Insights into the Coordination Ability of Siloxanes Employing Partially

Feb 21, 2019 - Insights into the Coordination Ability of Siloxanes Employing Partially Silicon Based Crown Ethers: A Comparative Analysis of s-Block M...
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Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

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Insights into the Coordination Ability of Siloxanes Employing Partially Silicon Based Crown Ethers: A Comparative Analysis of s‑Block Metal Complexes Fabian Dankert and Carsten von Hänisch*

Inorg. Chem. Downloaded from pubs.acs.org by WEBSTER UNIV on 02/21/19. For personal use only.

Fachbereich Chemie and Wissenschaftliches Zentrum für Materialwissenschaften (WZMW), Philipps-Universität Marburg, Hans-Meerwein-Straße 4, 35043 Marburg, Germany ABSTRACT: Herein we present the synthesis and coordination chemistry of the partially silicon based crown ether analogues 1,2,4,5-tetrasila-benzo[15]crown-5 (1) and 1,2,4,5-tetrasila[18]crown-6 (7). Stable complexes of alkali and alkaline earth metal iodides could be obtained showing the good coordination ability of these ligands. The complexes [MA(1,2,4,5-tetrasila-benzo[15]crown-5)I] (MA = Li+ (2), Na+ (4)) and [MEA(1,2,4,5-tetrasila-benzo[15]crown-5)I2] (MEA = Mg2+ (3), Ca2+ (5), Sr2+ (6)) were obtained by equimolar reaction of 1 with the respective alkali or alkaline earth metal iodide. Depending on the ionic radii of the respective cations, the coordination modes of the siloxane backbone are significantly different and could be well-represented by means of 29Si NMR spectroscopy. In addition, we were able to generate the unusual dinuclear complex [Ba2(1,2,4,5-tetrasila[18]crown-6)2I4] (8) by reaction of 7 with BaI2. All compounds were characterized via single crystal X-ray diffraction (XRD) analysis.

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INTRODUCTION The silicon analogues of crown ethers and cryptands opened a new chapter in host−guest chemistry, and the imitation of organic analogues can help to understand the Si−O bond, especially regarding the Lewis basicity of silicon affected oxygen atoms.1 The Lewis basicity of siloxane compounds has been intensely discussed over the past years, but all considerations of the Si−O bond conclude a lower basicity of the oxygen atoms in comparison to those bonds in carbon related systems. On one hand, negative hyperconjugation interactions are discussed. These occur in especially permethylated systems and are, in this context, understood as a donation of electron density in this case p(O) → σ*(Si−C). A subsequent coordination to a metal center is hindered due to a competing polarization.2,3 On the other hand, the Si−O bond is considered highly ionic. This causes spatially diffuse electron pairs.4 Furthermore, repulsive interactions between the positively polarized silicon atoms and a Lewis acid occur. Both effects are disadvantageous in terms of complex formation.5,6 With the insertion of Si2Me4 units rather than SiMe2 units into a residual C2H4O framework (see Scheme 1b,c), we could demonstrate that these effects have to be taken into account but low basicity also originates from different architecture of cyclosiloxanes in comparison to crown ethers (Scheme 1a). Crown ethers bearing a single disilane unit readily form stable complexes with alkali and alkaline earth metal salts, and the coordination ability is comparable to that of the purely organic crown ethers which is confirmed by means of NMR experiments and DFT calculations.7−10 Furthermore, even hydrogen bonding could be established as the incorporation of ammonium cations was realized.12 Very recently new insights into the Si−O bond were given as ligands © XXXX American Chemical Society

Scheme 1. Binding Modes of Crown Ethers (a) and Disilanyl-Bearing Crown Ethers (b−d): (b) Hybrid Crown Ethers Bearing a Single Disilane Unit,7−10 (c) Hybrid Crown Ethers Bearing Disilane Units Opposite Each Other,7 and (d) Hybrid Crown Ethers Bearing Two Adjacent Disilane Units9,11,a

a Curves represent different organic spacers. See cited works for further information.

bearing a single O−Si−Si−O linkage were found to be effective for the incorporation of exclusively hard cations. Negative hyperconjugation interactions in these disilanebearing systems are easily overcompensated when a hard group 1 or 2 metal ion is coordinated. The harder the cation is, the higher the impact is on the siloxane linkage, and a higher bonding energy is the outcome.13,14 Especially group 2 metal ions seem to readily form stable complexes with ligands bearing a Si−O moiety.13,15,16 The group of Harder very recently introduced the synthesis and structure of the Received: January 11, 2019

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DOI: 10.1021/acs.inorgchem.9b00086 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry fascinating magnesium complex [Mg(BDI){O(SiMe3)2}]+ (BDI = CH[C(CH3)N-Dipp]2 where Dipp = 2,6-diisopropylphenyl) and demonstrated unsupported silyl ether coordination by means of XRD and 29Si NMR experiments.17 While the coordination chemistry of ligands bearing a single O−Si−Si− O linkage has advanced quite well, the coordination chemistry of ligands bearing two or more adjacent disilane units (see Scheme 1d) is at an early stage. With [Li(1,2,4,5-tetrasila[12]crown-4)OTf] (OTf = CF3SO3−) only one example is known so far in which the uncommon binding motif (Si2Me4)2O···LA (LA = Lewis acid) could be observed.11 The ligand shows a fair complexation ability, but additional experimental data is necessary in order to understand the coordination chemistry of a ligand with the O−Si2Me4−O−Si2Me4−O moiety. We herein report on novel s-block coordination compounds representing the uncommon binding motif (Si2Me4)2O···LA. The influence of different Lewis acids toward the siloxane linkage is discussed by means of single crystal X-ray diffraction analysis and 29Si NMR chemical shift.

Figure 1. Molecular structure of 2 in the crystal. Thermal ellipsoids represent the 50% probability level. Hydrogen atoms and solvent molecules of benzene are omitted for clarity. Only one out of four independent molecules per asymmetric unit is shown. Selected bond lengths [pm]: O1−Li1 227.6(15), O2−Li1 201.6(14), O3−Li1 227.6(15), O4−Li1 203.1(16), O5···Li1 451.8(1), I1−Li1 273.1(15). Selected bond angles [deg]: O1−Li1−O2 105.0(6), O2−Li1−O3 72.5(5), O3−Li1−O4 75.4(5), Si2−O5−Si3 147.9(5).

