A Neutral Polynuclear Chain Compound - ACS Publications

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Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

[PtZn2Ge18(Hyp)8] (Hyp = Si(SiMe3)3): A Neutral Polynuclear Chain Compound with Ge9(Hyp)3 Units Oleksandr Kysliak,† Dung D. Nguyen,‡ Andre Z. Clayborne,*,§ and Andreas Schnepf*,† †

Institute of Inorganic Chemistry, University Tübingen, Auf der Morgenstelle 18, D-72076 Tübingen, Germany Department of Chemistry, University of MissouriKansas City, 5110 Rockhill Road, Kansas City, Missouri 64110-2499, United States § Department of Chemistry, Howard University, 525 College Street, NW, Washington, DC 20059, United States Downloaded via UNIV OF SUNDERLAND on October 5, 2018 at 13:35:11 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

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S Supporting Information *

ABSTRACT: The reaction of [ZnGe18(Hyp)6] (Hyp = Si(SiMe3)3) with Pt(PPh3)4 gives the neutral polynuclear complex of Ge9(Hyp)3 units [HypZn−Ge9(Hyp)3−Pt− Ge9(Hyp)3−ZnHyp], 1. Within 1, the central Pt atom is bound η3 to both Ge9(Hyp)3 units to which further ZnHyp units are bound again, symmetric η3, to the other side of the Ge9(Hyp)3 units, leading to the longest chain compound exhibiting Ge9(Hyp)3 units that is known to date. Dissolved crystals of 1 give a violet solution, showing an absorption maximum around 543 nm. Further UV−vis investigations on different MxGe9(Hyp)3 compounds show that the absorption maximum depends on the number of transition metal atoms bound to the Ge9(Hyp)3 unit, which is supported by TD-DFT calculations.

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to [(Hyp)3EtGe9Pd(PPh3)],11 while the reaction with the charged stannyl-decorated cluster [Ge9(SniPr3)3]− gives [Ge18Pd3(SniPr3)6]2− (Figure 2).12 In addition, the reaction of Pd(PPh3)4 with [Ge9(Hyp)3]− itself gives [PdGe18(Hyp)6]2− with a typical structure similar to all other [MGe18(Hyp)6]n− complexes (Figure 1c).6 In the current work we present [PtZn2Ge18(Hyp)8] (1), a neutral polynuclear chain compound with [Ge9(Hyp)3]− units and different transition metal atoms, as the product of the reaction of Pt(PPh3)4 with [ZnGe18(Hyp)6] (A). To the best of our knowledge, 1 is the first example of a bimetallic complex with [Ge9(Hyp)3]− ligands, exhibiting different transition metal atoms, and it is additionally the longest chain compound in this series.13

INTRODUCTION Metalloid cluster compounds1 of the general formula MnRm (n > m; M = metal like Al, Au, Sn, Ge, etc.; R = ligand, like Si(SiMe3)3 or N(SiMe3)2) are ideal model compounds for molecular entities in the gray area between molecules and the solid state.2 The chemistry of metalloid group 14 clusters is thus of central interest in main-group chemistry. In this field, the anionic metalloid cluster [Ge9(Hyp)3]−3 plays a special role, due to its high stability under inert conditions, solubility in organic solvents, and high-yield synthesis.4 Numerous subsequent reactions were performed with this exciting compound. Among them are build-up reactions to give cluster aggregates of definite composition [(Hyp) 3 Ge 9 −M− Ge9(Hyp)3]n− (n = 1, M = Cu, Ag, Au; n = 0, M = Zn, Cd, Hg, Mn)5 and even larger chain compounds such as [Ge9(Hyp)3−Cu−Ge9(Hyp)3−Cu−PPh3],6 showing the potential of [Ge9(Hyp)3]− for the synthesis of novel materials. Besides coordination, also redox chemistry can take place if the right transition metal source is used, leading, for example, to the neutral metalloid cluster Ge18(Hyp)67 or to the mono- or binuclear nickel complexes [Ni(dppe)Ge9(Hyp)3] and [{Ni(dppe)}2{Ge9(Hyp)3}][Ge9(Hyp)3]8 (Figure 1). Besides the built-up route, also cluster enlargement reactions are possible, generally by using low-valent transition metal compounds. For instance, the reaction of [Ge9(Hyp)3]− with M(CO)3(MeCN)3 gives [(Hyp)3Ge9M(CO)3]− (M = Cr, Mo, W),9 exhibiting a 10-atomic closo-cluster core. Such cluster enlargements are also very sensitive to the substituent bound to the Ge9 core as recently shown by Sevov et al., where the reaction of Pd(PPh3)4 with the neutral cluster [(Hyp)3Ge9Et]10 leads © XXXX American Chemical Society

