Inverted sandwich type dinuclear chromium(I) complex and its analogues of scandium(I), titanium(I), vanadium(I), manganese(I), and iron(I): theoretical study of electronic structure and bonding nature.

Inverted sandwich type chromium(I) complexes, (mu-eta(6):eta(6)-C(6)H(5)CH(3))[Cr(DDP)](2) (DDPH = 2-(4-{(2,6-diisopropylphenyl)imino}pent-2-ene) and (mu-eta(6):eta(6)-C(6)H(5)CH(3))[V(DDP)](2), synthesized by Tsai et al., and (mu-eta(6):eta(6)-C(6)H(6))[Cr(DDP)](2) synthesized by Monillas et al., were theoretically investigated with MRMP2 and DFT methods, where model compounds (mu-eta(6):eta(6)-C(6)H(6))[Cr(AIP)](2) (AIPH = (Z)-1-amino-3-imino-prop-1-ene) were mainly employed. Both computational methods succeeded in reproducing the experimental facts that the chromium and vanadium complexes take surprisingly high spin states, septet and quintet spin states, respectively. MO diagrams of these complexes present a clear understanding of the reasons why they take such high spin states. We also calculated their analogues, (mu-eta(6):eta(6)-C(6)H(6))[M(DDP)](2) (M = Sc, Ti, Mn, or Fe). The spin multiplicities of the Sc and Ti complexes were calculated to be singlet and triplet, respectively, by the DFT(B3LYP) method. Those of Mn and Fe complexes were calculated to be quintet and triplet, respectively, by the DFT(B3LYP) method, but nonet and singlet, respectively, by the MRMP2 method, suggesting that the DFT method cannot be applied to these complexes. The MRMP2 calculations indicate that the spin multiplicity increases upon going to Mn from Sc and reaches the maximum, nonet spin state, at Mn, and then suddenly decreases to singlet at Fe. This interesting change in spin multiplicity is discussed in terms of occupation of MOs.