Self-assembly of [Cu(CN)4]3− ions with cationic {Me3Sn}+ or {Me2Sn(CH2)3SnMe2}2+ fragments in the presence of a nBu4N+ template

doi:10.1016/S0022-328X(00)00747-6

Journal of Organometallic Chemistry

Volume 621, Issues 1–2, 1 March 2001, Pages 254-260

Dedicated to Professor H. Brunner on the occasion of his 65th birthday

https://doi.org/10.1016/S0022-328X(00)00747-6 Get rights and content

Abstract

As described earlier, solutions of ⁿBu₄NCl and K₃[Cu(CN)₄] react with Et₃SnCl to zeolite-like [(Bu₄N)(Et₃Sn)₂Cu(CN)₄] (1), but with Me₃SnCl exclusively to [(Bu₄N)(Me₃Sn)Cu₂(CN)₄] (2), the crystal structure of which is reported here for the first time. The ⁿBu₄N⁺ guest ions of 2 are accommodated between planar, negatively charged layers, wherein three-coordinated Cu(I) ions are interlinked by CN and CN·SnMe₃·NC bridges (2:1). The slightly modified new homologue of 2: [(ⁿBu₄N){Me₂Sn(CH₂)₃SnMe₂}_0.5Cu₂(CN)₄] (3), displays an almost identical powder X-ray diffractogram as 2 and, moreover, surprisingly similar solid-state NMR spectra for the nuclei ¹³C, ¹⁵N and ¹¹⁹Sn. A three-dimensional host framework is postulated to encapsulate the ⁿBu₄N⁺ guest of 3, the Sn atoms of adjacent layers being therein tied pair-wise together by trimethylene tethers, (CH₂)₃. For further comparison, the solid-state NMR data of the new coordination polymer [{Me₂Sn(CH₂)₃SnMe₂}_0.5Au(CN)₂] (5) are also presented.

Introduction

Super-Prussian blue [1] derivatives of the organometallic family [(R₃E)₃M^III(CN)₆] $^{∧}$ $^{3} ∞$ [M^IIIμ-{CNE(R₃)NC}₃] with R=alkyl, E=Sn or Pb and M=Fe, Co, Rh or Ir [2] still resemble the familiar Prussian blue representatives $^{3} ∞$ [Mμ-(CN)₃] (usually with M=0.5 M′+0.5 M′′) [3] structurally, although their intra-chain M⋯M separations are about twice as large (i.e. of ca. one nm) as in classical Prussian blue systems. Replacement of the octahedral M(CN)₆ by tetrahedral M(CN)₄ building blocks would lead to coordination polymers more closely related to zeolites. While numerous zeolite-like polymeric metal cyanides involving the ‘classical’ MCNM′ bridge, and usually a guest cation, G⁺, are known, [4], [5] the coordination polymer [(ⁿBu₄N)(Et₃Sn)₂Cu(CN)₄] (1), is still unique in displaying the expanded MCNSnR₃NCM bridge [6]. In spite of extensive attempts to prepare, and characterize, further examples of the general type [G(R₃E)₂Cu(CN)₄], only too reluctantly crystallizing products either of the desired composition or of a quite unexpected new type, [G(R₃E)Cu₂(CN)₄], have so far been described [6], [7]. Single crystals suitable to determine the crystal structure of the longest known [6] representative of this latter class, [(ⁿBu₄N)(Me₃Sn)Cu₂(CN)₄] (2), could be obtained only most recently. In the present contribution, the supramolecular architecture of 2 will be presented and correlated with extended multinuclear solid-state NMR results. The slightly modified, new product [(ⁿBu₄N){Me₂Sn(CH₂)₃SnMe₂}_0.5Cu₂(CN)₄] (3), which differs from 2 formally in that two methyl groups of each pair of Me₃Sn units are replaced by one (CH₂)₃ spacer, is also characterized both by its solid-state NMR spectra and its powder X-ray diffractogram (XRD). In view of convincing experimental evidence in favor of a practically isostructural architecture of 2 and 3, a plausible proposal for the location of the trimethylene tether in the structure of 3 is likewise possible.

