## 3 Results and Discussion
### Computational Study
#### 3.3.3 Non-Covalent Interaction (NCI) Index  
On the basis of the RDG, the NCI between clonidine and tetraphenylborate was graphically established. NCI-RDG analysis can provide information on weak NCI in real space and depict different regions where NCI appear. Thus, using simple color codes,  
\begin{table}
\begin{tabular}{l l l l} \hline Cl1—C5 & 1.734 (4) & N3—C3 & 1.333 (5) \\ \hline Cl2—C9 & 1.724 (4) & N3—C4 & 1.416 (5) \\ \hline N1—C1 & 1.47  
the approach can differentiate hydrogen bonding, van der Waals, and repulsive steric interactions [25; 26].  
High repulsion is indicated by red regions, strong attraction is indicated by blue regions, and electrostatic interactions are indicated by green regions. The sign of \(\lambda_{2}\) (the  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Bond Distance** & **Exp.** & **DFT-B3 LYP** & **Bond Distance** & **Exp.** & **DFT-B3 LYP** \\ \hline Cl1—C5 & 1.734 (4) & 1.756 & N3—C3 & 1.333 (5) & 1.337 \\ \hline Cl2—C9 & 1.724 (4) & 1.739 & N3—C4 & 1.416 (5) & 1.419 \\ \hline N1—C1 & 1.475 (5) & 1.473 & C10—B1 & 1.653 (5) & 1.662 \\ \hline N1—C3 & 1.311 (6) & 1.326 & C16—B1 & 1.661 (6) & 1.655 \\ \hline N2—C3 & 1.328 (5) & 1.345 & C22—B1 & 1.647 (6) & 1.653 \\ \hline N2—C2 & 1.467 (6) & 1.474 & C28—B1 & 1.655 (7) & 1.666 \\ \hline \multicolumn{5}{c}{**Bond angle**} \\ \hline C1—N1—C3 & 110.3 (3) & 110.539 & N1—C3—N2 & 111.5 (4) & 111.402 \\ \hline C2—N2—C3 & 109.1 (4) & 109.892 & N1—C3—N3 & 125.9 (4) & 123.444 \\ \hline C3—N3—C4 & 123.6 (4) & 125.239 & N3—C4—C5 & 121.2 (4) & 121.628 \\ \hline C15—C10—B1 & 123.8 (3) & 121.836 & N3—C4—C9 & 120.9 (4) & 120.495 \\ \hline C11—C10—B1 & 122.3 (3) & 123.0899 & Cl1—C5—C6 & 119.2 (3) & 119.213 \\ \hline C17—C16—B1 & 122.0 (3) & 119.0318 & Cl1—C5—C4 & 119.8 (3) & 119.851 \\ \hline C21—C16—B1 & 122.7 (3) & 125.277 & Cl2—C9—C8 & 119.3 (3) & 118.237 \\ \hline C23—C22—B1 & 120.6 (3) & 119.147 & Cl2—C9—C4 & 119.5 (3) & 120.234 \\ \hline C27—C22—B1 & 123.9 (3) & 125.431 & C16—B1—C28 & 109.7 (3) & 105.195 \\ \hline C33—C28—B1 & 123.3 (4) & 120.389 & C22—B1—C28 & 107.2 (3) & 105.913 \\ \hline C29—C28—B1 & 122.9 (3) & 124.664 & C16—B1—C22 & 109.8 (3) & 111.056 \\ \hline N1—C1—C2 & 101.2 (3) & 101.827 & C10—B1—C16 & 107.6 (3) & 110.477 \\ \hline N2—C2—C1 & 102.1 (3) & 101.843 & C10—B1—C22 & 108.4 (3) & 111.494 \\ \hline N2—C3—N3 & 122.6 (4) & 125.153 & C10—B1—C28 & 114.0 (4) & 112.802 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Geometric parameters for the clonidine–tetraphenylborate complex obtained using DFT techniques and B3 LYP functionals. Distances are measured in Å, and bond angles are measured in degrees.  
Figure 6: (**a**) Non-covalent interaction (NCI) scatter diagram and (**b**) reduced density gradient (RDG) analysis of the clonidine–tetraphenylborate complex.  
second largest eigenvalue of the Hessian electron density matrix) merges to create sign(\(\lambda_{2}\))\(\rho\). Hydrogen bond interactions are distinguished from other interactions using the RDG function and sign(\(\lambda_{2}\))\(\rho\). The values of sign(\(\lambda_{2}\))\(\rho\) range from \(-\)0.05 to 0.05 a.u., as illustrated in Figure 6a; \(-\)0.015 a.u. is the highest negative value in green, while 0.011 a.u. is the least positive value in reddish green, both of which are represented by the spikes on the left. The clonidine-tetraphenylborate complex's stability may be due to van der Waals and steric interactions [27].  
The green and red regions of the RDG isosurface map (Figure 6a,b) suggest the presence of van der Waals and steric effects, respectively, inside the clonidine-tetraphenylborate complex. As demonstrated in Figure 6, the van der Waals and steric interactions are responsible for molecule binding, which is more favorable to system stabilization. This result agrees with the AIM analysis described in Section 2.4.