Journal of Inorganic and Organometallic Polymers and Materials

, Volume 23, Issue 2, pp 340–349

New host–guest supramolecular coordination polymers based on [(Me3Sn)3Fe(CN)6]n with alkali metal iodides and their applications as electrode materials in batteries

Authors

    • Department of Chemistry, Faculty of ScienceTanta University
  • Moustafa S. Ibrahim
    • Department of Chemistry, Faculty of ScienceTanta University
Article

DOI: 10.1007/s10904-012-9782-9

Cite this article as:
Etaiw, S.E.d.H. & Ibrahim, M.S. J Inorg Organomet Polym (2013) 23: 340. doi:10.1007/s10904-012-9782-9
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Abstract

The metal iodides reduce partially the host coordination polymer of the type \( ^{ 3}_{\infty } \left[ {\left( {{\text{Me}}_{ 3} {\text{Sn}}} \right)_{ 3} {\text{Fe}}\left( {\text{CN}} \right)_{ 6} } \right] \), I, to give new host–guest supramolecular coordination polymers (SCP). The physical and chemical characteristics of the new products were studied by elemental analyses, X-ray powder diffraction, IR, UV/Vis, and solid state NMR spectra. The host–guest SCP are [Mx(Me3Sn)3Fe(1–x)IIIFexII(CN)6]n M = Li+·2H2O, 1; Li+, 2; Na+, 3; K+, 4; Cu+, 5, [Li(Me3Sn)3FeII(CN)6]n, 6 and [(LiDEE)0.9(Me3Sn)3Feo.1IIIFeo.9II(CN)6]n, 7. The stoichiometry and nature of the guest depend on the type of the metal iodide and the reaction conditions. The polymeric nature of these SCP is due to the presence of trigonal bipyramidal configured structure which bridges between the single d-transition metal ions. The host–guest SCP containing the Li ions have been tested as electrodes to construct four different lithium-ion batteries.

Keywords

Supramolecular coordination polymersOrganotin polymersAlkali metalsHost–guest polymersLithium batteries

1 Introduction

Organotin (IV) compounds of the type R3SnX (R = alkyl and X-halide) react with hexacyano d-transition metal ions (Fe, Co,…) to form 3D-supramolecular coordination polymers [(R3Sn)mMd(CN)6]n (m = 3,4 and d = 3,2). The electronic and structure characterization of these SCP have been investigated [16]. Although single crystals of the strictly anhydrous SCP \( ^{ 3}_{\infty } \left[ {\left( {{\text{Me}}_{ 3} {\text{Sn}}} \right)_{ 3} {\text{Fe}}\left( {\text{CN}} \right)_{ 6} } \right] \) could not be obtained so far, its structure has been unambiguously deduced from detailed CPMAS solid state NMR and IR/Raman spectroscopic results and compared with the isostructure 3[(Me3Sn)3Co(CN)6] [46].These SCP are zeolite-like structure and form three dimensional networks in which up to one-third of the (Md–CN → M ← NC] chains are linear. The non-superimposable 3D-networks involve Me3Sn(NC)2 units of trigonal bipyramidal configuration and remarkably wide parallel channels with a diameter typically of 9.5 Å [7]. This novel mode of supramolecular architecture differs, however, from an initially envisaged [8], even less compact, super-Prussian blue (SPB) network which would involve a single type of strictly linear chains oriented along each of the three Cartesian axes. The availability of notably large cavities within these SCP and their oxidative properties have also been demonstrated chemically by the facile encapsulation of voluminous organic and organometallic guest cations into the negatively charged host lattice \( ^{ 3}_{\infty } \left[ {\left( {{\text{Me}}_{ 3} {\text{Sn}}} \right)_{ 3} {\text{Fe}}^{\text{II}} \left( {\text{CN}} \right)_{ 6} } \right]^{ - } \) formally accessible by complete or partial reduction of the iron homologue \( ^{ 3}_{\infty } \left[ {\left( {{\text{Me}}_{ 3} {\text{Sn}}} \right)_{ 3} {\text{Fe}}^{\text{III}} \left( {\text{CN}} \right)_{ 6} } \right] \) [918]. The presence of lithium-ion in the structure of the host–guest SCP leads to the possible use of these materials as electrodes in lithium ion secondary batteries. Many lithium-ion containing oxides are used as cathode materials for almost all commercial lithium-ion secondary batteries which are especially applied for mobile phones, personal computers, video-cameras, etc. due to the many advantages of the lithium secondary batteries [1926].

In this study, we report the solid state interaction of some metal halides as guest materials with the 3D-SCP [(Me3Sn)3FeIII(CN)6], I, to give new host–guest SCP, 17. The host attractive property of the SCP I was investigated to test its ability to be used as effective oxidizing reagent. The physical and chemical characteristics of the new host–guest SCP are studied by elemental analysis, X-ray powder diffraction, IR, UV/Vis, magnetic moment and solid state NMR spectra. The behavior of these host–guest SCP as electro-active electrodes in secondary batteries is, also, investigated.

