Crystal structures and Hirshfeld surface analyses of tetrakis(4,5-dihydrofuran-2-yl)silane and tetrakis(4,5-dihydrofuran-2-yl)germane

The crystal structures of a dihydrofurylsilane and a dihydrofurylgermane are reported. Hirshfeld surface analyses were performed to investigate the intermolecular interactions.


Structural commentary
The molecular structure of 1 is shown in Fig. 1 and selected bond lengths and angles of the solid-state structure are shown in Table 1. There are two molecules in the asymmetric unit. The listed bond lengths of the Si-C(DHF) links are all in a comparable range. In addition, the bond lengths are consistent with the characteristic Si-C bond length (Allen et al., 1987). The C-Si-C bond angles deviate from the ideal value of 109.47 and indicate a slightly distorted tetrahedron. This has already been described in related compounds by Strohmann and co-workers (Krupp et al., 2020;Schmidt et al., 2022). This slight distortion is possibly due to the packing in the solid state. The bond lengths of the C C bonds within the dihydrofuranyl substituent show agreement with bond lengths known in the literature. The C-C single bond between the two sp 3 carbon atoms shows a clear deviation from the median known in literature, and is nearly in the lower quartile. This was also previously described by Strohmann and co-workers (Krupp et al., 2020;Schmidt et al., 2022). The DHF rings of the structure do not show complete planarity and have the r.m.s deviations shown in Table 2. The largest deviation of an atom from the planar position is shown by the sp 3 carbon atom C28, which is located next to the oxygen atom O7. This has also been reported for comparable structures (Schmidt et al., 2022).
In addition, Table 2 shows the dihedral angles between the normals of two rings.
The molecular structure of 2 is shown in Fig. 2. There are two molecules in the asymmetric unit and selected bond lengths and angles are given in Table 3. The Ge-C bonds are in a comparable range and are consistent with similar bond lengths in the literature (Lazraq et al., 1988). As already described for structure 1, the germane 2 also shows a slight deviation from the ideal tetrahedral value for the C-Ge-C bond angles, which can also be explained by the packing in the solid state. Likewise, the bond lengths of the C C groups within the dihydrofuranyl rings show consistency with bond lengths known in the literature, as well as the C-C bond between two sp 3 carbon atoms showing similar peculiarities as previously described (Krupp et al., 2020;Schmidt et al., 2022 The molecular structure of compound 1 with displacement ellipsoids drawn at the 50% probability level.

Figure 2
The molecular structure of compound 2 with displacement ellipsoids drawn at the 50% probability level. Table 1 Selected geometric parameters (Å , ) for 1.  Table 3. Compared to 1, the deviations in 2 are smaller and, again, the sp 3 carbon atom C28, which is located next to O7, shows the highest deviation. However, this does not apply to the C21-C24/O6 ring as this has a very low r.m.s. deviation and C21 shows the highest deviation. The dihedral angles between the normals of two rings are listed in Table 4.

Supramolecular features
In order to quantify the intermolecular interactions in the crystal structure, a Hirshfeld surface analysis was carried out, generated by CrystalExplorer21 (Spackman et al., 2021). The Hirshfeld surface of 1 is shown in Fig. 3, where the red areas represent closer interactions between adjacent atoms. The Hirshfeld surface is mapped over d norm , in the range À0.11 to 1.37 a.u. The distribution of the different interactions is illustrated by the two-dimensional fingerprint plots (Fig. 4)  Notes: (a) compared to C1-C4/O1; (b) compared to C17-C20/O5. Table 3 Selected geometric parameters (Å , ) for 2.
For the Hirshfeld surface analysis of 2, a surface mapped over d norm in the range À0.15 to 1.33 a.u. was used (Fig. 6). The distribution of the various interactions is illustrated by the two-dimensional fingerprint plots (Fig. 7). The distribution of the interactions is very similar and minimally larger for HÁ Á ÁH (71.6%) than for 1. The interactions between H31BÁ Á ÁH31B i at 2.17 (4) Å and H7BÁ Á ÁH7B i [symmetry code: (i) Àx, Ày, Àz] at 2.20 (4) Å are visible as red spots and could be identified as close interactions by the Hirshfeld surface. The contribution of the van der Waals interactions is slightly lower at 10.0%. The interaction C32Á Á ÁH4A ii [symmetry code: (ii) 1 2 À x, 1 2 + y, 1 2 À z] at 2.79 (2) Å could also be detected on the Hirshfeld surface. As in the case of 1, interactions of the form HÁ Á ÁO could be determined, which contribute 18.  A part of the crystal packing of compound 1 via hydrogen bonds C27-H27BÁ Á ÁO3 iii and C31-H31AÁ Á ÁO4 in the (101) plane. C-HÁ Á ÁO hydrogen bonds are shown as dashed blue lines. [Symmetry codes: (iii) À 1 2 + x, 1 2 À y, 1 2 + z].
The reaction solution was stirred for 1 h at rt. Tetrachlorogermane (2.00 g, 9.33 mmol, 1.00 eq.) was added at 213 K and the reaction solution was stirred for 1 h. The resulting solid was separated by inert filtration. The obtained solution was concentrated in vacuo and crystallized at 243 K. The solvent was removed, and the solid was washed with cold diethyl ether. The product tetrakis(4,5-dihydrofuran-2-yl)germane (2)

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.