All structures were optimized in gas phase with the scalar-relativistic ZORA Hamiltonian, the B3LYP* exchange-correlation functional, Grimme's D3 37 dispersion corrections, and all-electron ZORA Slater-type TZ2P basis sets, all as implemented in the ADF program system. The tightest practicable criteria were used for both SCF and geometry cycles as well as for frequency analyses; the latter established the optimized structures as true minima. NBO analyses were performed based on single-point OLYP