2 Experimental details

All reagents used in this study were of a highly pure quality which were purchased from either Aldrich or Merck and used without further purification. FeOCl was prepared by the reaction of α-Fe2O3 with an excess of FeCl3 at 370 °C for one weak [27]. MoS2 was obtained from heating molybdenum trisulfide with hydrogen [28].

The SCP [(Me3Sn)3FeIII(CN)6], I, (M.W. = 703.18 g/mol) was prepared using the Schlenk-technique by adding aqueous solutions (10 ml) of 1 g. (5 mmol) of Me3SnCl and 0.55 g. (1.6 mmol) of K3[Fe(CN)6]. The product, I, was isolated, washed with water several times followed by diethylether (DEE) and dried under vacuum [6] (yield, 90 % with respect to K3[Fe(CN)6]). All the host–guest SCP, 17, had been prepared in a glove-box under anhydrous conditions and under nitrogen atmosphere with continuous grinding at room temperature. The host–guest SCP, 15, were prepared by adding the dry freshly prepared [(Me3Sn)3FeIII(CN)6], I, to a slight excess of the metal iodides (LiI·2H2O, LiI, NaI, KI and Cu2I2). 0.703 g. (1 mmol) of I was added to 0.509 g. (3 mmol) of LiI·2H2O, the product of 1 (M.W. = 741.74 g/mol) was quantitative. 0.703 g. (1 mmol) of I was added to 0.402 g. (3 mmol) of LiI, the product of 2 (M.W. = 709.34 g/mol) was quantitative. 0.703 g. (1 mmol) of I was added to 0.450 g. (3 mmol) of NaI, the product of 3 (M.W. = 723.83 g/mol) was quantitative. 0.703 g. (1 mmol) of I was added to 0.498 g. (3 mmol) of KI, the product of 4 (M.W. = 734.33 g/mol) was quantitative. 0.703 g. (1 mmol) of I was added to 0.573 g. (3 mmol) of Cu2I2, the product of 5 (M.W. = 754.33 g/mol) was quantitative. Also, the host–guest SCP 6 (M.W. = 710.03 g/mol), was prepared by adding 1 g. (1.42 mmol) of I to 0.053 g. (1.42 mmol) of lithium-tetrahydridoaluminate (LiAlH4) in DEE. The product was approximately quantitative. On the other hand, the addition of 0.501 g. (0.713 mmol) of I to an excess of lithium iodide, 0.509 g. (3 mmol), dissolved in 10 ml DEE yields the host–guest SCP, [(LiDEE)0.9 (Me3Sn)3 Fe0.1IIIFe0.9II(CN)6]n, 7. The products were isolated, washed with acetonitrile or acetone and dried under vacuum.

Microanalyses (C, H and N) were performed on the CHN–O Rapid from Heraues. The metal analysis was carried out by dissolving the substance in H2SO4/HNO3. The oxidation of organic groups by HNO3 was completed when NO-fumes no more appeared. After 1 h, the Sn was converted to the soluble SnCl2 salt by adding 5–10 ml of concentrated HCL which was heated slowly until the solution becomes very clear. Then after, the Sn was estimated photometrically with pyridyl-3-fluoron. The other metals were measured by Perkin-Elmer 5000 atomic absorption spectrophotometer. Infrared spectra were recorded on a Perkin-Elmer FT-IR-1720 spectrophotometer as KBr disc and/or Nujol mull in the range 4,000–400 cm−1. Raman Spectra were performed on Jobin–Yvon Ramanov U-1000 spectrophotometer. UV/Vis spectra were recorded on a Cary 5E from Varian as Nujol mull. Magnetic susceptibility was determined on Johnson Matthey susceptometer. X-ray diagrams were measured on Debye–Scherrer PW 1050 (Cux-Kα; Ni-filter) from Philips. CP/MAS solid state NMR spectra were carried out on Varian VXR-300. The solid-state NMR spectra were obtained at 30.40, 75.43, 79.34, 111.85 and 116.57 MHz using a Varian VXR-300 spectrometer in the cross-polarization mode with Doty scientific probes and high-power proton decoupling. For 15N and 13C 7-mm-0.d. rotors were employed, with typical MAS speeds in the range 4–5 kHz, whereas for 119Sn 5-mm-0.d. rotors with MAS rates of 10–13 kHz were generally used. In the case of the cross polarization stage, contact times in the range 1–10 ms and relaxation delays of 1–2 s were found to be appropriate. In general, many transients (10,000–60,000) were acquired for each spectrum, though for l3C this was only necessary to obtain good sensitivity for the cyanide carbon signals. Such sensitivity also required relatively high contact times.

