*4.4. Reaction of the Crude Product from Section 4.2 with AgNO<sup>3</sup> in Acetone–Water*

A solution of the product mixture obtained in 4.2. (1.53 g) in acetone (55 mL) was treated with a solution of AgNO<sup>3</sup> (2.69 g, 15.8 mmol) in water (15 mL). Stirring was continued at r.t. with exclusion of light for 4 days. After removal of the solvents in vacuo, the residue was taken up in the minimum amount of MeCN and placed on top of a silica gel column. MeCN: toluene 3:7 eluted a first fraction, while elution with MeCN: toluene 1:1 produced a second fraction. After evaporation to dryness, yellow-brown powders were obtained. Both fractions were examined by NMR spectroscopy. The first turned out to be Ag[C5H(CN)4], Figures S5 and S6, while the second was identified as **B'** (=**4**) (Figure S7). Recrystallization of the second fraction from toluene/acetonitrile produced X-ray quality crystals.

Compound **4**: <sup>13</sup>C-NMR (101 MHz, DMSO-d<sup>6</sup> ): *δ* = 128.0 (C–C), 115.2, 114.6 (2 × CN), 99.9, 96.9 (2 × CCN), MS: MALDI(-): *m/z* = 329.1 ([HC18N<sup>8</sup> - ]). IR: [cm−<sup>1</sup> ]: *ν* = 2218 vs, 1465 m, 1437 m, 730 vs, 695 m (+ many weak and very weak absorptions between 1900 and 750); EA: calc. for Ag2C18N<sup>8</sup> × 1.68 toluene × MeCN: C 51.57, N 17.03 H 2.24; found: C 51.54, N 16.97 H 2.29.

## *4.5. Reaction of* **1** *with Catalytic Amounts of [Ru(C5H5)Cl(PPh3)2] and NEt4Br*

A solution of **1** (2.0 g, 10.1 mmol) in anhydrous MeCN (50 mL) was added to a suspension of [Ru(C5H5)Cl(PPh3)2] (0.030 g, 4.1 µmol) in anhydrous MeCN (5 mL) at 0 ◦C within two hours. Then, water (20 mL) was added first and then solid NEt4Br (6.00 g, 28.8 mmol). The obtained suspension was filtered, and the residue taken up in the minimum amount of MeCN. Chromatography on silica gel using MeCN: toluene 1:9 as eluent produced two major fractions. NMR spectroscopy identified the first fraction as NEt4[C5H(CN)4]. The second fraction produced after evaporation a brown powder (0.40 g) which contained, according to its mass spectra, compound **5**. Recrystallization from MeCN/toluene produced a small number of crystals of low quality (pseudomerohedral twins).

### *4.6. Reaction of* **4** *with KCl in MeOH*

A suspension of **4** (68 mg, 0.125 mmol) in methanol (10 mL) was treated with a solution of KCl (4.7 mg, 0.063 mmol) in methanol (5 mL). The mixture was stirred at room temperature under the exclusion of light for 8 h and the solvent was evaporated to a volume of 1 mL. The solution was purified in a syringe filter before the product was precipitated with dichloromethane as a colorless solid (23 mg). NMR spectra showed the presence of small amounts of a [C5H(CN)4] salt besides an octacyanofulvalenediide (presumably with K <sup>+</sup> as cation, Figures S8 and S9). The compound was recrystallized from MeCN/toluene by vapor diffusion at 25 ◦C to yield X-ray quality crystals that were also subjected to further characterization.

Compound **6**: <sup>13</sup>C-NMR (101 MHz, DMSO-d<sup>6</sup> ): *δ* = 128.0 (C–C), 114.6, 113.9 (2 × CN), 99.9, 96.9 (2 <sup>×</sup> CCN). MS (MALDI\* ): *m*/*z* = 328.1 (C18N<sup>8</sup> <sup>−</sup>). calcd. for K2C18N<sup>8</sup> × 0.49 toluene × 2 H2O:: C 52.79, N 22.98, H 1.64; found C 52.26, N 23.00, H 2.21.