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RESULTS AND DISCUSSION During our systematic research on metalloid Ge9R3− clusters and their derivatives, we investigated the reactivity of [ZnGe18(Hyp)6] (A) toward different reagents such as oxidants ([Ph3C]+[BF4]−) and low-valent transition metal complexes (W(CO)3(MeCN)3). Surprisingly, A turned out to be a quite inert compound, and no reactions were observed during these experiments. However, by using the metal(0) compound Pt(PPh3)4, the unexpected product [PtZn2Ge18(Hyp)8] (1) is reproducibly obtained (see Experimental Part). Thereby, in the first experiments, 1 was obtained in a one-pot reaction from presynthesized A containing an excess of ZnCl2 Received: June 25, 2018

A

DOI: 10.1021/acs.inorgchem.8b01757 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

unusual, however, are the Zn−Ge distances of 266−270 pm, being significantly longer than the Cu−Ge distances of 240 pm between the Cu(PPh3)3 fragment and the open Ge9(Hyp)3 unit in [Ge9(Hyp)3−Cu−Ge9(Hyp)3−Cu−PPh3]. The Zn− Ge distances within 1 are more in line with the Zn−Ge distances within [ZnGe18(Hyp)6], A, although there the coordination number of the central zinc atom is much larger. This is indeed an interesting structural feature as the covalent radii of Zn and Cu are very similar,14 and thus, the Ge−M distances might be similar as well. The elongation of the Zn−Ge distances in 1 by 28 pm might be explained by steric factors as the Hyp substituent is too bulky, pulling away the Zn atom from an ideal interaction with the [Ge9(Hyp)3] unit. To investigate this, we performed quantum chemical calculations on the model compounds [PtGe18(SiMe3)6(ZnMe)2] (1Me), PtGe18(Hyp)6(ZnMe)2, and {[PtGe18(Hyp)6](ZnSiH3)} (Figure S3). Comparing the calculated bond lengths with those of the model compound {[CuGe18(Hyp)6](CuMe)} (Figure S2) shows that when the methyl group is bound to either Cu or Zn, the Cu−Ge and Zn−Ge bonds differ only by 1−3 pm. However, when changing Me by SiH3, only in case of Zn is an elongation (∼10 pm) between Zn−Ge realized even with the Hyp ligand present. Thus, the difference for the elongation is due to the ligand−metal interactions along with steric effects of the Hypligand playing a minor role in 1.15 The Ge−Ge distances in the “open” faces of the Ge9 polyhedra in 1 vary between 275 and 278 pm for the Ge3 triangle coordinated to Zn (Ge1−Ge2− Ge3) and between 290 and 293 pm for the Ge3 triangle coordinated to Pt (Ge7−Ge8−Ge9). Hence, the central Pt atom causes a higher distortion in the Ge9 cores with respect to the side-coordinated Zn−Hyp units. It is also worth mentioning that the coordinations of both Zn and Pt are quite symmetric since M−Ge and Ge−Ge bond lengths are within a narrow range in contrast to those observed in the binuclear cation [{Ni(dppe)}2(Ge9(Hyp)3)]+, where the Ni− Ge distances vary from 238 to 255 pm. Formally, within the neutral cluster [PtZn2Ge18(Hyp)8] (1) the charges of its fragments can be easily assigned as “−1” for [Ge9(Hyp)3], “+1” for Zn−Hyp, and “0” for Pt leading overall to a closed shell compound. This was confirmed via quantum chemical calculations where the Bader analysis illustrated that the Ge9(Hyp)3 unit has an overall charge of nearly −1, the Zn−Me units have a charge of almost +1, and the Pt atom has a charge of 0. However, the “real” bonding situation can be more complicated. Surprisingly, 1 does not show a signal within the proton NMR spectrum, while the starting compound [ZnGe18(Hyp)6] (A) is NMR active and shows a single intense resonance at 0.39 ppm within proton NMR (THF-d8). Varying the temperature from −80 to +50 °C does not lead to changes in the NMR spectra of a THF solution of dissolved crystals of 1, which only show signals of a small amount of impurities, but no signal that belongs to 1. However, 1 is not paramagnetic, since neither room-temperature nor low-temperature EPR measurements performed in αmethyl-THF showed any signal, and thus until now we have had no simple explanation of this unusual behavior of [PtZn2Ge18(Hyp)8].16,17 The violet color of the solution of dissolved crystals of 1 together with our previous observations on other Ge9 derivatives drove us to UV−vis investigations of different intermetalloid clusters exhibiting [Ge9(Hyp)3] units. For this reason we measured the UV−vis spectra of the THF solutions