Electrochemical behavior was studied by using the cell design which was made as two plates of cupper with a cavity covered by gold and has a radius of 0.65 cm and a surface area 1.326 cm2. The two electrodes contact through a cupper wire. The cell was constructed by placing two powder electro active intercalates on each side with filter paper separators socked in 1 M LiClO4 in propylene carbonate. Four types of cells were constructed:
$$ \begin{array}{*{20}c} {{\text{Cell }}\left( 1 \right)} \hfill & {\left[ {\left( {{\text{Me}}_{3} {\text{Sn}}} \right)_{3} {\text{Fe}}^{\text{III}} \left( {\text{CN}} \right)_{6} } \right]/ \, 1{\text{M LiClO}}_{4} {\text{in PC}}/{\text{ Li metal}}} \hfill \\ {{\text{Cell }}\left( 2 \right)} \hfill & {{{{{\left[ {\left[ {\left( {{\text{Me}}_{3} {\text{Sn}}} \right)_{3} {\text{Fe}}^{\text{III}} \left( {\text{CN}} \right)_{6} } \right]} \right]} \mathord{\left/ {\vphantom {{\left[ {\left[ {\left( {{\text{Me}}_{3} {\text{Sn}}} \right)_{3} {\text{Fe}}^{\text{III}} \left( {\text{CN}} \right)_{6} } \right]} \right]} {1{\text{M LiClO}}_{4} {\text{in PC}}}}} \right. \kern-0pt} {1{\text{M LiClO}}_{4} {\text{in PC}}}}} \mathord{\left/ {\vphantom {{{{\left[ {\left[ {\left( {{\text{Me}}_{3} {\text{Sn}}} \right)_{3} {\text{Fe}}^{\text{III}} \left( {\text{CN}} \right)_{6} } \right]} \right]} \mathord{\left/ {\vphantom {{\left[ {\left[ {\left( {{\text{Me}}_{3} {\text{Sn}}} \right)_{3} {\text{Fe}}^{\text{III}} \left( {\text{CN}} \right)_{6} } \right]} \right]} {1{\text{M LiClO}}_{4} {\text{in PC}}}}} \right. \kern-0pt} {1{\text{M LiClO}}_{4} {\text{in PC}}}}} {\left[ {{\text{Li}}_{0.9} \left( {{\text{Me}}_{3} {\text{Sn}}} \right)3{\text{Fe}}^{\text{II}}_{0.9} {\text{Fe}}^{\text{III}}_{0.1} \left( {\text{CN}} \right)_{6} } \right]}}} \right. \kern-0pt} {\left[ {{\text{Li}}_{0.9} \left( {{\text{Me}}_{3} {\text{Sn}}} \right)3{\text{Fe}}^{\text{II}}_{0.9} {\text{Fe}}^{\text{III}}_{0.1} \left( {\text{CN}} \right)_{6} } \right]}}} \hfill \\ {{\text{Cell }}\left( 3 \right)} \hfill & {{{{{\left[ {\left[ {\left( {{\text{Li}} \cdot 2{\text{H}}_{2} {\text{O}}} \right)_{0.9} \left( {{\text{Me}}_{3} {\text{Sn}}} \right)3{\text{Fe}}^{\text{II}}_{0.9} {\text{Fe}}^{\text{III}}_{0.1} \left( {\text{CN}} \right)_{6} } \right]} \right]} \mathord{\left/ {\vphantom {{\left[ {\left[ {\left( {{\text{Li}} \cdot 2{\text{H}}_{2} {\text{O}}} \right)_{0.9} \left( {{\text{Me}}_{3} {\text{Sn}}} \right)3{\text{Fe}}^{\text{II}}_{0.9} {\text{Fe}}^{\text{III}}_{0.1} \left( {\text{CN}} \right)_{6} } \right]} \right]} { 1 {\text{M LiClO}}_{4} {\text{in PC}}}}} \right. \kern-0pt} { 1 {\text{M LiClO}}_{4} {\text{in PC}}}}} \mathord{\left/ {\vphantom {{{{\left[ {\left[ {\left( {{\text{Li}} \cdot 2{\text{H}}_{2} {\text{O}}} \right)_{0.9} \left( {{\text{Me}}_{3} {\text{Sn}}} \right)3{\text{Fe}}^{\text{II}}_{0.9} {\text{Fe}}^{\text{III}}_{0.1} \left( {\text{CN}} \right)_{6} } \right]} \right]} \mathord{\left/ {\vphantom {{\left[ {\left[ {\left( {{\text{Li}} \cdot 2{\text{H}}_{2} {\text{O}}} \right)_{0.9} \left( {{\text{Me}}_{3} {\text{Sn}}} \right)3{\text{Fe}}^{\text{II}}_{0.9} {\text{Fe}}^{\text{III}}_{0.1} \left( {\text{CN}} \right)_{6} } \right]} \right]} { 1 {\text{M LiClO}}_{4} {\text{in PC}}}}} \right. \kern-0pt} { 1 {\text{M LiClO}}_{4} {\text{in PC}}}}} {\text{FeOCl}}}} \right. \kern-0pt} {\text{FeOCl}}}} \hfill \\ {{\text{Cell }}\left( 4 \right)} \hfill & {{{{{\left[ {\left[ {\left( {{\text{Li}} \cdot 2{\text{H}}_{2} {\text{O}}} \right)_{0.9} \left( {{\text{Me}}_{3} {\text{Sn}}} \right)3{\text{Fe}}^{\text{II}}_{0.9} {\text{Fe}}^{\text{III}}_{0.1} \left( {\text{CN}} \right)_{6} } \right]} \right]} \mathord{\left/ {\vphantom {{\left[ {\left[ {\left( {{\text{Li}} \cdot 2{\text{H}}_{2} {\text{O}}} \right)_{0.9} \left( {{\text{Me}}_{3} {\text{Sn}}} \right)3{\text{Fe}}^{\text{II}}_{0.9} {\text{Fe}}^{\text{III}}_{0.1} \left( {\text{CN}} \right)_{6} } \right]} \right]} {1{\text{M LiClO}}_{4} {\text{in PC}}}}} \right. \kern-0pt} {1{\text{M LiClO}}_{4} {\text{in PC}}}}} \mathord{\left/ {\vphantom {{{{\left[ {\left[ {\left( {{\text{Li}} \cdot 2{\text{H}}_{2} {\text{O}}} \right)_{0.9} \left( {{\text{Me}}_{3} {\text{Sn}}} \right)3{\text{Fe}}^{\text{II}}_{0.9} {\text{Fe}}^{\text{III}}_{0.1} \left( {\text{CN}} \right)_{6} } \right]} \right]} \mathord{\left/ {\vphantom {{\left[ {\left[ {\left( {{\text{Li}} \cdot 2{\text{H}}_{2} {\text{O}}} \right)_{0.9} \left( {{\text{Me}}_{3} {\text{Sn}}} \right)3{\text{Fe}}^{\text{II}}_{0.9} {\text{Fe}}^{\text{III}}_{0.1} \left( {\text{CN}} \right)_{6} } \right]} \right]} {1{\text{M LiClO}}_{4} {\text{in PC}}}}} \right. \kern-0pt} {1{\text{M LiClO}}_{4} {\text{in PC}}}}} {{\text{MoS}}_{2} }}} \right. \kern-0pt} {{\text{MoS}}_{2} }}} \hfill \\ \end{array} $$

