Since the first lanthanide SMMs was discovered,1 lanthanide ions have become highly promising candidates for the development of SMMs because of their a large orbital angular momentum and high spin. It is well-known that β-diketones, a good bidentate chelating ligand, is not only able to sensitize the luminescence of lanthanide complexes,[2-10] but also afford SMMs.[11-14] Previously, the groups of Gao and Tang have reported the simple acetylacetonate (acac) dysprosium complexes with capping nitrogen auxiliary ligands, affording the highest effective energy barriers of 187 K for [Dy(acac)3(dppz)]·CH3OH.[15-16] Subsequently, some fluorine-containing β-diketones dysprosium SMMs were developed,[13,17-19] by way of adjusting the coordination geometry around the Dy(III) ions through the replacement of the auxiliary ligands. In the following we will focus on Er(III) complex, since the Er(III) SMMs has been less discussed and the Er(III) shows a ground J=15/2 state as the same as Dy(III), according to phenomenological approach popularized by Long, should behave differently in terms of the low temperature dynamics[20-21]. Recently, our group designed and synthesized a new β-diketone erbium complex, namely Er5(μ4-OH)(μ3-OH)4(μ-η2-Ph2acac)4(η2-DBM)6. Its crystal structure has been determined.

1 Experimental Section

1.1 Materials and instruments

Erium oxide (Er2O3, 99.99%) was purchased from Gan Zhou rare earth Chemical Plant (Jiang Xi, China). Other chemicals (98%, A. R.) were purchased from Shanghai D&R Finechem Co. (Shanghai, China). All chemicals except ErCl3·6H2O was obtained from commercial sources and used without further purification. ErCl3·6H2O was prepared by the reactions of Er2O3 and HCl in aqueous solution. Elemental (C and H) analyses were performed on a Perkin-Elmer 2400 analyzer. FT-IR spectra were collected on a Perkin-Elmer 100 spectrophotometer by using KBr pellets in the range of 4 000～450 cm-1. UV spectra were recorded on a Perkin-Elmer Lambda 35 spectrometer. Thermal analyses were carried out on a STA-6 000 analyzer with a heating rate of 10 ℃ min-1 in the range of 30～800 ℃ under a N2 atmosphere.

1.2 Er5(μ4-OH)(μ3-OH)4(μ-η2-Ph2acac)4(η2-DBM)6(1)

A solution of DBM (0.336 4 g, 1.5 mmol) and NaOH (0.060 0 g, 1.5 mmol) in 10 ml CH3OH were stirred half an hour, ErCl3·6H2O (0.188 5 g, 0.5 mmol) was added to the solution. The mixture was stirred for 24 h at room temperature. Single crystals suitable for XRD were obtained from toluene/petroleum ether within 5 or 7 days. Yield: 0.420 1 g (85.0%). Anal. Calcd for C55H41DyN2O6 (988.4): C, 66.83; H, 4.15; N, 2.83. Found: C, 66.80; H, 4.18; N, 2.85. IR (KBr, ν/cm-1): 3 433 (m), 1 601 (s), 1 553 (s), 1 514 (s), 1 413 (s), 1 313 (s), 1 218 (s), 1 071 (s), 721 (s), 604 (m). UV-Vis (CH3OH, λmax/nm): 253, 350.

通过比较5种森林类型步甲群落的多样性发现（表1），人工落叶松林中步甲物种多样性指数H'、优势度指数C和均匀度指数J均为最低，说明人工落叶松林步甲丰富度最低。天然林中不同林型步甲物种H'指数和C指数表现为次生白杨林>次生混交林>成熟混交林>成熟针叶林；J指数表现为次生混交林>成熟混交林>次生白杨林>成熟针叶林，说明成熟针叶林步甲物种多样性较其他天然林低。

“在下此生从无承诺，余生对他人许诺也会寥寥无几。”鬼算盘转移了话题，他道：“在下承诺：只要三少愿意接纳，在下会肝胆相照。”萧飞羽笑了，他道：“既然你肯定本庄只是侥幸，如此岂不是自寻死路？”鬼算盘从容地道：“原谅在下口出凶言：如果三少愿意，在下会倾力报效；如果三少意外，在下会马上觅地藏身。而且在下对藏身的法门颇有心得。”