### *4.7. Crystal Structure Determinations*

All crystals were measured on a BRUKER D8VENTURE system. Compound **4** was obtained as twins. Refinement was possible using a HKLF 5 file with a BASF factor of ca. 0.25. Compound **5** also showed twinning (pseudomerohedral), which could, however, not be properly resolved. Still, refinement was possible. The experimental details of the structure determinations are collected in Table 5. The software package WINGX [35] was used for structure solution (SHELXT, [36], refinement (SHELXL 2018/3, [37]), evaluation (PLATON, [38]), and graphical representation (ORTEP3 and MERCURY [35]). Carbon-bound hydrogen atoms were treated with a riding model using the AFIX command of SHELXL.

*Inorganics* **2023**, *11*, 71


**Table 5.** Experimental details of the crystal structure determinations.

**Supplementary Materials:** The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/inorganics11020071/s1, Table S1: Important bond parameters of compound **4** (room-temperature determination); Figure S1: <sup>1</sup>H-NMR (400 MHz, DMSO-d<sup>6</sup> ) of the crude reaction product of reaction 4.2; Figure S2: <sup>13</sup>C{1H}-NMR (101 MHz, DMSO-d<sup>6</sup> ) of the crude reaction product of reaction 4.2.; Figure S3: <sup>1</sup>H-NMR (400 MHz, DMSO-d<sup>6</sup> ) of the crude reaction product of reaction 4.3; Figure S4: <sup>13</sup>C{1H}-NMR (101 MHz, DMSO-d<sup>6</sup> ) of the crude reaction product of reaction 4.3; Figure S5: <sup>1</sup>H-NMR (400 MHz, DMSO-d<sup>6</sup> ) of the first chromatography fraction of reaction 4.4.; Figure S6: <sup>13</sup>C{1H}-NMR (101 MHz, DMSO-d<sup>6</sup> ) of the first chromatography fraction of reaction 4.4; Figure S7: <sup>13</sup>C{1H}-NMR (101 MHz, DMSO-d<sup>6</sup> ) of the second chromatography fraction of reaction 4.4; Figure S8: <sup>1</sup>H-NMR (400 MHz, DMSO-d<sup>6</sup> ) of the purified product of reaction 4.6; Figure S9: <sup>13</sup>C{1H}-NMR spectrum (101 MHz, DMSO-d<sup>6</sup> ) of the purified product of reaction 4.6; Figure S10: The infinite 1D chain in the structure of compound **1**; Figure S11: ORTEP3 plot of the asymmetric unit of **4**, at r.t; Figure S12: Two views of the pore structure of **4**, generated by virtual removing the disordered toluenes; Figure S13: Two packing views of compound **4**; Figure S14: ORTEP3 view of the zig-zag chain of face-fused KN4O<sup>2</sup> octahedra along the *x* direction; Figure S15: Packing plots of compound **6**, watched along *c*; Figure S16: Packing plot of compound **6**, watched along *b*; Figure S17: HOMO and LUMO of compound **1**, as calculated with *CrystalExplorer*; Figure S18: Electron density plot of compound **1**; Figure S19: Two views of the electrostatic potential distribution in compound **1**.

**Author Contributions:** Conceptualization, P.N. and K.S.; methodology, P.N.; software, K.S.; validation, P.N., and K.S.; formal analysis, P.N.; investigation, P.N. and Y.K.; resources, K.S.; data curation, K.S.; writing—original draft preparation, P.N. and Y.K.; writing—review and editing, K.S.; visualization, K.S. and P.N.; supervision, K.S.; project administration, K.S.; funding acquisition, Y.K. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Data Availability Statement:** CCDC-2236238-2236242 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, by emailing data\_request@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: +44-1223336033.

**Acknowledgments:** We thank T. Klapötke for providing the NMR and D. Fattakhova-Rohlfing for providing the CV instrumentation. We also acknowledge P. Mayer for performing the X-ray diffraction measurements and F. Zoller for performing the CV experiments.

**Conflicts of Interest:** The authors declare no conflict of interest.

### **References**


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