Et)]•2MeOH} of 3, labelled as 3c. The results of CASSCF calculations were also analysed with ab initio ligand field theory (AILFT), which resulted in energies of the f-orbitals of the ground state term ( 6 H15/2) spanning the energy intervals up to ~700 cm -1 as shown in Figure (left). The ligand field multiplets originating from the 6 H15/2 term formed upon applying the spin-orbit coupling, span the energy interval up to ~600 cm -1 (Figure (right)) and the respective energies are listed in Table . CASSCF calculated energy levels of Dy 3+ in complexes 1 -3 upto 25,000 cm -1 is given in Figure 72 , which reveals that the calculated energy for the excited state 4 F9/2 (±5 mj levels) is in the region 24190 -24560 cm -1 and hence energy transfer from the excited state of the ligands can easily take place via antenna effect on photoirradiation which thereby acts as the emitter level in the luminescence phenomenon. The large axial anisotropy of the respective KD states, gz >> gx, gy were found in all complexes 1 -3 (Table ). Interestingly, the easy axes roughly colinear and in 1 the magnetic easy axis of the ground state (KD1) is aligned in an antagonistic fashion to that of KD2 and KD3. Moreover, the transverse components of the g tensor of the KDs are smallest for 2 followed by 3 and 1. This indicates the presence of greater axiality in 2 followed by 3 and 1. Next, the magnetization reversal blocking barriers for 1 -3 are shown in Figure . The equivalent matrix elements of the transverse magnetic moment between the two lowest Kramers doublets (KDs) are small (less than 0.1 unit). This suggests that the temperature-assisted quantum tunnelling probability becomes relevant for the third KD, which has a value of around 170 cm -1 (244.6 K) for 1 -2, and in the case of 3, it varies between 170 (244.6 K) and 216 cm -1 (310.8 K) (Table ). These values are close to Orbach barriers determined from the analysis of AC susceptibility data. Finally, we can conclude that the inclusion of the second coordination sphere, where the two MeOH molecules are hydrogen-bonded to one acac ligand of 3, resulted in higher axiality of respective g-tensors, larger energy gaps (Table , compare 3b and 3c), and lower probabilities for the quantum tunnelling of the magnetization (Figure ). Herein, we performed an additional DFT calculation with PBE0 functional for 3b and 3c and the Mayer bond orders for Dy-O/N coordination bonds and Mulliken atomic charges for {DyN2O6} chromophore are listed in Table . The comparison of the Mayer bond orders and the Mulliken atomic charges shows that the formation of hydrogen bonds to O-donor atoms O12 and O13 of acac ligand resulted in larger atomic charges of these donor atoms, which is coupled to decrease the respective Dy-O bond orders. Thus, Dy-O12/O13 coordination bonds are more ionic in 3c. As a result, we can expect an increase of the orbital reduction factor  describing the covalency effect in the ligand field theory ( (3c) >  (3b)), which should lead to more efficient spin-orbit interaction (-(L)•S), and larger splitting of the energy levels.