All the electrochemical measurements were carried out using Multimeter Mavo 20 from Gossen. All the cells were activated by external load. The electrochemical data are related to materials properties, electrode concepts and test conditions [29, 30].

3 Results and discussion

3.1 Chemical properties and vibrational spectra

The metal iodides can reduce the SCP I partially to give new host–guest SCP, 17. The elemental analyses data, Table 1, of the SCP I and the prepared host–guest SCP, 17, after completeness of the reactions indicate that the guest cations are encapsulated within the cavities of the host SCP according to the following reactions:
Table 1

Structures and elemental analyses (found (clac.) %) for the SCP I and the host–guest SCP 17

No.

Composition of the SCP

C

H

N

Fe

Metal

I

[(Me3Sn)3FeIII(CN)6]n

25.52

(25.54)

3.87

(3.84)

11.80

(11.95)

7.92

(7.96)

 

1

[(Li.2H2O)0.9(Me3Sn)3IIFe0.9IIIFe0.1(CN)6]n

24.38

(24.27)

04.11

(04.13)

10.95

(11.30)

07.49

(07.55)

01.10

(00.93)

2

[(Li)0.9(Me3Sn)3IIFe0.9IIIFe0.1(CN)6]n

25.39

(25.38)

04.34

(03.81)

11.64

(11.84)

07.81

(07.89)

(00.97)

3

[(Na)0.9(Me3Sn)3IIFe0.9IIIFe0.1(CN)6]n

24.54

(24.86)

03.59

(03.73)

11.58

(11.60)

07.72

(07.74)

02.89

(03.18)

4

[(K)0.8(Me3Sn)3IIFe0.8IIIFe0.2(CN)6]n

24.27

(24.51)

03.68

(03.68)

11.35

(11.44)

07.52

(07.63)

04.07

(04.25)

5

[(Cu)0.8(Me3Sn)3IIFe0.8IIIFe0.2(CN)6]n

24.29

(23.86)

04.14

(03.58)

10.97

(11.14)

07.31

(07.42)

(06.79)

6

[Li(Me3Sn)3IIFe(CN)6]n

25.44

(25.35)

03.94

(03.80)

11.42

(11.83)

07.81

(07.80)

(00.98)

7

[(Li.DEE)0.9(Me3Sn)3IIFe0.9IIIFe0.1(CN)6]n

30.01

(29.60)

04.45

(04.72)

11.22

(10.94)

06.92

(07.14)

(07.14)

