[GeRu6(CO)18HI]: A Germanium‐Centered Ruthenium Carbonyl Cluster with Aromatic Ring Current

Abstract The carbonyl cluster compound [GeRu6(CO)18HI] is unique in regard to its structure and bonding with a GeRu6 cluster core, a planar GeRu4HI unit, extensive multi‐center bonding, and an aromatic ring current similar to benzene (9‐10 nA T−1). The open‐shell cluster core is a Ge‐centered five‐membered Ru4(Ru2) ring with CO ligands and an additional H and I atom, each bridging two Ru atoms on opposite sides of the cluster core. The compound is prepared at 130 °C in a weakly‐coordinating ionic liquid.


Analytical Techniques
Single-crystal X-ray structure analysis.For single crystal structure analysis, suitable crystals of [GeRu6(CO)18HI] were selected, covered by inert-oil (perfluoropolyalkylether, ABCR, Germany), and placed on a micro gripper (MiTeGen, USA).Data collection was performed at 200 K on an IPDS II image-plate diffractometer (Stoe, Germany) using Mo-Kα radiation (λ = 0.71073 Å, graphite monochromator) as well as at 180 K on a Stoe StadiVari Diffractometer with Euler geometry (Stoe)   using Ga-Kα radiation (λ = 1.34013Å, graded multi-layer mirror as monochromator).S2] Using Olex2 [S3] , the structure was solved with the ShelXT [S4] structure solution program using Intrinsic Phasing and refined with the ShelXL [S4] refinement package using least squares minimization.All non-hydrogen atoms were refined anisotropically.The bridging H-atom was located directly from the maximum residual density, assigned a fixed thermal displacement parameter and its coordinates were refined freely.Detailed information on crystal data and structure refinement are listed in Table S1.DIAMOND was used for all illustrations [S5] Further details of the crystal structure investigation may be obtained from the joint CCDC/FIZ Karlsruhe deposition service on quoting the depository number CSD-No.2260888.
Energy dispersive X-ray spectroscopy (EDXS) was performed using an Ametec EDAX mounted on a Zeiss SEM Supra 35 VP scanning electron microscope (Zeiss, Germany).The samples were prepared in the glove-box by selecting single crystals that were fixed on a conductive carbon pad on an aluminum sample holder.The samples were handled under inert conditions during transport and sample preparation.
The samples were measured as pellets in KBr.Thus, 300 mg of dried KBr and 0.5-1.0mg of the sample were carefully pestled together and pressed to a thin pellet.
Optical spectroscopy (UV-Vis) of powder samples was recorded on a Shimadzu UV-2700 spectrometer (Shimadzu, Japan), equipped with an integrating sphere, in a wavelength interval of 250-800 nm against BaSO4 as reference.
Nuclear magnetic resonance (NMR) spectroscopy. 1H-NMR spectroscopy was performed on a Bruker Avance II, operating at 300 MHz (Bruker, Germany).For this purpose, a saturated solution of [GeRu6(CO)18HI] in CDCl3 (2 mg/mL; compare Table S2).The resulting solution was analyzed directly after preparation.Chemical shifts were referenced internally using signals of the residual protio solvent ( 1 H) were reported relative to tetramethylsilane.All NMR spectra were measured at 298 K, unless otherwise specified.

Mass spectrometry (MS).
Electro spray ionization (ESI) mass spectra were recorded on a Q Exactive (Orbitrap) mass spectrometer (Thermo Fisher Scientific, San Jose, CA, USA) equipped with a HESI II probe at a capillary temperature of 320 °C.
The FT resolution was set to 140,000.The instrument was calibrated in the m/z range 128-1800 with a mass deviation of less than 1 ppm.All spectra were recorded in the negative mode.The sample was prepared in d 8 toluene as solvent in a glove box under argon at a concentration of about 0.1 mg/mL.The flow rate was set to 5 µL/min.
[GeRu6(CO)18HI].80 mg (0.1379 mmol) of GeI4, 88.2 mg (0.1379 mmol) of Ru3(CO)12 and 1 mL of [BMIm][OTf] were heated under argon in a sealed glass ampoule for 96 h at 130 °C.After cooling to room temperature with a rate of 1 K/h, the title compound crystallizes as orange to red crystals and was obtained as a side phase (about 20% yield) together with a black powder of [Ru(CO)4]n (Figure S1).The title compound is highly sensitive to air and moisture and needs to be handled with strict inert conditions.Since [Ru6GeHI(CO)18] could not be obtained as a pure phase, crystals for characterization were manually separated from the side phase.