Figure 1. Schematic representation of molecular structures of different transition metal complexes with [Ge9(Hyp)3]− clusters, exhibiting different nuclearity and coordination modes: (a) [Ni(dppe)Ge 9 (Hyp) 3 ], (b) [{Ni(dppe)} 2 {Ge 9 (Hyp) 3 }] + , (c) [MGe18(Hyp)6]n− (n = 2, M = Pd; n = 1, M = Cu, Ag, Au; n = 0, M = Zn, Cd, Hg, Mn), and (d) [Ge9(Hyp)3−Cu−Ge9(Hyp)3−CuPPh3].

Figure 2. Schematic representation of germanium clusters incorporating Pd0 atoms: (a) [(Hyp)3EtGe9Pd(PPh3)] and (b) [Ge18Pd3(SniPr3)6]2−.

and Pt(PPh3)4 only. This means the only source for the Hypsubstituents attached to the Zn atoms in the final product 1 are the Hyp-substituents attached to the Ge9 cores in A. This means, under the experimental conditions, supposedly due to the presence of Pt(PPh3)4, the otherwise extremely stable compound [ZnGe18(Hyp)6], A, partially degrades to fragments, which are afterward included in the built-up reaction to form the final crystallized product 1. Consequently, due to an apparently quite elaborate reaction mechanism, the yield of 1 obtained this way is expectedly low. A more straightforward synthetic approach is to include all required fragments (A, Pt(PPh3)4, ZnCl2 and LiHyp) into the reaction mixture, which increases the yield of [PtZn2Ge18(Hyp)8] (1) reproducibly from a couple of crystals to 11−16%. Similar to [PdGe18(Hyp)6]2− and other [MGe18(Hyp)6]n− complexes in the structure of 1 (Figure 3), the Pt atom is located in the center between two Ge9(Hyp)3 units with Pt− Ge distances of 255−256 pm, which is in line with the average Pd−Ge distance of 255 pm in [PdGe18Hyp)6]2−.14 More B

DOI: 10.1021/acs.inorgchem.8b01757 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 3. Molecular structure of [PtZn2Ge18(Hyp)8] (1). Hydrogen atoms are omitted, and carbon and silicon atoms of the Hyp groups are shown as a wire presentation for clarity. Thermal ellipsoids are shown with 50% probability. Selected bond distances [pm] and angles [deg]: Pt1−Ge7, 255.20(6); Pt1−Ge8, 256.19(7); Pt1−Ge9, 256.23(7); Ge1−Ge2, 275.44(10); Ge1−Ge3, 277.31(10); Ge1−Ge4, 253.10(10); Ge1−Ge6, 253.34(10); Ge1−Zn1, 268.68(11); Ge2−Ge3, 277.48(10); Ge2−Ge4, 253.17(10); Ge2−Ge5, 253.03(10); Ge2−Zn1, 269.88(11); Ge3−Ge5, 252.92(10); Ge3−Ge6, 252.70(10); Ge3−Zn1, 266.02(10); Ge4−Ge7, 255.17(9); Ge4−Ge8, 255.41(9); Ge5−Ge8, 254.80(10); Ge5−Ge9, 255.32(10); Ge6−Ge7, 254.52(10); Ge6−Ge9, 255.22(9); Ge7−Ge8, 290.52(10); Ge7−Ge9, 292.53(9); Ge8−Ge9, 292.86(10); Ge5−Si5, 238.10(19); Ge6−Si6, 237.6(2); Zn1−Si1, 236.5(2); Ge7−Pt1−Ge8, 69.24(2); Ge1−Ge2−Ge3, 60.20(3); Si5−Ge5−Ge2, 113.83(5); Ge1− Ge6−Ge7, 82.47(3); Pt1−Ge7−Ge6, 109.09(3); Ge7−Ge8−Ge9, 60.19(2); Si1−Zn1−Ge1, 143.62(6).

