All atoms were described by the ANO-RCC basis set , with the contraction [8s7p5d3f2g1h] for Ln atoms, [4s3p2d1f] for C, N, O atoms coordinating the metal, [3s2p] for C, N, O atoms not coordinating the metal, [2s] for H. Scalar relativistic terms were included in the one-electron part of the electrostatic Hamiltonian in all the HF, CAHF, and CASCI-SO computations, within the second order Douglas-Kroll-Hess (DKH2) approximation . In CASCI-SO evaluations, the spinorbit interaction were included by the atomic approximation to the Breit-Pauli Hamiltonian, in which the two-electron spin-orbit integrals involving the atomic basis functions on multiple centers are discharged. The Cholesky representation of the electron repulsion integrals was used to speed up the calculations, with d = 10 8 44 .