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RESULTS AND DISCUSSION In past works we were able to generate 1,2,4,5-tetrasila[12]crown-4 and 1,2,4,5-tetrasila[18]crown-6.9,11 In this work we aimed to synthesize a tetrasila-crown ether with a size between these two ligands. 1,2,4,5-Tetrasila-benzo[15]crown-5 (1) is accessible by reaction of the corresponding glycol and the 1,5dichloro-tetrasilaether (ClSi2Me4)2O presented in Scheme 2.

the oxygen atom turned outward which is apparent from the large O5···Li distance of 451.8(1) pm. The Si−O−Si angle, an important parameter regarding siloxane basicity,18−23 is comparatively large. The Si2−O5−Si3 angle has a value of about 148°. Taking all observations into account, no interaction of O5 with Li+ can be observed in the solid state. The 29Si{1H} NMR experiment shows two respective singlets for the siloxane backbone with one significantly low-field shifted and one slightly high-field shifted (δ = 18.8 and 2.1 ppm) in comparison to free ligand 1. This small shift of the 29 Si{1H} signal for Si2 and Si3 (ΔδSi2/Si3 = −0.1 ppm) indicates that the conformation of the ligand is also maintained in solution with O5 showing no interactions with the Li+ ion. However, fully Si substituted oxygen atoms are still capable of coordinating Li+ ions which was shown by the partially silicon based crown ether 1,2,4,5-tetrasila[12]crown-4. In the presence of LiOTf (OTf = CF3SO3−), a remarkable downfield shift is observed from 0.9 to 9.4 ppm in deuterated dichloromethane.11 At this point, it can be summarized that the 29Si NMR experiment is a very good indicator of the strength of the interaction of a Lewis acid with the siloxane backbone as the shift is very sensitive toward coordination. A quite similar ligand behavior to that observed in 2 is also expected for the magnesium cation (ri[Mg2+]CN6 = 72 pm; CN = coordination number)24 which is in a diagonal relationship with lithium (ri[Li+]CN6 = 72 pm).24 The magnesium complex [Mg(1,2,4,5-tetrasila-benzo[15]crown-5)I2] (3) is obtained after addition of MgI2 to a solution of 1 in α,α,αtrifluorotoluene. After workup and recrystallization from dichloromethane (DCM)/n-pentane solution, colorless platelets could be obtained which were suitable for XRD. The coordination sphere of the Mg2+ cation can be interpreted as a highly distorted pentagonal bipyramid with all of the oxygen atoms as well as the two iodide anions coordinating to the metal center (see Figure 2). Whereas the fully organic and the Si/C substituted oxygen atoms share strong interactions with the Mg2+ cation, the fully Si substituted oxygen atom has much weaker interactions with the metal center. The ionic radius of Mg2+ is, at 72 pm (CN6), very close to that of Li+ at 76 pm (CN6).24 Surprisingly the siloxane backbone is still pointed to the inside of the crown ether cavity, but the O2−Mg1 distance

Scheme 2. Preparation of Ligand 1

The crown ether 1 can be obtained after workup procedures in 98% yield. The cavity size of this ligand is larger than that of [15]crown-5 but slightly smaller than that of [18]crown-6. For this reason the ligand is capable of complexing a wide range of s-block ions, e.g., Na+, Ca2+, Sr2+, but also Li+ and Mg2+ in a mismatched fashion. These (mismatched) complexes can be an indicator of whether siloxane embedded oxygen atoms interact with a Lewis acid in the solid state and whether coordination modes are maintained in solution. Treatment of 1 with LiI in α,α,α-trifluorotoluene yields the coordination compound [Li(1,2,4,5-tetrasila-benzo[15]crown-5)I] (2). Neat 2 is a slightly yellow powder which can be recrystallized after dissolution in benzene, overlayering with n-pentane and cooling the solution at −24 °C for several weeks. Colorless needles were obtained that are suitable for a single crystal Xray diffraction (XRD) experiment. The molecular structure within the crystal reveals a 5-fold-coordinated lithium ion (see Figure 1). The central ion is coordinated by two of the Si and C substituted oxygen atoms of the siloxane backbone, two oxygen atoms of the organic framework, and the iodide anion. The Li+ ion is far too small for the cavity of ligand 1 so the fully Si substituted O atom is not coordinated. The flexible siloxane backbone remains in a staggered conformation with B

DOI: 10.1021/acs.inorgchem.9b00086 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

ether cavity. The sodium ion matches well with the spanned mean plane of the five oxygen atoms as it is placed only about 43 pm above this plane. For comparison, in [Na([15]crown-5)I] the sodium ion is located 80 pm above this plane.26 Thus, the sodium ion matches better with the cavity of 1 than with that of [15]crown-5. The coordination of the three different types of O atoms is very similar to those in the complex [Li(1,2,4,5tetrasila[12]crown-4)OTf]. Whereas the Si/C substituted O atoms show the shortest distances to the metal center (237.2(2) and 243.2(2) pm), the completely silicon bonded oxygen is the longest (274.1(3) pm).11 Just like in [Li(1,2,4,5tetrasila[12]crown-4)OTf], the completely Si substituted oxygen atom in 4 has about a 30 pm greater distance to the metal center than the Si/C substituted atom and about a 20 pm greater distance than the C substituted atom. The Si2− O5−Si3 angle is decreasing to a value of 133.8(1)° with O5 pointing to Na+. This Si−O−Si angle is also very close to the Si−O−Si angle in the related lithium compound [Li(1,2,4,5-tetrasila[12]crown-4)OTf] where an angle of 134.3(1)° is found.11 The O5−Na1 distance, however, is now much closer to the residual O−Na distances indicating a stronger interaction of the siloxane backbone with the metal center than in 3. Observations made in solution confirm this argument as the NMR chemical shift of ΔδSi2/Si3 = 4.9 ppm for silicon atoms Si2 and Si3 is observed in comparison to that of free ligand 1. This shift is larger than in 3. Thus, a good match with the cavity size of the silicon based crown ether is very important along with the hardness of the cation and has to be taken into account when siloxane basicity is discussed. Overall the siloxane backbone in 4 shares moderate interactions with the Na+ metal center. As the Na+ cation matches very well with the cavity of 1, the Ca2+ cation should also be a very suitable cation for complexation. As calcium is in a diagonal relationship with sodium, the ionic radius is almost the same at 106 pm (CN7).24 Adding CaI2 to a solution of 1 in α,α,α-trifluorotoluene yields [Ca(1,2,4,5-tetrasila-benzo[15]crown-5)I2] (5). After workup procedures, single crystals for X-ray diffraction were obtained from DCM/n-pentane solution in the shape of colorless platelets. The molecular structure within the crystal reveals a pentagonal bipyramidal coordinated calcium ion in ligand 1 (see Figure 4). As can be seen here, the harder Ca2+ cation has a more significant influence toward the bonding situation of the siloxane linkage. As the OC−M as well as the OC/Si−M distances are close to those in compound 4, the OSi−M atomic distance is significantly shorter. It is now 256.0(1) pm and for this reason much closer now to the residual O−M distances. Thus, the Si−O−Si angle is also further decreased to a value of 125.9(1)° which one of the smallest angles observed so far for siloxane ligands binding to a metal center. In solution, this leads to a remarkable NMR chemical low-field shift of the silicon atoms Si2 and Si3. The respective signal is found at 14.0 ppm. This is the most low-field shifted value for all herein characterized coordination compounds (ΔδSi2/Si3 = 11.8 ppm). The slightly larger Sr2+ cation (ri[Sr2+]CN7 = 121 pm)24 can be incorporated into 1 using analogous procedures and can also be recrystallized from DCM/n-pentane solution. The coordination compound [Sr(1,2,4,5-tetrasila-benzo[15]crown-5)I2] (6) crystallizes isostructurally to 5 (see Figure 5) and for this reason also indicates a very good matching of Sr2+ with ligand 1. In comparison to 5, the crown ether is now stretched as the

