Typical FeII spin crossover (SCO) complexes exhibit {N6} coordination which offers a stronger ligand field than the {N4S2} ligand set. Recently in [1] the synthesis, crystal structures, magnetic and spectroscopic studies on the family of neutral mononuclear complexes, [Fe(bpte)(NCE)2] (where E=S, Se, or BH3) with mixed nitrogen-sulfur ligand surrounding of the FeII ions have been reported. A priori it is not clear what is the origin of SCO in these complexes which contain in the nearest surrounding of the FeII ion four nitrogen ligands creating a crystal field of intermediate strength and two sulfur ones giving a much weaker field. The aim of the present communication is to give an explanation of the SCO phenomena in iron(II) complexes with N4S2 coordination environment [1].  Since of the weaker crystal field acting on the iron(II) ion in the [Fe(bpte)(NCE)2] complexes it has been assumed that besides the iron(II) states with the spin values in the spin conversion the states with also participate. The calculations of the energies of the complex for the states of the FeII ion with spin values 0, 1 and 2 have been performed within the frames of the density functional theory (DFT) using the program package ORCA 4.012 [2]. In the work the B3LYP functional [3] together with Grimme´s dispersion correction have been employed. The def2-TZVP [4] basis together with the auxiliary SARC/J and def2-TZVP/C basis sets [5] have been used. Calculations labeled RIJCOSX [6] used the COSX approximation for the exchange terms in conjunction with the RI-J approximation. For the COSX approximation the numerical accuracy has been set by the Gridx5 and FinalGrid6 keywords. To control the target precision of the energies and the wave functions for all clusters the ORCA keyword ―VeryTightSCF‖ (SCF stands for the self-consistent field) was used, as a result the ground state energies were converged to 10-9 hartree. The performed calculations demonstrated that the complex [Fe(bpte)(NCS)2] is in the state with the spin value S=2 at temperatures T=90 and 230 K. This complex does not demonstrate the change of the ground state spin i.e. spin crossover. At temperature 90K the α-polymorph of the [Fe(bpte)(NCSe)2] complex is in the low-spin state with S=0, at the intermediate temperature 120K the spin of the ground state of this complex acquires the value S=1 and at room temperature the complex is in the high- spin state corresponding to S=2, thus in this case the state with the intermediate spin value S=1 participates in the spin transformation. The same situation unusual for spin crossover compounds takes place for the γ-polymorph of the [Fe(bpte)(NCSe)2]complex. Meanwhile, for the iron(II) complex with E=BH3 the ground states correspond to the spins S=0 and 2 at temperatures 150 K and 295 K, respectively. In this case the classical picture of spin crossover takes place.