of the following compounds: [ZnGe18(Hyp)6] (A), K[CuGe18(Hyp)6] (B), K[AgGe18(Hyp)6] (C), [Ni(dppe)Ge9(Hyp)3] (D), [{Ni(dppe)} 2 {Ge 9 (Hyp) 3 }][Ge 9 Hyp 3 ] (E), and [PtZn2Ge18(Hyp)8] (1) (the molecular structures of the mentioned compounds are presented in Figures 1 and 3). It turned out that many of these compounds show distinct absorptions in their spectra in contrast to the spectrum of [Ge9(Hyp)3]− itself, which shows an almost featureless UV− vis spectrum in the area above 350 nm. The absorption maxima of all mentioned compounds are listed in Table 1, and the spectra themselves (in normalized form) are shown in the Supporting Information (Figure S1).

bound to a [Ge9(Hyp)3] unit (E and 1) show an absorption maximum around 530 nm (Figure 5).

Table 1. UV−Vis Absorption Maxima for Different Transition Metal Complexes with [Ge9(Hyp)3]− Clusters

Figure 4. UV−vis spectra of mononuclear complexes of [Ge9(Hyp)3]−: [ZnGe18(Hyp)6] (A), K[CuGe18(Hyp)6] (B), K[AgGe18(Hyp)6] (C), and [Ni(dppe)Ge9(Hyp)3] (D). The spectra were recorded in THF solutions and are presented in normalized form in the range 300−600 nm.

compd

max absorbance, nm

[ZnGe18(Hyp)6] (A) K[CuGe18(Hyp)6] (B) K[AgGe18(Hyp)6] (C) [Ni(dppe)Ge9(Hyp)3] (D) [{Ni(dppe)}2{Ge9(Hyp)3}][Ge9Hyp3] (E) [PtZn2Ge18(Hyp)8] (1)

390 415 385 427a 535 543

To further understand the factors contributing to the observed optical spectra, we performed time-dependent density functional calculations on ZnGe18(SiMe3)6 (AMe) and

a

Due to the preparation procedure, the sample of [Ni(dppe)Ge 9 (Hyp) 3 ] (D) always exhibits traces of [{Ni(dppe)} 2 {Ge9(Hyp)3}][Ge9Hyp3] (E). Consequently, in the spectrum of the solution of D a weak absorbance maximum of E is observed at 535 nm.

Analyzing the different spectra revealed an interesting fact: The maximum absorption band observed for the compounds mainly depends on the number of transition metal atoms bound to a [Ge9(Hyp)3] unit rather than to the kind of the bound transition metal atom. This means all complexes where only one transition metal atom is bound to a [Ge9(Hyp)3] unit (A, B, C, D) show an absorption band around 400 nm (Figure 4), while the complexes where two transition metal atoms are

Figure 5. UV−vis spectra of polynuclear complexes of [Ge9Hyp3]− anion: [{Ni(dppe)} 2 {Ge 9 (Hyp) 3 }][G e 9 Hyp 3 ] (E) and [PtZn2Ge18(Hyp)8] (1). The spectra were recorded in THF solutions and are presented in normalized form in the range 300−600 nm. C

DOI: 10.1021/acs.inorgchem.8b01757 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 6. Theoretical UV−vis spectra and ball-and-stick representation of Zn[Ge9(SiMe)3]2 (AMe) and [PtGe18(SiMe)6(ZnMe)2] (1Me). Color representations are as follows: white = H, gray = C, yellow = Si, orange = Ge, green = Zn, and silver = Pt. Electron density and structure visualizations were rendered using ADF-GUI.19

Table 2. Contributing Orbitals for the Theoretical Energy Absorption Peaks for 1Mea

a

See Figure 6 for more information.