Figure 2. Molecular structure of 3 in the crystal. Thermal ellipsoids represent the 50% probability level. Hydrogen atoms omitted for clarity. Only one out of four independent molecules per asymmetric unit is shown. Selected bond lengths [pm]: O1−Mg1 227.0(3), O2− Mg1 299.8(8), O3−Mg1 220.3(3), O4−Mg1 227.2(3), O5−Mg1 227.7(3), I1−Mg1 279.0(1), I2−Mg1 279.5(1). Selected bond angles [deg]: O1−Mg1−O2 77.3(1), O1−Mg1−O5 71.6(1), O2−Mg1−O3 74.2(1), O3−Mg1−O4 72.1(1), O4−Mg1−O5 65.8(1), I1−Mg1−I2 167.2(1), Si2−O2−Si3 133.9(2).

at 299.8(8) pm is significantly longer than the other O−Mg atom distances (220.3(2)−227.7(3) pm). Even though the O2−Mg1 atomic distance is very long, it is less than the sum of the van der Waals radii.25 Thus, a weak contact can be inferred. A contact is obviously enforced due to the more Lewis acidic magnesium cation. In addition, the Si2−O2−Si3 angle is, at 133.9(2)°, comparatively small. A weak interaction is further underpinned by observations made in solution since a slight NMR shift for Si2 and Si3 of ΔδSi2/Si3 = 4.6 ppm is observed between 3 and free ligand 1. A stronger interaction with the siloxane backbone is observed for the larger Na+ ion. After reaction of 1 with NaI in α,α,α-trifluorotoluene, the complex [Na(1,2,4,5-tetrasila-benzo[15]crown-5)I] (4) can be obtained as a colorless powder, Figure 3. As the compound showed no tendency to crystallize from various solvent mixtures, we were finally able to obtain just a few single crystals from melting the bulk compound and slowly cooling to ambient temperature. Colorless platelets were analyzed via XRD. The molecular structure within the crystal reveals a 6fold-coordinated sodium ion placed in the middle of the crown

Figure 3. Molecular structure of 4 in the crystal. Thermal ellipsoids represent the 50% probability level. Hydrogen atoms are omitted for clarity. Only one out of two independent molecules per asymmetric unit is shown. Selected bond lengths [pm]: O1−Na1 243.2(2), O2− Na1 252.4(3), O3−Na1 255.3(2), O4−Na1 237.2(2), O5−Na1 274.1(3), I1−Na1 304.4(1). Selected bond angles [deg]: O1−Na1− O2 66.2(1), O1−Na1−O5 80.3(1), O2−Na1−O3 56.6(1), O3− Na1−O4 66.6(1), O4−Na1−O5 82.7(1), Si2−O2−Si3 133.8(1). C

DOI: 10.1021/acs.inorgchem.9b00086 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

observed. This is due to the larger ionic radius for Sr2+. Hence, the OSi−M atomic distance is, with 260.8(2) pm, again very close to those of the OC/Si−M (252.3(2) and 252.4(2) pm) but especially the OC−M (258.9(2) and 257.1(2) pm) distances. Similar to that of 5, the NMR chemical shift of 6 is distinct. The respective signal of Si2 and Si3 is found at 13.7 ppm (ΔδSi2/Si3 = 11.5 ppm). On a structural level, Sr2+ rather than Ca2+ seems to be the most suitable cation for ligand 1 as the OSi−M distance is in better harmony with the OC−M distances. As observed in solution, however, the Ca2+ cation shares stronger interactions which follow the general trend that hard cations share stronger interactions with the siloxane backbone than soft ions do.13 In this work, experimental details hint that harder cations share stronger interactions not only with oxygen atoms bonded to silicon as well as carbon but also with oxygen atoms bonded exclusively to silicon, as long as the cation is not far too small for the cyclic ligand as for example in complex 2. Taking all these observations into account one can conclude that a perfect match of a hard cation with the crown ether cavity can make siloxane oxygen atoms available for effective coordination. As the coordination chemistry of hard group 1 and 2 metal ions turned out to be successful, the 29Si NMR chemical shifts are summarized in Figure 6. As can be seen here, the shifts are highly sensitive toward coordination, and the choice of the Lewis acid and ligand can reveal very different coordination modes which are very well-represented in solution. No interactions of the Si−O−Si moiety of ligand 1 with M could be observed with M = Li+; weak interactions with M = Mg2+, moderate interactions with M = Na+, and strong interactions with M = Ca2+ and Sr2+ could be observed. This class of ligand opens up for further investigations hard group 2 cations such as Be2+, which are currently underway.27,28 For barium, the heaviest nonradioactive alkaline earth metal, we decided to choose 1,2,4,5-tetrasila[18]crown-6 (7) as a ligand for complexation. As the ionic radius of Ba 2+ (ri[Ba2+]CN9 = 147 pm)24 is even larger, the cavity of 1 is too small for 1:1 complex formation. As is evident from the disila-crown ether analogue of [15]crown-5, it could be shown that this crown ether yields a dinuclear species [Ba2(1,2disila[15]crown-5)OTf4].9 Thus, 7, which is accessible by

Figure 4. Molecular structure of 5 in the crystal. Thermal ellipsoids represent the 50% probability level. Hydrogen atoms are omitted for clarity. Selected bond lengths [pm]: O1−Ca1 242.9(1), O2−Ca1 249.8(1), O3−Ca1 247.8(1), O4−Ca1 241.8(1), O5−Ca1 256.0(1), I1−Ca1 305.4(1), I2−Ca1 307.4(1). Selected bond angles [deg]: O1−Ca1−O2 66.5(1), O1−Ca1−O5 83.0(1), O2−Ca1−O3 61.9(1), O3−Ca1−O4 66.7(1), O4−Ca1−O5 82.4(1), I1−Ca1−I2 176.8(1), Si2−O2−Si3 125.9(1).

Figure 5. Molecular structure of 6 in the crystal. Thermal ellipsoids represent the 50% probability level. Hydrogen atoms are omitted for clarity. Selected bond lengths [pm]: O1−Sr1 252.4(2), O2−Sr1 258.9(2), O3−Sr1 257.1(2), O4−Sr1 252.3(2), O5−Sr1 260.8(2), I1−Sr1 317.9(1), I2−Sr1 320.5(1). Selected bond angles [deg]: O1− Sr1−O2 65.2(1), O1−Sr1−O5 84.7(1), O2−Sr1−O3 60.7(1), O3− Sr1−O4 65.5(1), O4−Sr1−O5 84.0(1), I1−Sr1−I2 175.6(1), Si2− O2−Si3 129.9(1).