1.3 X-ray crystallography

比较两组满意程度；微量泵注入胰岛素治疗的依从性、复常血糖的时间、住院治疗时间；护理前后血糖空腹指标、餐后2 h指标的监测结果；低血糖、酮症酸中毒等不良事件的发生率。

 

Table 1 Crystal data and structure refinement forcomplex 1

  

Complex1empiricalformulaC150H115Er5O25formulaweight313468colorbuffcrystsysttetragonalspacegroupP4/na/nm193750(5)b/nm193750(5)c/m，184371(6)α/(deg)90β/(deg)90γ/(deg)90V/nm369211(3)Z2ρ(gcm-3)1332μ(mm-1)2533F(000)3296Ra1，[I>2σ(I)]00652wRb1，[I>2σ(I)]01006Ra1，(alldata)01233wRb2，(alldate)00994GOFonF21123

2 Results and Discussion

2.1 Spectral analysis of complex 1

X-ray crystallographic analysis reveals that complex 1 crystallizes in the tetragonal space group P4/n, and the erbium atoms adopt the expected square-based pyramidal arrangement(Fig.3). Each triangular face of the square pyramid is capped by one μ3-O moiety. In the square-based face, four dysprosium atoms are linked by one μ4-O atom (from OH). A total of 10 peripheral ligands surround the Er5 cluster core. The ligand shows two different coordination modes. Six ligands are terminally chelating and four are bridging chelating, bonding to two metal ions that belong to the base of the polyhedron. The apical erbium, which lies on a 4-fold symmetry axis, is bonded to two disordered chelate ligands.

  

Scheme 1 Synthesis of complex 1

  

Fig.1 IR spectra (left) and UV absorption spectra (right) of DBM and complex 1

2.2 TG-DSC analysis of complex 1

TG-DSC analysis (Fig.2) for complex 1 is a single-step decomposition, meaning that there is no solvents in complex 1.

Single-crystal X-ray data of complex 1 was collected on an Oxford Xcalibur Gemini Ultra diffractometer with graphite-monochromated Mo Kα (λ = 0.710 73 nm) at room temperature. Empirical absorption corrections based on equivalent reflections were applied. The structure of complex 1 was solved by direct methods and refined by full-matrix least-squares methods on F2 using SHELXS-97 crystallographic software package[22]. All non-hydrogen atoms are anisotropically refined. All crystal data and structure refinement details for complex 1 is summarized in Table 1. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

  

Fig.2 TG-DSC curves of complex 1

2.3 Structural description of complex 1

Complex 1 was synthesized as shown in Scheme 1. The IR spectrum of ligand DBM exhibits the typical absorption of stretching frequencies of the hydroxyl in enol form (1 600 cm-1). However, the hydroxyl stretching frequency is shifted to lower wavenumbers in complex 1 (1 595 cm-1), which shows the involvement of the ligand DBM in the complex formation with Dy(III) ions (Fig.1, left). The UV-vis spectra show that there are obviously absorption bands around 341 nm for DBM and 350 nm for complex 1 (Fig.1, right), the absorption maxima is red-shifted 9 nm, which result from the singlet-singlet n-π* enol absorption of the β-diketonate.

  

Fig.3 Local coordination geometry of Er(III) ion for complex 1

3 Conclusion

In summary, the reaction of 1 equiv of ErCl3 ·6H2O with 3 equiv of dibenzoylmethane in the presence of NaOH yields the pentanuclear dysprosium hydroxy cluster of composition Er5(μ4-OH)(μ3-OH)4(μ-η2-Ph2acac)4(η2-DBM)6. Isolation of a DBM erbium lanthanide complex 1 verifies that the DBM ligand is able to co-stabilize the Er(III) ion forming square-based pyramidal arrangement.

4 Acknowledgements

This work is financially supported by the National Natural Science Foundation of China (No. 21601132); Heilongjiang College Student Innovation and Entrepreneurship Training Program Project (No. 201710236028); Suihua Science and Technology Plan Project (No. SHKJ 2017-073)

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