Coupled cluster: All CCSD(T) calculations with the aug-cc-pVQZ and aug-cc-pV(Q+d)Z 16 basis set were carried out with CFOUR (version 2.0/2.1), analytical gradients and Hessians, in parallel where needed, using unrestricted Hartree-Fock for open-shell systems. Note that a bugfix (Dec. 2021, see SI) was needed for being able to run in parallel with unrestricted coupled cluster protocols. Basis sets not available in standard CFOUR (e.g. def2-TZVPD or aug-cc-pV(Q+d)Z) were obtained from the basis set exchange. The frozen core approach was used within the solving of the coupled cluster equations. The geometry optimization typically had SCF and coupledcluster convergence criteria of 1.0•10 -10 , geometry converge of 1.0•10 -8 atomic units, leading to electronic energies accurate to at least 1.0•10 -8 Hartree. The two-electron integrals were in all cases treated with the AOBASIS formalism to reduce disk space, in conjunction with the ECC program (with conventional UCCSD(T) for complex 2).