Si−O−Si angle is increased to a value of 129.9(1)°. Despite the larger Si−O−Si angle, a strong Sr−O5 interaction is

Figure 6. 29Si NMR chemical shifts of alkali and alkaline earth metal complexes of the partially silicon based crown ether 1,2,4,5-tetrasilabenzo[15]crown-5 (1) in deuterated dichloromethane at 300 K. D

DOI: 10.1021/acs.inorgchem.9b00086 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry reaction of tetraethylene glycol with O(Si2Me4Cl)2,9 was the ligand of choice. Reaction of 7 with BaI2 yields a slight yellow powder which can be recrystallized from DCM/n-pentane solution. Crystals suitable for XRD were obtained in the shape of colorless needles. Unusually, the molecular structure in the crystal reveals the dinuclear species [Ba2(1,2,4,5-tetrasila[18]crown-6)2I4] (8) (Figure 7). In contrast to this molecular structure, [Ba(1,2-disila[18]crown-6)OTf2] and [Ba(1,2-disilabenzo[18]crown-6)OTf2] are monomeric contact ion pairs.10

the coordination chemistry to other partially silicon based crown ethers bearing a O−Si2Me4−O−Si2Me4−O moiety. In this work we synthesized the partially silicon based crown ether 1,2,4,5-tetrasila-benzo[15]crown-5 (1). The ligand turned out to be suitable for complexation of a wide range of s-block ions. Furthermore, salts of the strongly coordinating anion I− were suitable, showing a fair complexation ability of this ligand. By equimolar reaction of 1 with alkali or alkaline earth metal iodides, we obtained the alkali metal complexes 2 and 4 and the alkaline earth metal complexes 3, 5, and 6. Depending on the ionic radii, different coordination modes were established which could be well-represented by observations made in solution. The 29Si NMR experiment turned out to be a very good indicator for the strength of interaction between a Lewis acid and the siloxane backbone as the chemical shift is very sensitive toward coordination. Whereas the Li+ cation shows no interaction with the siloxane oxygen atom, the harder magnesium cation enforces coordination. Both experiments, XRD and NMR, are consistent. However, both cations were too small for the cavity of 1. The larger Na+ ion fits well, and thus, the NMR chemical shift is more distinct although the Na+ ion is less hard than the Mg2+ cation. Ca2+ and Sr2+, both cations which match well with the cavity of 1, exhibit a hard character and for this reason share very strong interactions with the siloxane backbone. The molecular structures of compounds 5 and 6 show comparatively small Si−O−Si angles, and the NMR chemical shift is significantly more low-field shifted in comparison to all other characterized compounds. It might be concluded that there is a special ion selectivity of partially silicon based crown ethers. This will be the subject of future research. Those cations which exhibit a hard character and fit perfectly with the cavity of the ligand can activate Si embedded oxygen atoms for effective coordination. In this study, the OSi− M distance is in best harmony with the OC−M distances in compound 6 on a structural level and compound 5 regarding NMR chemical shift as the attraction of OSi with M being the strongest observed here. However, if given a choice where to place the ion in the cavity, the OSi−M distance is the largest in all compounds. The results are summarized in Scheme 3. A siloxane coordination with barium as the central ion could be established by reaction of 7 with BaI2. The dinuclear complex [Ba2(1,2,4,5-tetrasila[18]crown-6)2I4] (8) could be characterized, and the argument that a harder cation interacts with silicon based ligands stronger than soft cations do could be further strengthened. Overall, the successful incorporation of a wide range of s-block metal ions is promising for future coordination chemistry of siloxane compounds. Further, the coordination chemistry of siloxane embedded oxygen atoms toward Lewis acids has been advanced and challenges the widespread opinion of (cyclo)siloxanes as weakly coordinating ligands.

Figure 7. Molecular structure of 7 in the crystal. Thermal ellipsoids represent the 40% probability level. Hydrogen atoms are omitted for clarity. All nonlabeled atoms are symmetry generated over 1 − x, 1 − x, 2 − z. Selected bond lengths [pm]: O1−Ba1 286.7(5), O2−Ba1 278.8(6), O3−Ba1 291.3(1), O4−Ba1 284.6(5), O5−Ba1 283.4(5), O6−Ba1 338.8(1), I1−Ba1 352.0(1), I2−Ba1 342.3(1), Ba1···Ba1# 560.1(1). Selected bond angles [deg]: O1−Ba1−O2 55.9(1), O1− Ba1−O6 65.6(1), O2−Ba1−O3 56.6(1), O3−Ba1−O4 57.4(1), O4− Ba1−O5 59.7(1), O5−Ba1−O6 71.1(1), I1−Ba1−I2 139.4(1), Ba1− I1−Ba1# 105.1(1), Si2−O2−Si3 133.5(4).

The central barium cations are coordinated by all of the crown ether oxygen atoms, but similar to compound 3 the OSi−M distance is at 338.8(1) pm by far the longest. Beside the crown ethers, three iodide anions coordinate to each metal ion. Two iodide anions act as bridges between the Ba2+ ions and saturate the coordination sphere. Barium is overall 9-foldcoordinated in a highly distorted crown ether environment. We discussed the enlarged cavity size of 7 in a previous work as we targeted synthesis of the corresponding alkali metal complex [K(1,2,4,5-tetrasila[18]crown-6)PF6].9 The potassium ion is with 151 pm (CN8)24 slightly larger than the Ba2+ cation, but the coordination mode is significantly different. As shown via XRD and 29Si NMR chemical shift, the siloxane backbone shares no interaction with the potassium cation. Barium, however, does share moderate interactions with it. Even though the OSi−M distance is very long, the NMR experiment proves the interaction of O6 with Ba2+ as can be seen by a shift of ΔδSi2/Si3 = 8.3 ppm in comparison to free ligand 7.

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EXPERIMENTAL SECTION

General. All manipulations were carried out with rigorous exclusion of oxygen and moisture using basic Schlenk techniques establishing an inert-gas atmosphere. Solvents were dried and freshly distilled before use. Compound 7 and the organic fragment of 1 were synthesized using methods described in the literature.9,29 Alkali and alkaline earth metal salts were dried in vacuo and handled under an argon atmosphere using a glovebox of MBraun-type. NMR spectra were recorded on different Bruker spectrometers including an AV III HD 300 MHz or an AV III 500 MHz. Infrared (IR) spectra of the respective samples were measured using the attenuated total

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CONCLUSION In a recent work, we described the synthesis of the hybrid tetrasila-crown ether 1,2,4,5-tetrasila[12]crown-4. This crown ether and its respective lithium complex have been the only examples where a O−Si2Me4−O−Si2Me4−O unit coordinate a metal cation.11 This promising result motivated us to extend E