Structural Characterization
Structural data and refinement details are summarized in Table S1.The unit cell of the title compound is displayed in Figure S2.Moreover, the molecular structure of [GeRu6(CO)18HI] is shown with different views (Figure S3).Finally, the longranging distances between the molecular units of [GeRu6(CO)18HI] are displayed in Figure S4.Accordingly, the shortest intermolecular H-I distances are 654.3(7)and 669.7(7) pm (Figure S4a,b).The shortest intermolecular Ru-Ru distances are 608.7(1)and 613.4(1) pm (Figure S4c).

Spectroscopic Characterization
To verify the red color of the title compound, UV-Vis spectroscopy was performed (Figure S5).Here strong absorption is observed below 500 nm, which is in accordance with the red color of single crystals (see main paper: Figure 1b).Continuous-wave electron paramagnetic resonance (CW-EPR) spectroscopy was performed in toluene.Here, no specific signal could be detected (Figure S7).Accordingly, [GeRu6(CO)18HI] does not exhibit any electron spin due to unpaired Table S2.Solubility of [GeRu6(CO)18HI] in different solvents at room temperature.In addition to the large-scale FT-IR spectrum (1300-600 cm -1 ) shown in the main manuscript (Figure 3c), the full spectrum is shown here in Figure S9.
S15] TURBOMOLE's quadrature grid 5 was used and weight derivatives were considered when computing the analytic nuclear gradients.The geometry optimizations were performed in C2v symmetry, the self-consistent-field convergence threshold (scfconv) was set to 10 −10  h , and an equilibrium geometry was considered to be converged when the energy was converged to within 10 −9  h and the norm of the Cartesian gradient vector was less than 10 −6  h / 0 .All equilibrium geometries were confirmed to be minima on the potential-energy hypersurface by computing (with TURBOMOLE's AOFORCE module) the harmonic vibrational frequencies, which were all real.
Harmonic vibrational frequencies of the three vibrations that involve the H atom are given in Table S3.Anharmonic corrections were obtained by computing potential energy curves along the three normal modes that involve the H atom at the PBE0-D4 and B3LYP-D3(BJ) levels (Table S4).To illustrate the procedure, three potential energy curves were obtained from PBE0-D4 calculations (Figure S10).
Interatomic distances of the equilibrium geometries of [GeRu6(CO)18HI] using various functionals are listed in Table S5.
Wiberg bond indices obtained in the def2-TZVP basis are listed in Table S6.Computed 1 H chemical shift (in ppm) for [GeRu6(CO)18HI] were calculated relative to tetramethylsilane and are listed in Table S7.
Magnetically induced current densities were calculated with GIMIC [S16] from the magnetic response density obtained with TURBOMOLE's module [S17] for chemical shielding constants at level PBE0/def2-TZVP.The integration boundaries for the currents were obtained from the zero-crossings of the current profiles; the outer boundaries for plane 1 and plane 2 were set to 8 a.u.(see main paper: Figure 5).Furthermore, contour plots of the -aromatic system are shown in Figure S11.
Table S3.Computed harmonic vibrational frequencies ( e in cm −1 ) of vibrations involving the H atom of the [GeRu6(CO)18HI] cluster in C2v symmetry.Also given is the computed IR intensity in km/mol.Four Ru atoms lie in the y,z-plane, two Ru atoms lie in the x,z-plane.The def2-TZVP basis was used.Table S5.Interatomic distances (in pm) of the equilibrium geometries of the [GeRu6(CO)18HI] cluster, optimized in the def2-TZVP basis set at the DFT level using various functionals.
Table S7.Computed 1 H chemical shift (in ppm) of the [GeRu6(CO)18HI] cluster in the def2-TZVP basis set at the DFT level using various functionals.Relative to tetramethylsilane, computed with the MPSHIFT module of TURBOMOLE.

Figure S2 .
Figures of merit

Figure S3 .
Figure S3.Molecular structure of [GeRu6(CO)18HI] with top view and side view.

Table S4 .
Anharmonic corrections to the vibrational frequencies as computed at the PBE0-D4 and B3LYP-D3(BJ) levels.The def2-TZVP basis was used.