**4. Conclusions**

A strong correlation between dimer/monomer equilibrium and catalysis was observed in the copper complexes synthesized in this work. These complexes were synthesized from Schiff bases from L-proline, exhibiting a square planar geometry. EPR analysis enabled us to verify the existence of a mixture of compounds in solution, especially in the methanol/water mixtures. We explored the hydrolytic capacity of these complexes in urea hydrolysis as a model reaction. As observed by EPR, in the acetonitrile/water mixture, the equilibrium shifted to a monomer and the hydrolysis of urea was too fast to detect the kinetics of ammonia formation by the Berthelot method. However, when the equilibrium monomer/dimer was present, as in the methanol/water mixture, the reaction proceeded slower and the ammonia formation kinetics could be detected in a saturation profile. This effect was shown to be due to the preferential solvation effect, by which hydrogen bonds formed between the secondary and tertiary coordination spheres stabilized the initial state of the aquation reaction. A strong influence of water concentration was observed in the methanol/water system, with special attention to CuIIL2 complex. A comparison with the dimeric perchlorate complex enabled us to visualize the importance of the monomer in the reaction, since the dimer produced ammonia from urea very slowly. In conclusion, this work relates a key feature of the chlorido bridges in a supramolecular structure of CuII complexes for an allosteric (upregulation) behavior in catalysis.

**SupplementaryMaterials:** The following are available online at http://www.mdpi.com/2624-8549/2/2/32/s1 [67–71], Figures S1–S17: NMR spectra of ligands, Figures S18–S22: HRMS of ligands, Figure S23: Optimized crystalline structure and number assignment of HL1, HL2, and HL3, Figures S24–S28: Comparison of FTIR between ligands and complexes, Figure S29: FTIR spectra of [CuIIL2(CH3OH)]ClO4 dispersed in KBr, Figures S30–S35: Comparison of UV–Vis between ligands and complexes, Figures S36–S53: EPR spectra of complexes, Figures S53–S55: Conductivity measurements of complexes in methanol/water, Figures S56–S62: HRMS of complexes, Figures S63–S68: Ammonia quantification produced by the complexes, Figure S69: Infrared spectra of reactions of the complexes (a) 30 s, (b) 600 s, and with (c) urea. Table S1: Crystal data and structure refinement of L1–L3, Table S2: Bond length for L1–L3, Table S3: Bond angles for L1–L3, Table S4: Comparison of the main infrared bands between ligands and complexes, Table S5: Comparison of transitions in the ultraviolet and visible region between ligands and complexes, Table S6: Comparison of oxidation and reduction potentials due to the cyclic voltammetry of ligands and complexes, Table S7: EPR parameters of aggregates and monomeric species of the CuII complexes of this work in dichloromethane at 77 K, Table S8: EPR parameters for the CuII complexes of this work in acetonitrile at 298 K, Table S9: EPR parameters for the CuII complexes of this work in acetonitrile/water (80/20) mixture at 298 K, Table S10: EPR parameters for the CuIIL2 and [CuIIL2(CH3OH)]ClO4 of this work in the methanol and methanol/water (80/20) mixture at 298 K, Table S11: Maximum amount of ammonia formed by the complexes of this work under the conditions of the acetonitrile/water and methanol/water mixture at 308 K. CCDC 1983221, 1983222 and 1983224 contain the supplementary crystallographic data for L1, L2, and L4, respectively.

**Author Contributions:** Conceptualization, C.B.C. and C.G.C.M.N.; Methodology, C.B.C.; Synthesis, C.B.C.; Characterization, C.B.C., O.R.N., and R.G.S.; Computer simulations, A.F.d.M. and F.M.C.; Formal analysis, C.B.C. and C.G.C.M.N.; Investigation, C.B.C. and C.G.C.M.N.; Resources, C.G.C.M.N., A.F.d.M., and O.R.N.; Data curation, C.B.C.; Writing—original draft preparation, C.B.C., and C.G.C.M.N.; Writing—review and editing, C.B.C. and C.G.C.M.N.; Supervision, C.G.C.M.N.; Project administration, C.G.C.M.N.; Funding acquisition, C.G.C.M.N. and A.F.d.M. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by FAPESP (projects 2012/15147-4, 2013/07296-2 and 2016/01622-3), CNPq for a master fellowship (132842/2017-3), and CAPES (project 001). Otaciro Rangel Nascimento thanks CNPq (project 305668/2014-5). A.F.d.M. thanks CNPq for a Research Fellowship.

**Acknowledgments:** We would also like to thank Diego E. Sastre for editing the images and Elton Sitta for the aid in the in situ FTIR experiments. The authors acknowledge the National Laboratory for Scientific Computing (LNCC/MCTI, Brazil) and UFSCar for providing the high-performance computing resources of the SDumont supercomputer (http://sdumont.lncc.br) and of the Could@UFSCar, respectively, both of which have contributed to the results reported in this paper.

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