DOI: 10.1021/acs.inorgchem.9b00086 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

temperature and is then stirred overnight. The solvent is removed under reduced pressure and the remaining solid dissolved in 5 mL DCM. After centrifugation and decantation, the solvent is yet again removed under reduced pressure to obtain a slight yellow, greasy solid. After washing with 3 mL of n-pentane, 2 is obtained as a slight yellow wax-like powder (0.151 g, 97%). For single crystal growth, the powder is dissolved in 3 mL of benzene and layered with 20 mL of npentane. Storage at −24 °C yields a few single crystals in the shape of colorless needles within a few weeks. 1 H NMR (300 MHz, CD2Cl2): δ = 0.27 (s, 12H, Si(CH3)2), 0.34 (s, 12H, Si(CH3)2), 4.25 (s, 8H, CH2), 6.98−7.07 (m, 4H, CHAr) ppm. 7Li NMR (117 MHz, CD2Cl2): δ = 0.33 (s, LiI). 13C{1H} NMR (125 MHz, CD2Cl2): δ = −0.5 (s, Si(CH3)2), 2.7 (s, Si(CH3)2), 62.1 (s, CH2), 71.1 (s, CH2), 114.4 (s, CHAr), 123.5 (s, CHAr), 147.5 (s, CHAr, q) ppm. 29Si{1H} NMR (60 MHz, CD2Cl2): δ = 18.8 (s, SiCH3), 2.1 (s, SiCH3) ppm. ESI(+) m/z (%): 451.1807 [M − I]+ (100). IR (cm−1): 2961 (m), 2886 (w), 1597 (w), 1502 (m), 1457 (w), 1400 (w), 1372 (w), 1324 (w), 1257 (s), 1207 (w), 1018 (vs), 933 (s), 858 (m), 796 (vs), 765 (vs), 685 (s), 661 (m), 641 (m), 606 (w), 554 (w), 453 (w). [Mg(1,2,4,5-tetrasila-benzo[15]crown-5)I2] (3). A 0.140 g portion of 1,2,4,5-tetrasila-benzo[15]crown-5 (0.32 mmol) is dissolved in 10 mL of α,α,α-trifluorotoluene. Subsequently, 0.088 g (0.32 mmol) of MgI2 is added. The resulting suspension is stirred vigorously overnight. The solvent is removed under reduced pressure, and the remaining solid is dissolved in 10 mL DCM. After centrifugation and decantation, the solvent is yet again removed under reduced pressure to obtain a slight yellow powder. Washing the powder with 4 mL of npentane yields 3 as a colorless powder (0.200 g, 88%). For single crystal growth, the powder is dissolved in 4 mL of DCM and layered with 25 mL of n-pentane. Single crystals in the shape of colorless platelets are obtained after 3 days. 1 H NMR (300 MHz, CD2Cl2): δ = 0.46 (s, 12H, Si(CH3)2), 0.48 (s, 12H, Si(CH3)2), 4.29−4.31 (m, 4H, CH2), 4.39−4.41 (m, 4H, CH2), 6.93−6.96 (m, 2H, CHAr), 7.07−7.11 (m, 2H, CHAr) ppm. 13 C{1H} NMR (125 MHz, CD2Cl2): δ = 0.0 (s, Si(CH3)2), 3.86 (s, Si(CH3)2), 60.9 (s, CH2), 67.7 (s, CH2), 111.6 (s, CHAr), 123.3 (s, CHAr), 144.7 (s, CHAr,q) ppm. 29Si{1H} NMR (60 MHz, CD2Cl2): δ = 21.0 (s, SiCH3), 6.8 (s, SiCH3) ppm. MS ESI(+) m/z (%): 595.0546 [M − I]+ (100), 911.3201 [2M − MgI2 + Na]+ (5), 1039.2207 [2M − I]+ (20). IR (cm−1): 2960 (w), 2891 (vw), 1598 (vw), 1504 (m), 1457 (w), 1401 (vw), 1333 (vw), 1252 (s), 1200 (m), 1125 (m), 1032 (s), 936 (s), 857 (m), 800 (vs), 767 (vs), 746 (vs), 714 (s), 649 (m), 607 (m), 540 (w), 455 (vw). CHN Calcd for C18H36I2MgO5Si4·0.5DCM: C, 29.03; H, 4.87. Found: C, 28.93; H, 4.84. [Na(1,2,4,5-tetrasila-benzo[15]crown-5)I] (4). A 0.350 g portion of 1,2,4,5-tetrasila-benzo[15]crown-5 (0.79 mmol) is dissolved in 10 mL of α,α,α-trifluorotoluene. Subsequently, 0.118 g (0.79 mmol) of NaI is added. The resulting suspension is stirred vigorously and is heated to reflux several times. The suspension is allowed to cool to ambient temperature and is then stirred overnight. The solvent is removed under reduced pressure and the remaining solid dissolved in 10 mL of DCM. After centrifugation and decantation, the solvent is yet again removed under reduced pressure to obtain a greasy solid. After washing several times with 3 mL portions of n-pentane, 4 is obtained as a slight yellow wax-like powder (0.250 g, 53%). For single crystal growth the compound is gently melted several times using a heat gun. A few very small single crystals in the shape of colorless platelets are then obtained by allowing the melt to slowly cool to ambient temperature. 1 H NMR (300 MHz, CD2Cl2): δ = 0.35 (s, 12H, Si(CH3)2), 0.35 (s, 12H, Si(CH3)2), 4.08−4.12 (m, 4H, CH2), 4.16−4.20 (m, 4H, CH2), 6.86−6.98 (m, 4H, CHAr) ppm. 13C{1H} NMR (125 MHz, CD2Cl2): δ = −0.6 (s, Si(CH3)2), 3.1 (s, Si(CH3)2), 61.5 (s, CH2), 69.3 (s, CH2), 112.0 (s, CHAr), 122.0 (s, CHAr), 147.5 (s, CHAr, q) ppm. 29Si{1H} NMR (60 MHz, CD2Cl2): δ = 15.1 (s, SiCH3), 7.1 (s, SiCH3) ppm. MS ESI(+) m/z (%): 467.1545 [M − I]+ (100). IR (cm−1): 2949 (m), 2876 (w), 1596 (w), 1504 (s), 1456 (m), 1402 (w), 1372 (w), 1333 (w), 1248 (s), 1216 (s), 1125 (s), 1081 (s),