$$ \, \begin{array}{*{20}c} {\left[ {\left( {{\text{Me}}_{3} {\text{Sn}}} \right)_{3} {\text{Fe}}^{\text{III}} \left( {\text{CN}} \right)_{6} } \right]_{\text{n}} + } & {{\text{Xn MI}}\;{\underline{\text{grinding}}}\left[ {{\text{M}}_{\text{x}} \left( {{\text{Me}}_{3} {\text{Sn}}} \right)_{3} {\text{Fe}}^{\text{III}}_{{(1 - {\text{x}})}} {\text{Fe}}^{\text{II}}_{\text{x}} \left( {\text{CN}} \right)_{6} } \right]_{\text{n}} + {\text{ nx}}/2{\text{I}}_{2} } \\ {\text{I}} & {{\text{M}} = {\text{ Li}}^{ + } \cdot 2{\text{H}}_{2} {\text{O}},1;{\text{ Li}}^{ + } ,2;{\text{ Na}}^{ + } ,3;{\text{ K}}^{ + } ,4;{\text{ Cu}}^{ + } ,5.} \\ \end{array} $$
On the other hand, LiAlH4 reduced the SCP I completely to give one type of product 6:
$$ \begin{array}{*{20}c} {\left[ {\left( {{\text{Me}}_{3} {\text{Sn}}} \right)_{3} {\text{Fe}}^{\text{III}} \left( {\text{CN}} \right)_{6} } \right]_{\text{n}} + {\text{ n LiAlH}}_{4} \left( {\text{DEE}} \right) \, \to \, } & {\left[ {{\text{Li}}\left( {{\text{Me}}_{3} {\text{Sn}}} \right)_{3} {\text{Fe}}^{\text{II}} \left( {\text{CN}} \right)_{6} } \right]_{\text{n}} } \\ {\text{I}} & 6 \\ \end{array} $$
While the addition of dry freshly prepared I to an excess of lithium iodide dissolved in DEE yields the host–guest SCP 7.
$$ \begin{array}{*{20}c} {\left[ {\left( {{\text{Me}}_{3} {\text{Sn}}} \right)_{3} {\text{Fe}}^{\text{III}} \left( {\text{CN}} \right)_{6} } \right]_{\text{n}} + {\text{ n LiI }}\left( {\text{DEE}} \right) \, \to } & {\left[ {\left( {\text{LiDEE}} \right)_{0.9} \left( {{\text{Me}}_{3} {\text{Sn}}} \right)_{3} {\text{Fe}}^{\text{III}}_{0.1} {\text{Fe}}^{\text{II}}_{0.9} \left( {\text{CN}} \right)_{6} } \right]_{\text{n}} } \\ {\text{I}} & 7 \\ \end{array} $$

It is apparent from elemental analyses data that the amount of the guest metal cations incorporated in the cavities of the SCP I depends on the reducing property of the metal iodide. LiAlH4 was found to have the strongest reducing activity forming 6. KI and Cu2I2 are, relatively, weak reducing agents producing 4 and 5, respectively, which contain the least amount of the metal cations.

The IR spectrum of I displays the stretching vibrations of the cyanide groups as strong intensity bands at 2,155 and 2,148 cm−1 (Fig. 1). These cyanide wavenumbers are much higher than those in the original salt of the corresponding [FeIII(CN)6]−3 anion (i.e., υCN = 2,116 cm−1) suggesting the presence of \( {\text{FeCN}}\, \to \,{\text{Sn}} \) bridges. The band at 438 cm−1 due to \( \upsilon_{{{\text{Fe}}^{\text{III}} --{\text{C}}}} \) clearly reflects the presence of octahedral [FeIII(CN)6]−3 building blocks. The band at 554 cm−1 is due to the anti-symmetric stretching vibrations of the Sn–C bond while the υSn–N band appears at 419 cm−1. The absence of the symmetric stretching vibrations of the Sn–C bonds advocates the exclusive presence of trigonal planar R3Sn units owing to axial anchoring to two cyanide N atoms. On the other hand, the IR and Raman spectra of the new host–guest SCP 17 (Table 2; Fig. 1) exhibit strong IR bands at 2,017–2,078 cm−1 and medium bands in the region of 590–599 cm−1 corresponding to the stretching vibrations of the [FeII(CN)6]−4 building blocks [31, 32]. In addition the spectra of all host–guest SCP, except that of 6, display weak intensity bands at 244–440 cm−1 indicating the partial reduction of the [FeIII(CN)6]−3 building blocks to the FeII(CN)6 building blocks (Table 2). The υSn–N bands appear at 410–420 cm−1. On the other hand, the Raman spectra show intense bands at 2,050–2,096 cm−1 and weak intensity bands at 2,104–2,142 cm−1 supporting that the redox reaction \( \left[ {{\text{Fe}}^{\text{III}} \left( {\text{CN}} \right)_{ 6} } \right]^{ - 3} \, \to \, \left[ {{\text{Fe}}^{\text{II}} \left( {\text{CN}} \right)_{ 6} } \right]^{ - 4} \) has taken place. The presence of the various modes of vibrations of the trimethyltin groups (Table 2) indicates that these groups still play the role of linking the [Fe(CN)6] building blocks and act as connecting units to form the three dimensional network. The IR spectrum of 7 shows new bands at 1,200; 1,070; 1,031; 1,116 cm−1 due to the different modes of vibrations of DEE bonds.
https://static-content.springer.com/image/art%3A10.1007%2Fs10904-012-9782-9/MediaObjects/10904_2012_9782_Fig1_HTML.gif
Fig. 1

The IR-spectra of the SCP I and the host–guest SCP

Table 2

Infrared and Raman spectra for the SCP I and the host–guest SCP 17

Assignment

SCP I

1

2

3

4

5

6

7

\( \upsilon_{{{\text{Fe}}^{\text{II}} --{\text{CN}}}} \)

