*2.6. Computer Simulations*

Geometries for the CuIIL1 monomer and the dimer were optimized at the semi-empirical GFN1-xTB level in vacuum using the xtb software [37–39], with convergence criteria for the self-consistent charge (SCC) iterations of 2·10−<sup>7</sup> Ehfor the energy change and 4·10−<sup>6</sup> for the charge change between cycles and for the geometry optimization of 1·10−<sup>6</sup> Eh for the energy change between steps and a maximum gradient of 8·10−<sup>4</sup> Eh/<sup>α</sup>. All calculations were performed with an electronic temperature of 500 K to allow some degree of Fermi smearing of nearly-degenerate energy levels and to take static correlation into account. All model systems were considered neutral with each Cu(II) cation in the Ar[3d9] configuration, yielding a doublet state for the monomer. Regarding the dimer, both singlet and triplet states were considered for the sake of completeness. The same protocols were applied to acetonitrile, water, and methanol molecules in vacuum. After full geometry optimization of the monomer and the two spin states of the dimer, further geometric relaxation was performed by means of 10 ps-long molecular dynamics simulations performed in the canonical, constant-NVT ensemble (meaning amount of substance (N), volume (V) and temperature (T) are conserved), using the Berendsen weak-coupling scheme to control the temperature around 300 K. Equations of motion were integrated using a 0.5 fs time step, and recording structures and energies each of 0.5 ps. The last structure for each system was subjected to further geometry optimization and these optimized structures were considered as the lowest lying reference states for the thermochemical analyses. The next step of the modeling consisted of searching the thermodynamically most probable position and relative orientation of each solvent around each complex, as described in detail in the Supplementary Materials. This systematic search amounted toca. 1 million quantum chemical calculations and the most probable solvent-CuIIL1 structures were subjected to further geometry optimization as described above.