Scheme 3. Coordination Chemistry of the Partially Silicon Based Crown Ethers 1,2,4,5-tetrasila[15]crown-5 (1) and 1,2,4,5-tetrasila[18]crown-6 (7)

reflectance (ATR) mode on the Bruker-type spectrometer Alpha FTIR. ESI mass spectra were acquired with an LTQ-FT Ultra mass spectrometer (Thermo Fischer Scientific). The resolution was set to 100.000. Elemental analysis was carried out on a Vario MicroCube. In the case of the alkali metal compounds 2 and 4, we have not been able to obtain an accurate CH-analysis. This is probably due to the waxlike, greasy characteristics of the compounds and/or formation of SiC. Synthesis and Crystallization. 1,2,4,5-Tetrasila-benzo[15]crown-5 (1). A 0.676 g portion of 2,2′-[1,2-phenylenebis(oxy)]diethanol (3.41 mmol, 1.0 equiv) and 0.89 mL of NEt3 (6.42 mmol, 2.0 equiv) are dissolved in 25 mL of THF (THF = tetrahydrofuran). Subsequently, 1 mL of O(Si2Me4Cl)2 (3.41 mmol, 1.0 equiv) dissolved in 25 mL of THF is added over a period of 60 min. The resulting white suspension is then stirred overnight and is freed of the solvent. The residue is extracted with 50 mL of n-pentane followed by filtration. Removing the solvent under reduced pressure yields crown ether 1 as a colorless oil (1.500 g, 98%). 1 H NMR (300 MHz, C6D6): δ = 0.31 (s, 12H, Si(CH3)2), 0.32 (s, 12H, Si(CH3)2), 3.81−3.90 (m, 8H, CH2), 6.69−6.83 (m, 4H, CHAr) ppm. 13C{1H} NMR (125 MHz, C6D6): δ = −0.3 (s, Si(CH3)2), 2.8 (s, Si(CH3)2), 63.0 (s, CH2), 71.1 (s, CH2), 115.0 (s, CHAr), 121.6 (s, CHAr), 150.1 (s, CHAr,q) ppm. 29Si{1H} NMR (60 MHz, C6D6): δ = 12.7 (s, SiCH3), 3.8 (s, SiCH3) ppm. 29Si{1H} NMR (60 MHz, CD2Cl2): 11.8 (s, SiCH3), 2.2 (s, SiCH3). ESI(+) m/z (%): 445.1730 [M + H]+ (5), 467.1553 [M + Na]+ (100). IR (cm−1): 2949 (m), 2871 (w), 1593 (w), 1501 (m), 1452 (w), 1399 (w), 1372 (w), 1328 (w), 1246 (s), 1221 (m), 1124.58 (s), 1098 (s), 1033 (vs), 953 (m), 924 (m), 824 (m), 797 (s), 761 (vs), 738 (vs), 681 (m), 660 (m), 635 (m), 552 (w), 485 (w), 461 (w). [Li(1,2,4,5-tetrasila-benzo[15]crown-5)I] (2). A 0.120 g portion of 1,2,4,5-tetrasila-benzo[15]crown-5 (0.27 mmol) is dissolved in 10 mL of α,α,α-trifluorotoluene. Subsequently, 0.036 g (0.27 mmol) of LiI is added. The resulting suspension is stirred vigorously and is heated to reflux several times. The suspension is allowed to cool to ambient F

DOI: 10.1021/acs.inorgchem.9b00086 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

CH2), 70.9 (s, CH2), 73.3 (s, CH2) ppm. 29Si{1H} NMR (60 MHz, CD2Cl2): δ = 18.3 (s, SiCH3), 10.2 (s, SiCH3) ppm. MS ESI(+) m/z (%): 509.1440 [M − BaI2 − 2I]2+ (30), 705.0019 [0.5M − I]+ (30). IR (cm−1): 2962 (m), 2908 (w), 2879 (w), 1466 (w), 1401 (w), 1347 (w), 1258 (s), 1085 (s), 1064 (s), 1019 (s), 950 (m), 928 (m), 855 (m), 797 (vs), 763 (vs), 720 (m), 696 (m), 634 (m), 519 (w), 448 (w). CHN Calcd for C32H80I4Ba2O12Si8·0.5DCM: C, 22.66; H, 4.73. Found: C, 22.49; H, 4.70. Crystal Structures. Single crystal X-ray diffraction experiments were performed on a Bruker D8 Quest (4), STOE IPDS2 (3, 5, 6), STOE IPDS2T (2), or a STOE STADIVARI (8) diffractometer, respectively. Measurements were performed at 100 K with Mo Kα (λ = 0.71073 Å) or Cu Kα (λ = 1.54184 Å) radiation, graphite monochromatization, and/or respective X-ray optics. The structures were solved by direct methods and refinement with full-matrix-leastsquares against F2 using SHELXT and SHELXL on the OLEX2 platform.30−32 The crystallographic data for all compounds are deposited in the Cambridge Crystallographic Data Centre (CCDC). The deposition numbers are 1871016 (2), 1871015 (3), 1871018 (4), 1871019 (5), 1871014 (6), and 1871017 (8). Crystal Data for 2·0.5C6H6. C21H39ILiO5Si4, triclinic, P1̅, Z = 8, 100(2) K, a = 10.2359(9) Å, b = 23.042(2) Å, c = 26.871(3) Å, α = 93.509(8)°, β = 90.275(7)°, γ = 92.139(7)°, V = 6321.1(10) Å3, ρ = 1.298 g cm−3, spherical absorption correction using STOE X-AREA and LANA,32 μ = 1.190 mm−1, Tmin, Tmax = 0.2116, 0.9235, 2Θ range 3.422−50.00°, reflections measured 49 969, independent reflections 22 236 [R(int) = 0.1054], 1185 parameters, R-index [I ≥ 2σ(I)] 0.0677, wR2 (all data) 0.1776, GOF 0.921, Δρmax, Δρmin 1.15/−1.31 e Å3. Crystal Data for 3. C18H36I2MgO5Si4, triclinic, P1̅, Z = 8, 100(2) K, a = 17.9132(11) Å, b = 18.8637(12) Å, c = 19.2796(11) Å, α = 94.842(5)°, β = 100.546(5)°, γ = 93.294(5)°, V = 6364.2(7) Å3, ρ = 1.509 g cm−3, spherical absorption correction using STOE X-AREA and LANA,33 μ = 2.169 mm−1, Tmin, Tmax = 0.2908, 0.6373, 2Θ range 2.854−56.998°, reflections measured 81 360, independent reflections 32 228 [R(int) = 0.0361], 1113 parameters, R-index [I ≥ 2σ(I)] 0.0455, wR2 (all data) 0.1244, GOF 1.019, Δρmax, Δρmin 3.76/−1.43 e Å3. Crystal Data for 4. C18H36INaO5Si4, monoclinic, P21/n, Z = 8, 100(2) K, a = 13.1247(6) Å, b = 21.0454(10) Å, c = 20.7966(9) Å, β = 97.757(2)°, V = 5691.8(4) Å3, ρ = 1.388 g cm−3, multiscan absorption correction using SADABS2016,34 μ = 1.332 mm−1, Tmin, Tmax = 0.6940, 0.7452, 2Θ range 4.346−50.816°, reflections measured 121 055, independent reflections 10 476 [R(int) = 0.1016], 539 parameters, R-index [I ≥ 2σ(I)] 0.0425, wR2 (all data) 0.0750, GOF 1.070, Δρmax, Δρmin 0.83/−0.63 e Å3. Crystal Data for 5. C18H36CaI2O5Si4, monoclinic, P21/c, Z = 4, 100(2) K, a = 18.5850(16) Å, b = 9.7165(6) Å, c = 18.0271(14) Å, β = 110.406(6)°, V = 3051.1(4) Å3, ρ = 1.608 g cm−3, spherical absorption correction using X-AREA and LANA,33 μ = 2.410 mm−1, Tmin, Tmax = 0.1713, 0.4121, 2Θ range 4.566−58.00°, reflections measured 26 254, independent reflections 8101 [R(int) = 0.0281], 279 parameters, R-index [I ≥ 2σ(I)] 0.0298, wR2 (all data) 0.0763, GOF 0.989, Δρmax, Δρmin 1.39/−0.49 e Å3. Crystal Data for 6. C18H36SrI2O5Si4, monoclinic, P21/c, Z = 4, 100(2) K, a = 18.737(10) Å, b = 9.797(6) Å, c = 18.118(10) Å, β = 110.85(4), V = 3108(3) Å3, ρ = 1.680 g cm−3, spherical absorption correction using X-AREA and LANA,33 μ = 3.898 mm−1, Tmin, Tmax = 0.1185, 0.1765, 2Θ range 4.538−57.00°, reflections measured 20 092, independent reflections 7840 [R(int) = 0.0281], 279 parameters, Rindex [I ≥ 2σ(I)] 0.0261, wR2 (all data) 0.0567, GOF 0.925, Δρmax, Δρmin 0.94/−0.33 e Å3. Crystal Data for 8. C32H80Ba2I4O12Si8, monoclinic, P21/n, Z = 2, 100(2) K, a = 10.7039(7) Å, b = 18.8316(13) Å, c = 16.4914(12) Å, β = 103.155(5), V = 3237.0(4) Å3, ρ = 1.707 g cm−3, spherical absorption correction using X-AREA and LANA,33 μ = 26.144 mm−1, Tmin, Tmax = 0.0201, 0.0009, 2Θ range 7.234−136.00°, reflections measured 28 610, independent reflections 5885 [R(int) = 0.0518], 270 parameters, R-index [I ≥ 2σ(I)] 0.0573, wR2 (all data) 0.1685, GOF 1.058, Δρmax, Δρmin 2.60/−1.56 e Å3.