in 1Me are similar in origin to AMe in the 400−340 nm range, the excitations observed around 2.4 eV (500 nm) are quite different. The excitation at 2.55 eV is mainly from the occupied Kohn−Sham (KS) state 1 eV below the occupied KS-state with electron density located on the exterior Zn−R motif, with very little residing on the Ge9 core, and the atomic d-state on the Pt atom. The induced density actually resides throughout the linear motif encompassing the Zn−Ge9−Pt−Ge9−Zn unit (Table 2). At first glance, one would attribute the peak at 2.5 eV (500 nm) solely to the cluster core, having two or more transition metal atoms. However, upon closer examination of the optical spectra of AMe, there appears to be a weak transition around 2.5 eV (500 nm). Though this transition appears to

[PtGe18(SiMe3)6(ZnMe)2] (1Me). The optical spectra for AMe and 1Me are given in Figure 6, showing that AMe exhibits intense optical transitions between 3.0 and 3.5 eV (413−354 nm). In AMe, the transitions have contributions that arise from either one state below the highest occupied state (HOS) or lower-lying occupied states into a high-energy unoccupied state or the lowest unoccupied state (LUS), respectively (Table 2). Contrary to AMe, 1Me has an intense initial absorption peak at 2.55 eV (486 nm) (with a smaller peak at 2.45 eV (507 nm)) and additional excitations between 3.0 and 3.7 eV (413−344 nm). It should be pointed out that the theoretical spectra correspond very closely to the experimentally collected spectra for 1. This finding shows that although many of the transitions D

DOI: 10.1021/acs.inorgchem.8b01757 Inorg. Chem. XXXX, XXX, XXX−XXX

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Me-THF solutions at a Bruker ESP-300E spectrometer. EDX analysis was performed on solid samples with a HITACHI SU8030. UV−vis spectra were recorded on T60 UV−vis spectrophotometer in quartz cuvettes with a concentration of ca. 2 × 10−5 mol/L with THF as a blank sample. [ZnGe18(Hyp)6] (A), K[CuGe18(Hyp)6] (B), K[AgGe18(Hyp)6] (C), [Ni(dppe)Ge9(Hyp)3] (D), and [{Ni(dppe)}2{Ge9(Hyp)3}][Ge9Hyp3] (E) were synthesized via published procedures using KGe9(Hyp)3 as the germanium source. For the UV−vis experiments, the crystalline compounds were dissolved in THF. Synthesis of [PtZn2Ge18Hyp8] (1). Initial Experiments. For the first time, 1 was obtained in a small amount (few crystals) as a product of the reaction between presynthesized [ZnGe18(Hyp)6] and Pt(PPh3)4 after workup procedures. ZnCl2 (40 mg, 0.30 mmol, 6-fold excess approximately) was stirred together with K[Ge9(Hyp)3] (200 mg, 0.14 mmol) in toluene with a few drops of THF for 1 day which led to complete conversion of the starting [Ge9(Hyp)3]− anions to [ZnGe18(Hyp)6] according to 1H NMR. Afterward, the solvent was removed, and the obtained solid product was used as-is for the next step. Pt(PPh3)4 (170 mg, 0.14 mmol, 2-fold excess based on the composition of 1) was added to it, and the mixture was stirred for 1 week in THF, which led to a complete dissolution of somewhat insoluble reagents and a change in color from light-red to deep redviolet. After workup procedures (drying, washing with pentane, extracting by THF, redissolving of obtained extract in toluene, and slow crystallizing at +6 °C), a small amount of orange crystals suitable for X-ray analysis were obtained. The notable feature of these crystals is that on dissolution in THF they give a violet and not an orange solution. Established Synthetic Procedure. In a more convenient way with a higher yield, 1 can be obtained as follows. [ZnGe18(Hyp)6] (150 mg, 0.05 mmol) and Pt(PPh3)4 (130 mg, 0.10 mmol) were mixed in THF and stirred for 1 day. Afterward, ZnCl2 (14 mg, 0.10 mmol) and LiHyp (26 mg, 0.10 mmol) were added to the reaction mixture, and the clear dark red-violet solution was kept for 2 weeks in THF. Afterward, the solvent was removed, and the crude product was redissolved in toluene; 1 was slowly crystallized at +6 °C. The estimated total amount of crystals obtained from several batches is 20−30 mg (11−16% yield based on [ZnGe18(Hyp)6] used). EDX Measurements. [PtZn2Ge18(Hyp)8] (1) was always obtained in the form of very small air-sensitive crystals with a surface contaminated by excess of ZnCl2; therefore, precise EDX measurements of its elemental composition were impossible. However, the atomic ratio of Pt:Ge is always around 1:20 on several measured points, and after subtraction of the ZnCl2 formula unit for the ZnCl2 impurity, a reasonable elemental composition of Pt/Zn/Ge = 1:2.5:20 results which is roughly in agreement with the well-defined crystallographic structure. X-ray Structural Characterization. Crystals were mounted on the diffractometer at 150 K. The data were collected on a Bruker APEX II DUO diffractometer equipped with an IμS microfocus sealed tube and QUAZAR optics for monochromated Mo Kα radiation (λ = 0.71073 Å) and equipped with an Oxford Cryosystems cryostat. A semiempirical absorption correction was applied using the program SADABS. The structure was solved by direct methods and refined against F2 for all observed reflections. Programs used include SHELXS and SHELXL20 within the Olex2 program package.21 Data for [PtZn2Ge18(Hyp)8], 1, follow: PtGe18Zn2Si32C72H216, M = 3613.76 g mol−1, crystal dimensions 0.173 × 0.151 × 0.033 mm3, space group P1̅, a = 15.4781(6) Å, b = 15.6368(6) Å, c = 18.1470(7) Å, α = 76.544(2)°, β = 86.842(2)°, γ = 80.315(2)°, V = 4210.1(3) Å3, Z = 1, ρcalc = 1.425 g cm−3, μMo = 4.519 mm−1, 2Θmax = 52.852°, 49 710 reflections measured, 17 240 independent reflections (Rint = 0.0583). Absorptions correction details follow: semiempirical (min/max transmission 0.588/0.745), R1 (I ≥ 2σ) = 0.0518, wR2 (all) = 0.1202, Bruker APEXII diffractometer (Mo Kα radiation (λ = 0.71073 Å), 150 K).

