Source data for calculations performed with Gaussian 16 (file: ONIOM_Model_FIN.out) and Orca 5.0.3 (files: DFT_Model_Step1-37_FIN.out, DFT_Model_Step38-52_FIN.out, CASSCF_Model_statespec-T1_FIN.out, CASSCF_Model_statespec-T0_FIN.out, CASSCF_Model_stateavg_FIN.out). For the DFT based geometry optimization of the smaller model used the calculations had to be restarted after step 37 due to run time restrictions (see files: DFT_Model_Step1-37_FIN.out and DFT_Model_Step38-52_FIN.out) .