###### Abstract  
The title compound tetraphenylborate salt of _domidine_ (Catapres(r)), 2-(2,6-dichlorophenylamino)-2-imidazoline tetraphenylborate (**3**), was prepared in 76 % yield by the reaction of 2-(2,6-dichlorophenylamino)-2-imidazoline hydrochloride ( clonidine hydrochloride) (**1**) with sodium tetraphenylborate (**2**) in deionized water through anion exchange reaction at ambient temperature. The structure of the title borate salt was characterized by UV, thermal analysis, mass and NMR analyses. White crystals of (**3**) suitable for an X-ray structural analysis were obtained by slow growing from acetonitrile. The molecular structure of the titled compound (**3**) was crystallized in the acetonitrile, \(P_{21}/c\), \(a\) = 9.151 (3) A, \(b\) = 12.522 (3) A, \(c\) = 25.493 (6) A, \(\beta\) = 105.161 (13)\({}^{\circ}\)\(V\) = 2819.5 (13) A\({}^{3}\), \(Z\) = 4. A DFT quantum chemistry calculation method was employed to investigate the interaction mechanism of clonidine with tetraphenylborate. The stable configurations of the complexes of clonidine with tetraphenylborate with electrostatic interactions were obtained. Finally, the interaction strength and type of the complexes were studied through the reduced density gradient (RDG) function. This study provides new theoretical insight into the interaction mechanism and a guide for screening and designing the optimal clonidine and tetraphenylborate reacting to form the complex.  
clonidine; Catapres(r); anion exchange; tetraphenylborate salt; crystal structure; X-ray analysis 2022 2022 28 March 2022  
sensor [4] was used for the determination of clonidine in some pharmaceutical formulations. The suggested sensor shows a dynamic range with a Nernstian response of 58.3 mV/decade, detection limit of 6.5 \(\times\) 10\({}^{-6}\) M, fast response time and good life time of about one and half month.  
Another application of clonidine-tetraphenyl borate was used as sensing material in the PVC membrane sensor for the potentiometric determination of amitriptyline [5] at nanomolecular concentration. The proposed sensors showed a calibration range from 10 nM to 1.0 mM amitriptyline. The detection limit was 5.0 nM and the Nernstian response was 58.4 mV/decade. Sodium tetraphenyl borate as an ion-pair reagent was reported for constructing PVC membrane sensors for many drugs [6; 7; 8; 9].  
A DFT quantum chemistry calculation method was employed to investigate the interaction mechanism of clonidine with tetraphenylborate. The interaction strength and type of the complex were studied through the reduced density gradient function. This study provides new theoretical insight into the interaction mechanism, a guide for screening and designing the optimal clonidine and tetraphenylborate reacting to form the complex.  
Here, we report the synthesis and characterization of the reaction of clonidine with tetraphenyl borate for the development of a new ion-pair complex. Characterization of the ion-pair complex was performed using differential scanning calorimetry, thermal gravimetric analysis, UV spectrometry, mass spectrometry, H NMR and X-structure. Furthermore, the electronic structure was examined by TD-DFT to investigate the interaction mechanism of clonidine with tetraphenylborate complex.