originate from low-lying occupied states into the LUMO, similar to 1Me, the frequency of this transition is less than 0.001 eV, which is negligible and may explain its absence from experimental observations. However, in 1Me this transition becomes quite intense and observable in the experiment. The increased intensity of the peak observed around 2.5 eV (500 nm) suggests that if an assembly of Ge9(Hyp)3 contains more than one transition metal atom, presumably weak optical signatures become enhanced. It is interesting to note the electron density for various electron transitions from occupied to unoccupied KS-states. While it may be intuitive to describe transitions being from metal-to-ligand (MLCT) or even (metal) core-to-ligand as in the cases of organometallics and larger metalloid nanoparticles,18 this description may not fit the current system. Compound 1 can be viewed as a metalloid assembly with three distinct parts: (1) Ge9Hyp3, (2) Zn−R, and (3) a linking atom (Pt). As evidenced in Table 2 and Table S1, the electron density could be located on each individual building block or delocalized unilaterally across the entire metal core (without residing on the R-unit) as in the case of the highest occupied state (HOS). For example, in 1Me the peak at 3.0 eV (413 nm) originates from the HOS-1 with density residing unilaterally across the PtZn2Ge18 metal core to the highest occupied KSstate (Table 2), while the induced KS-state has density on the two Ge9-cores. The electron density for the theoretical peak observed at 3.3 eV (376 nm) involves one state with electron density on Ge9 cores and a state with electron density throughout the metal core and some density on the ligand (induced). The most intense peak at 3.6 eV (344 nm) involves Ge9 and Pt, with the induced density being located primarily on the Ge9-cores. However, if the system is modeled with the full Hyp-ligand, peaks may become broader and more intense while involving multiple charge transfer states. While the change in electron density may not be observed immediately in the HUS or LUS of Hyp containing structures when compared to 1Me, the change can be seen in other states (Figure S3).

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SUMMARY In summary, the neutral polynuclear bimetallic complex of Ge 9(Hyp) 3 units [HypZn−Ge9 (Hyp) 3−Pt−Ge9 (Hyp)3 − ZnHyp], 1, was synthesized via the reaction of [ZnGe18Hyp6] (A), ZnCl2, and Pt(PPh3)4, indicating degradation of A under the experimental conditions. Experimental and computational UV−vis investigations of 1 and other known Mn[Ge9(Hyp)3]m complexes show that the position of absorbance maxima largely depends on the number of transition metal atoms bound to a Ge9(Hyp)3 unit, being observed around 400 nm for mononuclear and around 530 nm for polynuclear complexes. Though 1 exhibits unusual structural (long Zn−Ge bonds) characteristics, its interesting magnetic (absence of 1H NMR and EPR spectra) features and polynuclear configuration warrant future investigation.