Section snippets

Preparation of 2 and 3

Both [(ⁿBu₄N)(Me₃Sn)Cu₂(CN)₄] (2) [6] and [(ⁿBu₄N){Me₂Sn(CH₂)₃SnMe₂}_0.5Cu₂(CN)₄] (3) were obtained first (as so-called derailment products) when the synthesis of potential zeolite-like homologues of 1 containing tin-bonded alkyl ligands of lower space demand than required by ethyl groups was attempted: $2 Me_{3} SnCl (or ClMe_{2} Sn (CH_{2})_{3} SnMe_{2} Cl)+ K_{3} [Cu (CN)_{4}]+^{n} Bu_{4} NCl→3KCl +[(^{n} Bu_{4} N)(Me_{2} SnR)_{2} Cu (CN)_{4}] (R = Me or (CH_{2})_{3/2})$

However, according to the C/H/N and metal analyses, which reflected constantly a Sn:Cu ratio

Crystal structure of 2

For the negatively charged [(Me₃Sn)Cu₂(CN)₄⁻] host framework of 2, three different structural motifs might in principle be envisaged. One of them could involve just one tetracoordinate Cu(I) center which might build up, in combination with the two potential, rod-like tethers {CNCuNC}⁻ and {CNSnMe₃NC}⁻, either a quasi-diamondoid framework (3-D) or puckered layers (2-D) of the composition [Cu{μ-CNCuNC}{μ-CNSn(Me₃)NC}]. The second motif could involve no longer unusual [11] {Cu₂(μ₃-CN)₂} fragments,

Powder X-ray diffractometry of 2 and 3

In Fig. 4, the experimental powder X-ray diffractograms (XRD's) of 2 and 3 are compared with the simulated XRD of 2, the latter being based on data resulting from the structure analysis of a single crystal (vide supra). All three XRD's look very similar, suggesting immediately that the finely powdered bulk samples of both 2 and 3 should at least be structurally closely related to crystalline 2. It should be noted here that usually the lighter atoms of a sample containing heavier metal atoms

CPMAS solid-state magnetic resonance spectra of 2 and 3

The chemical shifts of all resonances of the nuclei ¹³C, ¹⁵N and ¹¹⁹Sn are, as far as detectable in the solid-state NMR spectra of 2 and 3, listed for comparison in Table 4. Both 2 and 3 give rise to only one ¹¹⁹Sn center band, in spite of the notable disorder of the tin atoms as reflected by the single-crystal X-ray study of 2. Correspondingly, just one singlet is found for the tin-bonded methyl carbon atoms of 2, most probably owing to rapid rotation of the Me₃Sn group about its NSnN axis

Conclusions

Although the quality of the crystal structure analysis of 2 might be somewhat affected by the significant disorder of the tin and carbon atoms of the Me₃Sn unit, any severe doubts in the supramolecular architecture based on that stucture analysis can be rejected in accounting also for the detailed solid-state NMR studies of 2 and 3. Owing to almost identical powder X-ray diffractograms (Fig. 4), both compounds are practically isostructural and display, consequently, for the nuclei ¹³C, ¹⁵N and

Experimental

To avoid CO₂ uptake, all preparative work was carried out under an atmosphere of dry nitrogen. Compound 2 was synthesized as reported earlier [6]. Micocrystalline 2 containing in a few cases also some single crystals large enough to be used for an X-ray study grew from the mother liquors obtained after the spontaneous precipitation of comparatively little bulk material, filtration and deposition of the solution at a temperature of ca. 20°C for several weeks.

For the preparation of 3, a clear

Supplementary data

Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic Data Center, CCDC No. 150095 for compound 2. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge CB2 1EC, UK (Fax: +44-1223-336033; e-mail: [email protected] or www: http://www.ccdc.cam.ac.uk).

Note added in proof

Most recently, the new compound [ⁿBu₄NCu₃(CN)₄]MeCN has been shown to be almost isostructural with 2, in that each MeSn fragment of 2 is replaced by a two-coordinate Cu(I) spacer [21].

Acknowledgements

This work was supported by the Deutsche Forschungsgemeinschaft (Joint Project: Nano-porous crystals). The CP MAS NMR work was supported by the UK EPSRC (through the National Solid-State Magnetic Resonance Service based at Durham). We also thank Dr F. Olbrich (Otto-von-Guericke-Universität Magdeburg) for collecting the X-ray data set and Mrs S. Samba for her involvement in the successful preparation of single crystals of 2.

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Self-assembly of [Cu(CN)4]3− ions with cationic {Me3Sn}+ or {Me2Sn(CH2)3SnMe2}2+ fragments in the presence of a nBu4N+ template

Abstract

Introduction

Section snippets

Preparation of 2 and 3

Crystal structure of 2

Powder X-ray diffractometry of 2 and 3

CPMAS solid-state magnetic resonance spectra of 2 and 3

Conclusions

Experimental

Supplementary data

Note added in proof

Acknowledgements

J. Organomet. Chem.

J. Organomet. Chem.

Solid State Ionics

Spectrochim. Acta Part A

J. Organomet. Chem.

Chem. Eur. J.

Organometallics

Progr. Inorg. Chem.

Self-assembly of [Cu(CN)₄]³⁻ ions with cationic {Me₃Sn}⁺ or {Me₂Sn(CH₂)₃SnMe₂}²⁺ fragments in the presence of a ⁿBu₄N⁺ template