2,026; 2,047

2,078

2,046

2,077

2,075

2,051

2,067

2,070

2,075

2,017; 2,057

\( \upsilon_{{{\text{Fe}}^{\text{III}} --{\text{CN}}}} \)

2,145

2,139

2,139

2,140

2,140

2,114

2,133

\( \delta_{{{\text{Fe}}^{\text{II}} --{\text{C}}}} \)

 

594

596

591

596

599

593

590

υSn–C

547

552

550

553

552

553

553

551

υSn-N

420

417

418

420

415

420

413

410

υCH

2,915

2,925

2,919

2,918

2,919

2,920

2,924

2,924

δCH

1,404

1,598

1,462

1,462

1,462

1,462

1,460

γCH

792

793

791

792

791

788

790

789

υH2O

3,466

δH2O

 

1,639

      

υSn–C

523

520

523

522

522

 

522

523

(Raman)

550

  

553

    

υFeII-C

555

555

554

551

 

552

551

(Raman)

 

560

 

561

    

υFeII-CN

 

2,072;

2,050

2,073

2,069

 

2,050

2,072

(Raman)

 

2,088

2,096

2,075

    

υFeIII-CN

2,122

2,109; 2,117

2,118

2,104

2,136

 

2,116

(Raman)

2,150

2,133

2,142

2,106

    

3.2 X-ray powder diffraction

The X-ray powder diffraction supports the identity of the SCP I (Fig. 2). The experimental powder X-ray diffraction of SCP I is compared with the simulated pattern of the isostructure [(Me3Sn)3Co(CN)6] based on data resulting from X-ray structure analysis of single crystals [4]. The experimental and simulated diffractograms look very similar, suggesting that the final powdered bulk sample of SCP I is structurally closely related to the crystal structure of [(Me3Sn)3Co(CN)6]. A common feature of the structure is the presence of octahedral [Fe(CN)6] building blocks, which are continuously interlinked by practically planar R3Sn connecting units to form three infinite non-linear chains. The infinite channels result from the intersection of the Fe–CN–Sn(Me3)–NC–Fe chains, three of which define remarkably wide channels. The free open and wide channels allow encapsulation for in situ oxidation of the metal iodides to yield new host–guest SCP.
https://static-content.springer.com/image/art%3A10.1007%2Fs10904-012-9782-9/MediaObjects/10904_2012_9782_Fig2_HTML.gif
Fig. 2

The X-ray powder diffraction patterns for the SCP (I), the host–guest SCP (1) and (3) and the simulated X-ray diffraction [4] of [(Me3Sn)3Co(CN)6] (a)

The X-ray diffraction diagrams of the host–guest SCP 17 show the crystalline phase keeping with the probable polymeric nature of the materials. Figure 2 represents the X-ray diffractions of the host–guest SCP 1 and 3. The polymeric nature of these complexes is due to the presence of trigonal bipyramidal C=N–Sn–N=C– bridges between the single d-transition metal ions; Fe+n [46]. The difference in 2θ values between the SCP I and the host–guest SCP is due to the formation of new structure of the host–guest SCP which has different X-ray powder diffraction pattern than its homologue SCP I [7]. However, the crystalline phase was observed keeping with the probable polymeric nature of the host–guest SCP.

3.3 Electronic absorption spectra and magnetic moment

The UV/Vis spectrum of the host SCP I exhibits a band at 250 nm and a broad band at 390–440 nm (Fig. 3). These bands resemble those observed in K3[Fe(CN)6] where the first band corresponds to π–π* transitions from the metal to the cyanide ligand (\( {\text{M}}\, \to \,{\text{L}} \)) [33]. The low energy band at 400 nm is attributed to π–π* transitions of the [FeIII(CN)6] building blocks [18]. The UV/Vis spectrum of 6 exhibits a broad band around 325 nm corresponding to the π–π* transitions of the [FeII(CN)6] building blocks [16] accompanied by the disappearance of the band at 390–400 nm indicating complete reduction of FeIII to FeII. The spectra of the other host–guest SCP show two bands around 316 and 420 nm which can be considered as a further evidence of the partial reduction of the [FeIII(CN)6] building blocks (Table 3; Fig. 3). The UV/Vis spectrum of 5 displays a new absorption band at 483 nm due to intramolecular CT between CuI and FeIII.
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Fig. 3

The UV/Vis spectra of the SCP I and the host–guest SCP

Table 3

The electronic absorption spectra as Nujol mull matrix and the magnetic data for the SCP I and the host-gust SCP I7

No. of the host–guest SCP

λMax (nm)

μeff, B.M.

I

250, 390, 440

2.18

1

316, 418

0.51

2

318, 418

0.51

3

324, 416

0.42

4

320, 415

0.53

5

319, 410, 483

0.48

6

325

7

315, 420

0.61

The magnetic measurements of the 3D host–guest SCP support the IR and UV/Vis spectral data. In spite of I is paramagnetic with Meff = 2.18 B.M. due to low spin FeIII [14], the complex 6 is diamagnetic due to complete reduction of FeIII to FeII. The other host–guest SCP 15 and 7 exhibit low paramagnetic character (Table 3) due to the presence of both [FeII(CN)6] and [FeIII(CN)6] building blocks with different stoichiometric ratios in the 3D-networks.