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EXPERIMENTAL PART

General Considerations. Commonly used abbreviations follow: THF = tetrahydrofuran, Hyp = Si(SiMe3)3. All reactions were performed under nitrogen atmosphere using Schlenk techniques. THF and toluene were dried over sodium and pentane over CaH2. All organic solvents were freshly distilled under a nitrogen atmosphere prior to use. THF-d8 solutions of 1 were used to obtain NMR spectra on Bruker DRX-250 and Bruker AVII+400 spectrometers at different temperatures (+50 to −80 °C). EPR data were measured in frozen E

DOI: 10.1021/acs.inorgchem.8b01757 Inorg. Chem. XXXX, XXX, XXX−XXX

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COMPUTATIONAL DETAILS

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and controlled synthesis of precise thiolate-gold nanoclusters. Coord. Chem. Rev. 2016, 329, 1−15. (d) Jin, R.; Zeng, C.; Zhou, M.; Chen, Y. Atomically Precise Colloidal Metal Nanoclusters and Nanoparticles: Fundamentals and Opportunities. Chem. Rev. 2016, 116, 10346− 10413. (3) (a) Schnepf, A. [Ge9{Si(SiMe3)3}3]−: A Soluble Polyhedral Ge9 Cluster Stabilized by Only Three Silyl Ligands. Angew. Chem. 2003, 115, 2728−2729. Schnepf, A. Angew. Chem., Int. Ed. 2003, 42, 2624− 2625. (b) Li, F.; Sevov, S. C. Rational Synthesis of [Ge9{Si(SiMe3)3}3]− from Its Parent Zintl Ion Ge94−. Inorg. Chem. 2012, 51, 2706−2708. (4) Kysliak, O.; Schnepf, A. Metalloid Germanium Clusters as Starting Point for New Chemistry. In Elsevier Reference Module in Chemistry, Molecular Sciences and Chemical Engineering; Reedijk, J., Ed.; Elsevier: Waltham, MA, 2017. (5) (a) Schenk, C.; Schnepf, A. [AuGe18{Si(SiMe3)3}6]−: A Soluble Au−Ge Cluster on the Way to a Molecular Cable? Angew. Chem., Int. Ed. 2007, 46, 5314−5316. Schenk, C.; Schnepf, A. Angew. Chem. 2007, 119, 5408−5410. (b) Schenk, C.; Henke, F.; Santiso-Quinones, G.; Krossing, I.; Schnepf, A. [Si(SiMe3)3]6Ge18M (M = Cu, Ag, Au): Metalloid cluster compounds as unusual building blocks for a supramolecular chemistry. Dalton Trans 2008, 4436−4441. (c) Henke, F.; Schenk, C.; Schnepf, A. [Si(SiMe3)3]6Ge18M (M = Zn, Cd, Hg): Neutral metalloid cluster compounds of germanium as highly soluble building blocks for a supramolecular chemistry. Dalton Trans 2009, 9141−9145. (d) Geitner, F. S.; Fässler, T. F. Introducing Tetrel Zintl Ions to N-Heterocyclic Carbenes − Synthesis of Coinage Metal NHC Complexes of [Ge9{Si(SiMe3)3}3]−. Eur. J. Inorg. Chem. 2016, 2016, 2688−2691. (e) Geitner, F. S.; Giebel, M. A.; Pöthig, A.; Fässler, T. F. N-Heterocyclic Carbene Coinage Metal Complexes of the Germanium-Rich Metalloid Clusters [Ge9R3]− and [Ge9RI2]2‑ with R = Si(iPr)3 and RI= Si(TMS)3. Molecules 2017, 22, 1204. (6) Li, F.; Sevov, S. C. Coordination of Tri-Substituted Nona− Germanium Clusters to Cu(I) and Pd(0). Inorg. Chem. 2015, 54, 8121−8125. (7) Kysliak, O.; Schrenk, C.; Schnepf, A. The Largest Metalloid Group 14 Cluster, Ge18[Si(SiMe3)3]6: An Intermediate on the Way to Elemental Germanium. Angew. Chem. 2016, 128, 3270−3274. Kysliak, O.; Schrenk, C.; Schnepf, A. Angew. Chem., Int. Ed. 2016, 55, 3216− 3219. (8) Kysliak, O.; Schrenk, C.; Schnepf, A. Reactivity of [Ge9{Si(SiMe3)3}3]− towards transition metal M2+ cations: coordination and redox chemistry. Chem. - Eur. J. 2016, 22, 18787−18793. (9) (a) Schenk, C.; Schnepf, A. {Ge9[Si(SiMe3)3]3Cr(CO)5}− and {Ge9[Si(SiMe3)3]3Cr(CO)3}−: The metalloid cluster compound {Ge9[Si(SiMe3)3]3}− as a flexible ligand in coordination chemistry. Chem. Commun. 2009, 3208−3210. (b) Henke, F.; Schenk, C.; Schnepf, A. [Si(SiMe3)3]3Ge9M(CO)3− (M = Cr, Mo, W): Coordination Chemistry with metalloid Clusters. Dalton Trans 2011, 40, 6704−6710. (10) Li, F.; Sevov, S. C. Synthesis, Structures, and Solution Dynamics of Tetrasubstituted Nine-Atom Germanium Deltahedral Clusters. J. Am. Chem. Soc. 2014, 136, 12056−12063. (11) Li, F.; Munoz-Castro, A.; Sevov, S. C. [(Me3Si)Si]3EtGe9Pd(PPh3), a Pentafunctionalized Deltahedral Zintl Cluster: Synthesis, Structure, and Solution Dynamics. Angew. Chem. 2016, 128, 8772− 8775. Li, F.; Munoz-Castro, A.; Sevov, S. C. Angew. Chem., Int. Ed. 2016, 55, 8630−8633. (12) Perla, L. G.; Sevov, S. C. A Stannyl-Decorated Zintl Ion [Ge18Pd3(SniPr3)6]2−: Twinned Icosahedron with a Common Pd3Face or 18-Vertex Hypho-Deltahedron with a Pd3-Triangle Inside. J. Am. Chem. Soc. 2016, 138, 9795−9798. (13) In case of metalloid tin clusters, a comparable long bimetallic chain compound HypAu−Sn9(Hyp)3−Au−Sn9(Hyp)3−AuHyp is known. Binder, M.; Schrenk, C.; Block, T.; Pöttgen, R.; Schnepf, A. [Hyp-Au-Sn9(Hyp)3-Au-Sn9(Hyp)3-Au-Hyp]−: The longest intermetalloid chain compound of tin. Chem. Commun. 2017, 53, 11314− 11317.

