respectively. CO2 adsorption at 298 K gives the amount of 45 cm3 g-1 for 1. More importantly, 1 is soluble in common organic solvents and exhibits high solution stability revealed by high resolution MALDI-TOF mass spectroscopy, small-angle X-ray scattering (SAXS), and low-dose transmission electron microscopy. The solubility and the potential open metal sites owing to the labile coordinating components prompted us to investigate the photocatalytic properties of 1, which displays high selectivity and efficiency for reduction of CO2 to CO with turnover number and turnover frequency of 29700 and 1.2 s-1, respectively. These values are higher than most catalysts working under the same conditions, presumably due to the strong Ni-CO2 binding effect. In addition, the large percentage of Gd(III) in 1 leads to a large magnetic entropy change (41.3 J·kg-1·K-1) at 2.0 K for ΔH = 7 T.

Dysprosiacarboranes as Organometallic Single-Molecule Magnets.

The dicarbollide ion, nido-C2 B9 H11 2- is isoelectronic with cyclopentadienyl. Herein, we make dysprosiacarboranes, namely [(C2 B9 H11 )2 Ln(THF)2 ][Na(THF)5 ] (Ln=Dy, 1Dy) and [(THF)3 (µ-H)3 Li]2 [{η5 -C6 H4 (CH2 )2 C2 B9 H9 }Dy{η2 :η5 -C6 H4 (CH2 )2 C2 B9 H9 }2 Li] 3Dy and show that dicarbollide ligands impose strong magnetic axiality on the central DyIII ion. The effective energy barrier (Ueff ) for the loss of magnetization can be varied by the substitution pattern on the dicarbollide. This finding is demonstrated by comparing complexes of nido-C2 B9 H11 2- and nido-[o-xylylene-C2 B9 H9 ]2- , which show a Ueff of 430(5) K and 804(7) K, respectively. The blocking temperature defined by the open hysteresis temperature of 3Dy reaches 6.8 K. Moreover, the linear complex [Dy(C2 B9 H11 )2 ]- is predicted to have comparable properties with the linear [Dy(CpMe3 )2 ]+ complex. As such, carboranyl ligands and their derivatives may provide a new type of organometallic ligand for high-performance single-molecule magnets.

Desolvation-Degree-Induced Structural Dynamics in a Rigid Cerium-Organic Framework Exhibiting Tandem Purification of Ethylene from Acetylene and Ethane.

Due to the industrial requirements for high production and high quality of ethylene, efficient purification of ethylene from acetylene and ethane is of prime importance but challenging. Dynamic metal-organic frameworks (MOFs) have demonstrated intriguing structural dynamics and diverse applications recently. Among them, although a few flexible ones have exhibited interesting ethylene purification capability, rigid ones were yet barely investigated for such purpose. In this regard, a cerium(III)-based MOF was solvothermally synthesized, which is rigid and assembled from rod molecular building blocks associated with coordinative N,N-dimethylformamide (DMF) molecules. After liberating different degrees of DMF ligands via heating under vacuum or acetone exchange, both partially desolvated compounds of Ce-MOF-1 and Ce-MOF-2 were concertedly isolated in a fashion of single-crystal to single-crystal transformation. Although both newly generated materials crystallize in the same space group, they exhibit dissimilar unit cell parameters and slightly distinct ultramicropore sizes and pore microenvironments, thanks to the discrepancy in the desolvation degree. Consequently, Ce-MOF-1 and Ce-MOF-2 individually demonstrate C2H2- and C2H6-selective adsorption behavior, resulting in the potential tandem separation of C2H4 from C2H2 and C2H6 mixtures. The above results were successfully supported by not only single gas adsorption isotherms but also grand canonical Monte Carlo (GCMC) calculation studies and dynamic breakthrough experiments. The present work may pave the way for rigid MOFs aiming at advancing applications via solid-state structural dynamics.

A study of cation-dependent inverse hydrogen bonds and magnetic exchange-couplings in lanthanacarborane complexes.

Ten lanthanacarborane complexes were synthesized to study the rare B-Hδ-∙∙∙Mn+ inverse hydrogen bonds (IHBs). The average bonding energy of B-Hδ-∙∙∙Ln3+ is theoretically determined to be larger than 24 kJ/mol, which is comparable to moderately strong hydrogen bonds (21-56 kJ/mol). In addition to NMR and IR, magnetometer was used to study the exchange-coupling interaction via such B-Hδ-∙∙∙Ln3+ IHBs in detail, and the coupling constant is determined to be -2.0 cm-1, which is strong enough to compare with single-atom bridged dysprosium(III) complexes. Two imidazolin-iminato incorporated complexes have shown energy barrier for magnetization reversal larger than 1000 K, and the exchange-biasing effects are evident. Moreover, the bonding strengths of B-Hδ-∙∙∙Mn+ IHBs are cation-dependent. If M = Na, the B-Hδ-∙∙∙Na+ bonding energy is reduced to 14 kJ/mol, and the dimerization process is no longer reversible. The exchange-biasing effect is also disappeared. We believe such a finding extends our knowledge of IHBs.