4.5.2. Crystallographic Features of RIV

Visualization of the RIV crystal structure displayed the presence of (0 1 1) and (1 0 2) as the primary and secondary slip planes, respectively (Figure 9). The plane (0 1 1) is termed as the "primary slip plane" as it has comparatively larger d-spacing (4.4850 Å) than the (1 0 2) plane (3.8752 Å), which is

considered as the "secondary slip-plane" (Table 4). As shown in Figure 9, the surface topology of (011) is a flat layer, while that of (1 0 2) is corrugated or zigzag layers. Similar to RIV-MAL Co, the RIV crystal structure possesses intermolecular 1D H-bonding between RIV molecules.

**Figure 9.** Crystal structure evaluation of RIV indicating the presence flat layers of RIV molecules with 1D hydrogen bonding along (0 1 1) plane (**a**), and corrugated layers along (1 0 2) plane (**b**).

On the *Eatt* calculations, the lower attachment energies (close to the least *Eatt*) were observed for the two planes, i.e., (0 1 1) with *Eatt* = −44.2 kcal/mol, and (0 0 1) with *Eatt* = −39.9 kcal/mol (Table 3). This indicates the possibility of two primary active slip planes. However, when (0 0 1) plane is visualized using Mercury software, it shows strong intermolecular interactions ruling out the possibility of (0 0 1) being a slip plane. Moreover, face indexing analysis has previously reported that facet corresponding to (0 1 1) plane as morphologically the largest crystal facet with a relative surface contribution of 34.8% to the crystal habit of RIV [12]. This experimental evidence supports the presence of (0 1 1) as the primary slip plane. The *Eatt* of (1 0 2) plane was observed to be -83.3 kcal/mol. The presence of active slip plane in the crystal structure of RIV was further supported by the observed pop-ins in the nanoindentation (*p-h*) loading curve (Figure 8).
