English

• 1. INTRODUCTION

  In the latest decade, metallochalcogenides have attracted great attention owing to their peculiar attributes, such as luminescence, semiconduction, ion-exchange, magnetism, and uranium removal^[1-10]. For instance, ZnIn₂S₄^[11] and oxidized SnS₂^[12] sheets exhibit high-efficiency carbon dioxide (CO₂) reduction performances under visible-light illumination. Among them, unlike dense and bulky phase materials as three-dimensional CdS or layered MoS₂, open-framework chalcogenidometalates, mainly constructed from supertetra-hedral clusters (denoted as Tn, Cn, Pn, Tp, q, OTn and so on by Feng et al.)^[13], have unique cooperative effects combining absorption-based capture, optoelectronic nature, and quantum-dot structure, which could lead to new applications and currently are being intensively investigated^{[14, 15]}. Up to now, a huge number of supertetrahedral metallochalcogenides and their open-frameworks have been obtained. However, to our knowledge, quite few organometal chalcogenides were reported^{[16, 17]}. Herein, we have attained linear {Butyl-Sn₄S₈} tetramer, which could serve as linker to coordinate with two metal complexes (Mn-TEPA or Ni-TEPA, where TEPA = tetraethylenepentamine), constructing a ribbon-like hexameric structure ((butyl-Sn)₄S₈M₂(TEPA)₂, denoted as 1 and 2, when M = Mn and Ni, respectively). Magnetic measurements were conducted to show that both 1 and 2 show ferromagnetic-like behavior, with the Weiss (θ) values and the intradimer coupling constants (J) up to 8.5 K and 6.8 cm^-1 for 1 and 21.1 K and 17.2 cm^-1 for 2, respectively.

  2. EXPERIMENTAL

  2.1 Materials and instruments

  All reagents were obtained from commercial sources and used without further purification. Elemental analyses (EA) for C, H, and N were carried out on a German Elementary Vario EL III instrument. Infrared (IR) spectra were collected on a PerkinElmer spectrometer with KBr pellets (range, 500~4000 cm^-1). Ultraviolet-visible (UV-Vis) diffuse reflection spectra (DRS) were recorded on a PerkinElmer Lamda-950 UV spectrophotometer with BaSO₄ substrates (range, 200~800 nm). Energy dispersive X-ray (EDX) spectra were acquired by a JSM-6700F scanning electron microscope. Thermogravimetric analyses (TGA) were measured on a NETZSCH STA 449F5 thermal analyzer under N₂ atmosphere (range, 30~800 ℃; heating rate, 10 ℃∙min^-1). Powder X-ray diffraction (PXRD) data were performed on a Rigaku miniFlex II diffractometer with Cu-Kα (λ = 1.54056 Å) in the 2θ range of 3~50° (scan speed, 1 °∙min^-1). Variable-temperature and field-dependent magnetization data were conducted on a Quantum Design MPMS-XL magnetometer (temperature range, 2~300 K; magnetic field range, 0~50 kOe; experimental susceptibilities were corrected for the diamagnetism of the constituent atoms by use of Pascal's tables).

  2.2 Syntheses of 1-(butyl-Sn)₄S₈Mn₂ and 2-(butyl-Sn)₄S₈Ni₂

  1-(butyl-Sn)₄S₈Mn₂ (TEPA)₂ was synthesized from solvothermal method by adding methanol (MeOH, 2 mL), n-butylSnCl₃ (50 μL) and tetraethylenepentamine (TEPA, 2.5 mL) into a mixture of Mn(OAc)₂·4H₂O (221.2 mg, 0.91 mmol) and sulfur (S, 32 mg, 1 mmol) in a 20 mL vial, and heated to 80 ℃ for 7 days. Light-yellow block-shaped crystals were collected after cooling to room in ca. 43% yield based on S. EA data for C₃₂H₈₂N₁₀S₈Sn₄Mn₂ (1): Calcd. (%): C, 26.57; H, 4.46; N, 9.69. Found (%): C, 26.55; H, 5.53; N, 9.66. IR (KBr, cm^-1): 3290(m), 3224(m), 3162(m), 2952(m), 2908(m), 2854(m), 2349(w), 2160(w), 2096(w), 1963(w), 1660(m), 1581(m), 1458(m), 1365(m), 1286(m), 1242(m), 1207(m), 1174(m), 1116(m), 1085(m), 995(s), 939(s), 871(m), 821(m), 682(m), 574(m), 493(s).