1044 (s), 952 (vs), 931 (s), 854 (m), 827 (m), 805 (s), 765 (vs), 727 (s), 694 (s), 638 (m), 602 (w), 533 (w), 457 (w). [Ca(1,2,4,5-tetrasila-benzo[15]crown-5)I2] (5). A 0.222 g portion of 1,2,4,5-tetrasila-benzo[15]crown-5 (0.50 mmol) is dissolved in 10 mL of α,α,α-trifluorotoluene. Subsequently, 0.147 g (0.50 mmol) of CaI2 is added. The resulting suspension is stirred vigorously overnight. The solvent is removed under reduced pressure and the remaining solid dissolved in 10 mL of DCM. After centrifugation and decantation, the solvent is yet again removed under reduced pressure. The residue is washed with 4 mL of n-pentane, and 5 is then obtained as a pale white powder (0.330 g, 89%). For single crystal growth, the powder is dissolved in 4 mL of DCM and layered with 20 mL of npentane. Single crystals in the shape of colorless platelets are obtained overnight. 1 H NMR (300 MHz, CD2Cl2): δ = 0.51 (s, 12H, Si(CH3)2), 0.60 (s, 12H, Si(CH3)2), 4.34−4.41 (m, 8H, CH2), 6.94−6.98 (m, 2H, CHAr), 7.04−7.09 (m, 2H, CHAr) ppm. 13C{1H} NMR (125 MHz, CD2Cl2): δ = −0.45 (s, Si(CH3)2), 4.13 (s, Si(CH3)2), 62.4 (s, CH2), 69.0 (s, CH2), (s, CH2), 111.6 (s, CHAr), 123.2 (s, CHAr), 146.0 (s, CHAr, q) ppm. 29Si{1H} NMR (60 MHz, CD2Cl2): δ = 21.2 (s, SiCH3), 14.0 (s, SiCH3) ppm. MS ESI(+) m/z (%): 467.1544 [M − CaI2 + Na]+ (50), 611.0321 [M − I]+ (40), [2M − CaI2 − I]+ (10). IR (cm−1): 2943 (w), 2882 (w), 1505 (w), 1459 (w), 1394 (w), 1350 (w), 1255 (s), 1126 (w), 1076 (s), 1042 (s), 974 (m), 948 (s), 931 (s), 855 (m), 798 (vs), 772 (vs), 735 (s), 721 (s), 634 (w), 515 (w), 458 (w), 426 (w). CHN Calcd for C18H36I2CaO5Si4: C, 29.27; H, 4.91. Found: C, 29.19; H, 4.82. Synthesis of [Sr(1,2,4,5-tetrasila-benzo[15]crown-5)I2] (6). A 0.222 g portion of 1,2,4,5-tetrasila-benzo[15]crown-5 (0.50 mmol) is dissolved in 10 mL of α,α,α-trifluorotoluene. Subsequently, 0.170 g (0.50 mmol) of SrI2 is added. The resulting suspension is stirred vigorously overnight. The solvent is removed under reduced pressure and the remaining solid dissolved in 10 mL of DCM. After centrifugation and decantation the solvent is yet again removed under reduced pressure to obtain a white powder. The residue is washed with 4 mL of n-pentane, and 6 is then obtained as a pale white powder (0.351 g, 89%). For single crystal growth, the powder is dissolved in 4 mL of DCM and layered with 20 mL of n-pentane. Single crystals in the shape of colorless platelets are obtained overnight. 1 H NMR (300 MHz, CD2Cl2): δ = 0.56 (s, 12H, Si(CH3)2), 0.63 (s, 12H, Si(CH3)2), 4.38−4.49 (m, 4H, CH2), 4.45−4.47 (m, 4H, CH2), 7.03−7.06 (m, 2H, CHAr), 7.11−7.13 (m, 2H, CHAr) ppm. 13 C{1H} NMR (125 MHz, CD2Cl2): δ = −0.80 (s, Si(CH3)2), 3.42 (s, Si(CH3)2), 62.2 (s, CH2), 69.3 (s, CH2), (s, CH2), 111.8 (s, CHAr), 122.9 (s, CHAr), 145.6 (s, CHAr, q) ppm. 29Si{1H} NMR (60 MHz, CD2Cl2): δ = 20.1 (s, SiCH3), 13.7 (s, SiCH3) ppm. MS ESI(+) m/z (%): 467.1544 [M − SrI2 + Na]+ (10), 658.9751 [M − I]+ (100), 1444.8566 [2M − I]+ (15). IR (cm−1): 2942 (w), 2879 (w), 1596 (vw), 1502 (m), 1453 (w), 1249 (w), 1190 (w), 1122 (m), 1074 (s), 1035 (s), 947 (s), 922 (m), 898 (m), 846 (m), 798 (vs), 772 (vs), 718 (s), 691 (m), 638 (w), 603 (vw), 573 (vw), 530 (vw), 451 (w). CHN Calcd for C18H36I2SrO5Si4: C, 27.50; H, 4.62. Found: C, 28.13; H, 4.54. Synthesis of [Ba2(1,2,4,5-tetrasila[18]crown-6)2I4] (8). A 0.100 g portion 1,2,4,5-tetrasila[18]crown-6 (0.23 mmol) is dissolved in 10 mL of α,α,α-trifluorotoluene. Subsequently, 0.090 g (0.23 mmol) of BaI2 is added. The resulting suspension is heated to reflux several times and stirred vigorously for 1 week. The solvent is removed under reduced pressure and the remaining solid dissolved in 8 mL of DCM. After centrifugation and decantation, the solvent is yet again removed under reduced pressure. Washing the residue with two 4 mL portions of n-pentane yields 8 as a yellow powder (0.180 g, 95%). For single crystal growth, the powder is dissolved in 4 mL of DCM and layered with 20 mL of n-pentane. Single crystals in the shape of colorless needles are obtained within 2 days. 1 H NMR (300 MHz, CD2Cl2): δ = 0.42 (s, 12H, Si(CH3)2), 0.49 (s, 12H, Si(CH3)2), 3.82−3.84 (m, 4H, CH2), 3.94 (s, 8H, CH2), 4.08−4.09 (m, 4H, CH2), ppm. 13C{1H} NMR (125 MHz, CD2Cl2): δ = −0.30 (s, Si(CH3)2), 4.03 (s, Si(CH3)2), 63.6 (s, CH2), 70.7 (s, G