Quantum chemical calculations for initial relaxation of species were carried out using the Amsterdam Density Functional (ADF) package.19 To account for exchange and correlation, the BP86 functional was employed.22 The triple-ζ polarized basis set23 was used to describe the atoms with a small frozen core. Relativistic effects for transition metal atoms was taken into account using the scalar zerothorder regular approximation.24 Starting configurations were determined using the crystal structures for compounds. Visualizations of electron density and relaxed structures were performed using the ADF-GUI.19 The theoretical optical spectra were obtained using the linear response time-dependent density functional module as implemented in GPAW using the PBE functional as in our previous study.25 The role of THF solvent on the theoretical spectra is negligible on the basis of our previous study.25 S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b01757. UV−vis spectra and additional computational details, (PDF) Accession Codes

CCDC 1833485 contains 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 Authors

*E-mail: [email protected]. Phone: +1 (202) 8066900. *E-mail: [email protected]. Phone: +49 (7071) 29-76635. Fax: +49 (7071) 28-2436 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are grateful to the Deutsche Forschungsgemeinschaft (DFG) for financial support. The computation for this work was performed on the high-performance computing infrastructure provided by Research Computing Support Services and in part by the National Science Foundation under grant number CNS-1429294 at the University of Missouri, Columbia, MO. We thank Dr. Claudio Schrenk for helpful discussions. This paper is dedicated to Professor Dietmar Stalke on the occasion of his 60th birthday.

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REFERENCES

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DOI: 10.1021/acs.inorgchem.8b01757 Inorg. Chem. XXXX, XXX, XXX−XXX