3.4 Solid state NMR spectra of the host–guest SCP I and 3

The ambient temperature solid state 13C, 119Sn, 15N, 7Li, and 23Na CP/MAS NMR spectra of the host–guest SCP 1 and 3 have been examined as representative examples (Table 4; Figs. 4, 5, 6, 7). The 13C NMR spectrum of 1 in the methyl region exhibits three signals with practically different intensities, as is usual for trigonal bipyramidal structure of the zigzag chains (Fig. 4a). The three asymmetric signals may be due to rapid (on the NMR time scale) rotation of the Me3Sn fragments about their 3-fold N–Sn–N axes [6]. It is likely that either, there are effective three fold axes of symmetry along the N–Sn–N axes, or there is a rapid interchange of the methyl groups, in a given SnMe3 group by a novel type of internal rotation [32]. On the other hand, the 13C spectrum of 3 shows high intensity signal at 2.580 ppm (Fig. 4b) which indicates the presence of one crystallographic orientation in the distorted trigonal bipyramidal structure. The presence of only one 13C signal for neat Me3SnCN support the regular chains with rapidly rotating Me3Sn units [34]. The cyanide groups of 1 absorb at resonances 168.050, 173.835, 178.448 and 184.517 ppm, while 3 has δC resonances at 168.630, 170.168, 176.115 and 179.069 ppm (Table 4; Fig. 4). The four signals may result from the presence of four different CN groups in the unit cell or the more probable the splitting of two signals [35]. It is unbelievable that the splitting in the cyanide peaks arises from difference in the crystallographic sites in the unit structure. The splitting patterns might be expected to arise from coupling with the quadrupolar cyanide nitrogen and iron nuclei [35] (Fig. 4).
Table 4

CP/MAS solid state NMR resonances for the host–guest SCP 1 and 3 in ppm

No. of the SCP

13C (methyl)

13C (CN)

119Sn

15N

7Li, 23Na

1

−0.225

168.050

CP spectrum

 

2.283

173.835

  

−16.455,

 

6.087

178.448

  

−0.747

  

184.517

  

SP spectrum

     

−15.803,

     

−9.310,

     

−1.037

3

2.581

168.630

−108.933

−161.457

−5.011

  

170.168

45.080

−124.344

 
  

176.115

 

−109.403

 
  

179.069

   
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Fig. 4

75.430 MHz 13C NMR spectra of the host–guest SCP 1 (a) and 3 (b)

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Fig. 5

111.842 MHz 119Sn NMR spectrum of the host–guest SCP 3

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Fig. 6

116.573 MHz 7Li NMR spectrum of the host–guest SCP 1

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Fig. 7

79.341 MHz 23Na NMR spectrum of the host–guest SCP 3

The 119Sn CP/MAS solid state NMR spectrum of the host–guest SCP 3 exhibits two center bands at δSn resonances −108.933 and 45.08 ppm with a spinning side band manifold covering a range of ca. 400 ppm. The observation of only two signals indicates that the structural parameters of two less distorted Me3Sn(NC)2 units of the two chains are different from each other giving rise to two separated 119Sn resonances [36] (Fig. 5). On the other hand, the 119Sn CP/MAS solid state NMR spectrum of 1 was performed at 111.853 MHz and ambient temperature and recorded at low spin rates. However, the spectra are rather noisy and there is probably some overlapping of the signals. The spectrum was run at a spin rate of 13,100 Hz and has one clear manifold of spinning-side bands with the center band at −12.5 ppm.

The cross polarization 7Li NMR spectrum of the host–guest SCP 1 Shows one signal at δLi −0.747 ppm and a shoulder band on the right hand side whereas, the single pulse NMR spectrum shows three signals in the region from −15.803 to −1.037 ppm (Table 4; Fig. 6). The high frequency signal is slightly shifted and has a different line shape which might indicate two overlapping signals. The 7Li NMR spectra are not consistent with any mobility of Li+ cations along the internal channels of the network.

The 15N NMR spectrum for the host–guest SCP 3 shows three center bands of equal intensity (Table 4) which indicates the presence of three cyrstallographic different CN groups. The appearance of N of the polymeric chains between −109 and −170 ppm is characteristic of three coordinate “N” atoms in multiple bridging cyanide groups than the isocyanide ligand [37].