  2-(butyl-Sn)₄S₈Ni₂(TEPA)₂ was synthesized from solvother-mal method by adding distilled water (2 mL), n-butylSnCl₃ (50 μL) and TEPA (2.5 mL) into a mixture of Ni(OAc)₂·4H₂O (223.1 mg, 0.91 mmol) and sulfur (S, 33.1 mg, 1 mmol) in a 20 mL vial and heated to 80 ℃ for 7 days. Light-purple block-shaped crystals were collected after cooling to room in ca. 57% yield based on S. EA data for C₃₂H₈₂N₁₀S₈Sn₄Ni₂ (2): Calcd. (%): C, 25.88; H, 4.31; N, 9.74. Found (%): C, 26.37; H, 5.73; N, 9.60. IR (KBr, cm^-1): 3332(m), 3245(m), 3157(m), 3120(m), 2948(m), 2898(m), 2852(m), 1714(w), 1629(m), 1579(m), 1456(m), 1373(m), 1340(m), 1286(m), 1243(m), 1143(m), 1083(m), 1054(m), 1008(m), 941(s), 881(m), 767(m), 678(m), 563(m), 486(m), 422(m).

  2.3 X-ray crystallography

  Single crystals of suitable size were selected and mounted on a glass fiber. Single-crystal X-ray diffraction (SCXRD) data were collected on a Rigaku Saturn724+ diffractometer equipped with graphite-monochromatized Mo-Kα radiation (λ = 0.71073 Å) at 298 K. Absorption corrections by the multi-scan method were applied. The structures were solved by direct methods with SHELXS-97 program and refined on F² by full-matrix least-squares methods using SHELXL-2014 program package embedded in OLEX2. All non-hydrogen atoms were located with successive difference Fourier technique and refined anisotropically. Hydrogen atoms were added in the idealized positions and refined with isotropic parameters. The final R = 0.0629, wR = 0.1285 for 12855 observed reflections (I > 2σ(I), w = 1/[σ²(F_o²) + (0.0333P)² + 0.0412P], where P = (F_o² + 2F_c²)/3), S = 1.001, (Δ/σ)_max = 0.001, (Δρ)_max = 1.63 and (Δρ)_min = –0.88 e·Å^-3 for 1-(butyl-Sn)₄S₈Mn₂. The final R = 0.0464, wR = 0.1185 for 9267 observed reflections (I > 2σ(I), w = 1/[σ²(F_o²) + (0.0333P)² + 0.0412P], where P = (F_o² + 2F_c²)/3), S = 1.017, (Δ/σ)_max = 0.001, (Δρ)_max = 1.19 and (Δρ)_min = –0.87 e·Å^-3 for 2-(butyl-Sn)₄S₈Ni₂. Selected bond lengths and bond angles from X-ray structure analyses are listed in Table S2~S5 (SI).