DOI: 10.1021/acs.inorgchem.9b00086 Inorg. Chem. XXXX, XXX, XXX−XXX

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(11) Reuter, K.; Thiele, G.; Hafner, T.; Uhlig, F.; von Hänisch, C. Synthesis and coordination ability of a partially silicon based crown ether. Chem. Commun. 2016, 52, 13265−13268. (12) Dankert, F.; Reuter, K.; Donsbach, C.; von Hänisch, C. Hybrid Disila-Crown Ethers as Hosts for Ammonium Cations: The O−Si− Si−O Linkage as an Acceptor for Hydrogen Bonding. Inorganics 2018, 6, 15. (13) Dankert, F.; Donsbach, C.; Mais, C.-N.; Reuter, K.; von Hänisch, C. Alkali and Alkaline Earth Metal Derivatives of DisilaBridged Podands: Coordination Chemistry and Structural Diversity. Inorg. Chem. 2018, 57, 351−359. (14) Martín-Fernández, C.; Montero-Campillo, M. M.; Alkorta, I.; Elguero, J. Weak interactions and cooperativity effects on disiloxane: a look at the building block of silicones. Mol. Phys. 2018, 116, 1539− 1550. (15) Harder, S.; Freitag, B.; Stegner, P.; Pahl, J.; Naglav, D. Strontium Chemistry with Silicone Grease. Z. Anorg. Allg. Chem. 2015, 641, 2129−2134. (16) Freitag, B.; Stegner, P.; Thum, K.; Fischer, C. A.; Harder, S. Tetranuclear Strontium and Barium Siloxide/Amide Clusters in Metal-Ligand Cooperative Catalysis. Eur. J. Inorg. Chem. 2018, 2018, 1938−1944. (17) Pahl, J.; Elsen, H.; Friedrich, A.; Harder, S. Unsupported metal silyl ether coordination. Chem. Commun. 2018, 54, 7846−7849. (18) Cypryk, M.; Apeloig, Y. Ab Initio Study of Silyloxonium Ions. Organometallics 1997, 16, 5938−49. (19) West, R.; Wilson, L. S.; Powell, D. L. Basicity of siloxanes, alkoxysilanes and ethers toward hydrogen bonding. J. Organomet. Chem. 1979, 178, 5−9. (20) Grabowsky, S.; Hesse, M. F.; Paulmann, C.; Luger, P.; Beckmann, J. How to Make the Ionic Si-O Bond More Covalent and the Si-O-Si Linkage a Better Acceptor for Hydrogen Bonding. Inorg. Chem. 2009, 48, 4384−4393. (21) Grabowsky, S.; Beckmann, J.; Luger, P. The Nature of Hydrogen Bonding Involving the Siloxane Group. Aust. J. Chem. 2012, 65, 785. (22) Frolov, Y. L.; Voronkov, M. G.; Strashnikova, N. V.; Shergina, N. I. Hydrogen bonding involving the siloxane group. J. Mol. Struct. 1992, 270, 205−215. (23) Fugel, M.; Hesse, M. F.; Pal, R.; Beckmann, J.; Jayatilaka, D.; Turner, M. J.; Karton, A.; Bultinck, P.; Chandler, G. S.; Grabowsky, S. Covalency and Ionicity Do Not Oppose Each Other-Relationship Between Si−O Bond Character and Basicity of Siloxanes. Chem. - Eur. J. 2018, 24, 15275−15286. (24) Shannon, R. Revised Effective Ionic Radii and Systematic Studies of Interatomic distances in Halides and Chalcogenides. Acta Crystallogr., Sect. A: Cryst. Phys., Diffr., Theor. Gen. Crystallogr. 1976, A32, 751−767. (25) Mantina, M.; Chamberlin, A. C.; Valero, R.; Cramer, C. J.; Truhlar, D. G. Consistent van der Waals Radii for the Whole Main Group. J. Phys. Chem. A 2009, 113, 5806−5812. (26) Buchanan, G. W.; Gerzain, M.; Bensimon, C. 1,4,7,10,13Pentaoxacyclopentadecane (15-crown-5) sodium iodide complex, C10H20O5NaI. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 1994, 50, 1016−1019. (27) Buchner, M. R.; Müller, M.; Dankert, F.; Reuter, K.; von Hänisch, C. The coordination behaviour and reactivity of partially silicon based crown ethers towards beryllium chloride. Dalton Trans. 2018, 47, 16393−16397. (28) Naglav, D.; Buchner, M. R.; Bendt, G.; Kraus, F.; Schulz, S. Off the Beaten Track-A Hitchhiker’s Guide to Beryllium Chemistry. Angew. Chem., Int. Ed. 2016, 55, 10562−10576. Naglav, D.; Buchner, M. R.; Bendt, G.; Kraus, F.; Schulz, S. Angew. Chem. 2016, 128, 10718−10733. (29) Peshkova, M. A.; Timofeeva, N. V.; Grekovich, A. L.; Korneev, S. M.; Mikhelson, K. N. Novel Ionophores for Barium-Selective Electrodes: Synthesis and Analytical Characterization. Electroanalysis 2010, 22, 2147−2156.

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Accession Codes

CCDC 1871014−1871019 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by the Deutsche Forschungsgemeinschaft (DFG). Dr. C. Donsbach and C. Ritter are gratefully acknowledged for their valuable help with X-ray crystallographic data. Further, F.D. thanks the MS (Dr. U. Linne and co-workers−especially J. Bamberger) and X-ray Departments (M. Marsch, R. Riedel, and Dr. K. Harms), Philipps-Universität, Marburg, for measurement time. In particular, R. Riedel is gratefully acknowledged for data collection of compounds 4 and 8.

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REFERENCES

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DOI: 10.1021/acs.inorgchem.9b00086 Inorg. Chem. XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.inorgchem.9b00086 Inorg. Chem. XXXX, XXX, XXX−XXX