The 23Na NMR spectrum of 3 shows one signal at δNa −5.011 ppm (Table 4; Fig. 7) which is shifted more positive relative to the solid NaCl (δNa −11.00 ppm). This spectrum indicates a symmetric environment of Na+ cations in the lattic structure of the SCP 3. Valuable information about the structure of the host–guest SCP 1 and 3 are obtained from the solid state NMR results and the vibrational spectroscopy. The IR spectra of 1 and 3 in the υSn–C range show one band but the Raman active bands of the non-degenerate υSn–C vibrations show that the doubling may rather be due to the actual non-equivalence of the three methyl groups of each tin atom. On the other hand, there are two or three bands in the cyanide region of the IR spectra (i.e. around 2,000–2,200 cm−1), whereas, the 13C NMR spectra, in the cyanide region, exhibit four signals which have different intensities. The splitting of these bands indicates the presence of only three different crystallographic CN groups in the unit cell structure. This opinion was further supported by the cyanide 13C NMR spectra of [(Me3Sn)4Fe(CN)6] which display three equally intense cyanide center bands indicating the presence of three different CN groups in the asymmetric unit [37]. The 15N NMR spectrum of 3 indicates the presence of [FeII(CN)6]−4 building blocks with three crystallographic different CN groups. On the other hand, the IR spectrum of 3 shows two bands at 2,075 and 2,051 cm−1 due to the presence of two different CN groups in one chain. The presence of three different CN signals in the 15N NMR spectrum of 3 is further supported by the presence of two signals in the 119Sn NMR spectrum of 3. This observation would indicate the presence of two Me3Sn units in the structure having the same crystallography. The results of the spectra are evidence for the presence of [FeII(CN)6]−4 building blocks in the structure of 1 and 3. On the other hand, the observation of the δLi signals in the 7Li NMR spectrum of 1 and the high intensity signal in the 23Na spectrum of 3 at −5.011 ppm would then indicate the presence of Li and Na ions in the structure of 1 and 3, respectively.

3.5 Electrochemical behavior of the host–guest SCP in lithium cells

The presence of lithium ions as guest in the cavities of the 3D-SCP I encourages doing preliminary experiments to test their possible applications in the lithium-ion batteries. The behavior of the cells may be explained on the movement of lithium ions through the separator under the influence of potential and concentration gradients to the SCP or the electro active electrodes, whereas, the electron moved in the external circuit. After few cycles, this process becomes slow because no more Li+ cations are capable to leave the host–guest SCP and to structural modifications of the host–guest SCP. In the cell (1), the maximum output voltage is 3.29 volt, after the first cycle, the cell becomes poorly rechargeable because of the irreversible chemical and structure changes for both electrodes (Fig. 8). The problems in overall cell re-chargeability are mainly related to the lithium electrode as when it is exposed to moisture there is possibility of increasing temperature while the cell is corroding [26]. Also, the lithium in such solvents is always covered by peeled layer [38] which is an electronic insulator. Once the surface layer builds up to a thickness which prevents electron transfer across the cell, the cell loses its power, hence called discharge battery. Furthermore, the lithium anode was consumed in the charge–discharge processes and the SCP I, as a cathode, decomposes due to reaction with excess of lithium [39]. The main changes in the IR spectrum of the SCP I is the appearance of a band below 2,100 cm−1 due to the stretching vibrations of the [FeII(CN)6] bonds. The physical and chemical properties of the host–guest SCP containing Li+ cations in the cells (2), (3) and (4) during discharge are gathered from the color change from white to green [13] and change in the data of the elemental analysis. In addition, the IR spectra of the host–guest SCP after charge–discharge processes show the absence of bands above 2,100 cm−1 due to the complete reduction of the ferric ions to the ferrous ions. In reversible cells, the Li+ ions are rocked back and forth between the two intercalations. An ideal intercalation reaction involves the interstitial introduction of a guest species into a host compound without structural modification of the host. Such a reaction is reversible, but in an actual intercalation reaction, the bonding within the host may be slightly perturbed, for instance, a slight expansion of the structure may occur. The behavior of the cells (3) and (4) may be explained on the movement of lithium ions through the separator under the influence of potential and concentration gradients to the FeOCl or the MoS2 intercalates while the electrons are removed from FeOCl or MoS2 electrodes and transferred through the external circuit to the host–guest SCP. Some charge–discharge is obtained in few cycles after which the process becomes more difficult due to the un-ability of Li+ ions to remove the host–guest SCP. The relation between cell voltage and time for the cell (3) is illustrated in Fig. 9 which shows the discharge–charge characteristic between 0.50 and 0.10 V. The overall chargeability is encountered with some problems mainly related to the intercalated polymeric complexes. The behavior of the cells may be either reversible or irreversible depending on the specific nature of the structural changes of the host SCP.
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Fig. 8

Voltage–time curve for the cell (1) which contains 0.0414 g of the SCP I at the current density 4.5 A/cm2

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Fig. 9

Voltage–time curve for the cell (3) which contains 0.05 g of both electro-active materials at the current density 4.5 A/cm2

4 Conclusion

The availability of notably large cavities within the SCP I and its oxidative property have been utilized to synthesize host–guest SCP containing metal cations as guest. The stoichiometry of the host–guest SCP depends on the type of the metal iodide and reaction conditions. The presence of lithium as guest in the cavities of the 3D-SCP allows possible applications in the lithium batteries by using new cell design and electro-active electrodes such as Li metal, FeOCI and MoS2.

Acknowledgments

The authors are indebted to prof. Dr. R. D. Fischer (Hamburg University) for laboratory facilities and valuable discussions.

Copyright information

© Springer Science+Business Media New York 2012