  3. RESULTS AND DISCUSSION

  3.1 Crystal structures of 1-(butyl-Sn)₄S₈Mn₂ and 2-(butyl-Sn)₄S₈Ni₂

  SCXRD analyses revealed that both compounds 1 and 2 crystallize in the triclinic P$ \overline 1 $ space group, and possess the same building units of hexamer {(Butyl-Sn)₄S₈(M-TEPA)₂} (M = Mn for 1, and Ni for 2). In each asymmetric unit, there are four bridged S^2- linkers, one [Mn-TEPA]²⁺ and two [butyl-Sn]³⁺ moieties. Ligands of TEPA are not deprotonated during the self-assembly process. Sn1 and Sn2 adopt different coordination modes: Sn1 links to three μ₂-S^2- atoms and one butyl group, while Sn2 bonds four μ₂-S^2- atoms and one butyl group. As shown in Figs. 1 and 2, the paramagnetic-ions Mn²⁺ and Ni²⁺ are coordinated by one μ₂-S^2- atom and five N atoms from a same TEPA amine in a distorted octahedron of coordination geometry. Two [M-TEPA]²⁺ complexes are connected via long chain of [Sn₄S₈] to form a hexamer {(Butyl-Sn)₄S₈(M-TEPA)₂} (M = Mn for 1, and Ni for 2), with the distances between terminal transition metals to be 13.485 and 14.078 Å for 1 and 2, respectively. However, complexes 1 and 2 possess different packing fashions through hydrogen bonding interactions (N–H⋅⋅⋅S) (Fig. 1b and 2b, Figs. S1 and S2 in SI), which are in the ranges of 2.438~2.479 Å for 1 and 2.410~2.545 Å for 2, respectively.

  Figure 1

  

  Figure 1.  (a) Crystal structure and polyhedral drawing of compound 1-(butyl-Sn)₄S₈Mn₂; (b) Hydrogen-bonding interaction of 1; (c) Packing mode of 1 along with [100] direction. Hydrogen atoms were omitted for clarity in a and c

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  Figure 2

  

  Figure 2.  (a) Crystal structure and polyhedral drawing of compound 2-(butyl-Sn)₄S₈Ni₂; (b) Hydrogen-bonding interaction of 2; (c) Packing mode of 2 along with [010] direction. Hydrogen atoms were omitted for clarity in a and c

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  3.2 Characterization (PXRD, TGA, UV-Vis, FT-IR, EDX)

  Confirmed by PXRD (Fig. 3a and 4a), we can conclude that phase purities of 1-(butyl-Sn)₄S₈Mn₂ and 2-(butyl-Sn)₄S₈Ni₂ are quite good since the experimental patterns match well with the simulated ones. As shown in Fig. 3b and 4b, structures 1 and 2 could be stable up to 200 ℃ under N₂ atmosphere. Calculated by the extrapolation of the linear part of [Ahv]² plot of the transformed Kubelka-Munk spectra in Fig. 3c and 4c, their band gaps are 3.097 and 3.325 eV for 1 and 2, respectively. From the FT-IR spectra collected in Fig. 3d and 4d, all the significant peaks could be attributable to the stretching vibration of TEPA, butyl, and the related solvents. EDX spectroscopy was also used to testify the chemical composition of 1 and 2, as shown in Fig. 5.

  Figure 3

  

  Figure 3.  Powder XRD patterns (a), TGA plot (b), FT-IR spectrum (c), and transformed Kubelka-Munk UV-Vis spectrum (d) of compound 1-(butyl-Sn)₄S₈Mn₂

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  Figure 4

  

  Figure 4.  Powder XRD patterns (a); TGA plot (b); FT-IR spectrum (c); and transformed Kubelka-Munk UV-Vis spectrum (d) of compound 2-(butyl-Sn)₄S₈Ni₂

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  Figure 5

  

  Figure 5.  EDX spectra of compounds (a) 1-(butyl-Sn)₄S₈Ni₂; and (b) 2-(butyl-Sn)₄S₈Ni₂

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  3.3 Magnetic properties

  The temperature dependences of the magnetic susceptibility of 1-(butyl-Sn)₄S₈Mn₂ and 2-(butyl-Sn)₄S₈Ni₂ in the 2~300 K temperature range are plotted in Fig. 6. For 1, the experiment χ_MT value at 300 K is 8.29 cm³∙K∙mol^-1, close to the spin-only value (8.75 cm³∙K∙mol^-1, S = 5/2) expected for two isolated Mn²⁺ ions. As the temperature is lowered, χ_MT value first increases smoothly to 8.74 cm³∙K∙mol^-1 at 48 K, indicating a dominant ferromagnetic interaction of the Mn²⁺ ions, then decreases down to 6.54 cm³∙K∙mol^-1 at 2 K. The reciprocal susceptibility χ_M^-1 vs. temperature curve above 50 K obeys the Curie-Weiss law, with the Curie value (C) of 8.15 cm³∙K∙mol^-1 and Weiss constant (θ) being 8.5 K, indicating an overall ferromagnetic behavior in 1. Sample 2 exhibits the same magnetic phenomenon as 1. The χ_MT value at 300 K is 1.93 cm³∙K∙mol^-1, which is also close to the spin-only value (2.00 cm³∙K∙mol^-1, S = 1) expected for two isolated Ni²⁺ ions. As the temperature is lowered, the χ_MT value first rises to 2.22 cm³∙K∙mol^-1 at 36 K, and then drops upon further cooling. In addition, its C and θ values were calculated to be 1.87 cm³∙K∙mol^-1 and 21.1 K, respectively. Based on the structural feature, the magnetic susceptibility data of 1 and 2 could be analyzed by using a dinuclear model (isotropic Hamiltonian equation of Ĥ = –2JS_A∙S_B, where J is for the intradimer coupling constant), in which the contribution of the intermolecular interaction (zJ') is also taken into account. The least-squares fitting of the magnetic susceptibility data gives the following parameters: J = 6.8(7) cm^–1, zJ' = –0.3(5) cm^–1, g = 2.02(3) and R = 1.5 × 10^–4 for 1; J = 17.2(8) cm^–1, zJ' = –0.8(4) cm^–1, g = 2.07(4) and R = 2.1 × 10^–4 for 2, respectively. These values further confirm the ferromagnetic interaction character between the Mn²⁺ or Ni²⁺ ions via the tetrameric {butyl-Sn₄S₈} bridges.

  Figure 6

  

  Figure 6.  Magnetic properties of compounds 1-{Mn₂} (a) and 2-{Ni₂} (b): Temperature dependence of the χ_MT product (red scatter, where the black line represents the isotropic Hamiltonian fitting), and the χ_M^-1 vs. T (blue scatter, where the black line represents the Curie-Weiss fitting) with inset of the magnetization curve

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  4. CONCLUSION

  In summary, we report herein the synthesis, structure and magnetic properties of two organotin-sulfide-spaced dimers {Mn₂} (1) and {Ni₂} (2) terminated by TEPA. Both 1 and 2 feature similar structures of tetrameric {butyl-Sn₄S₈}, which further connects two Mn-TEPA (1) or Ni-TEPA complexes (2), respectively. Notably, complexes 1 and 2 exhibit an overall ferromagnetic-like behavior.

  
  
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• 

  Figure 1  (a) Crystal structure and polyhedral drawing of compound 1-(butyl-Sn)₄S₈Mn₂; (b) Hydrogen-bonding interaction of 1; (c) Packing mode of 1 along with [100] direction. Hydrogen atoms were omitted for clarity in a and c

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  Figure 2  (a) Crystal structure and polyhedral drawing of compound 2-(butyl-Sn)₄S₈Ni₂; (b) Hydrogen-bonding interaction of 2; (c) Packing mode of 2 along with [010] direction. Hydrogen atoms were omitted for clarity in a and c

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  Figure 3  Powder XRD patterns (a), TGA plot (b), FT-IR spectrum (c), and transformed Kubelka-Munk UV-Vis spectrum (d) of compound 1-(butyl-Sn)₄S₈Mn₂

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  Figure 4  Powder XRD patterns (a); TGA plot (b); FT-IR spectrum (c); and transformed Kubelka-Munk UV-Vis spectrum (d) of compound 2-(butyl-Sn)₄S₈Ni₂

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  Figure 5  EDX spectra of compounds (a) 1-(butyl-Sn)₄S₈Ni₂; and (b) 2-(butyl-Sn)₄S₈Ni₂

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  Figure 6  Magnetic properties of compounds 1-{Mn₂} (a) and 2-{Ni₂} (b): Temperature dependence of the χ_MT product (red scatter, where the black line represents the isotropic Hamiltonian fitting), and the χ_M^-1 vs. T (blue scatter, where the black line represents the Curie-Weiss fitting) with inset of the magnetization curve

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