Theoretical Studies on the Fe-M Interactions and 31P NMR in Fe(CO)3(EtPhPpy)2MX2 (X=NCS, SCN, Cl; M=Zn, Cd, Hg)

To study the Fe-M interactions and their effects on P-31 NMR, the structures of Fe(CO)(3)(EtPhPpy)(2) 1, Fe(CO)(3)(EtPhPpy)(2)M(NCS)(2) (2: M=Zn, 3: M=Cd, 4: M=Hg) and Fe(CO)(3)(EtPhPpy)(2)CdX2 (5: X=Cl, 6: X=SCN) were investigated by density functional theory (DFT) PBE0 method. The stabilities S of complexes follow S(2)>S(3)>S(4) and S(3), S(6)>S(5), indicating that 6 is stable and may be synthesized. The complexes with thiocyanate are more stable than that with chloride in Fe(CO)(3)(EtPhPpy)(2)CdX2. The strength I of Fe-M interactions follows I(2)approximate to I(3)<I(4). The Fe-Cd interactions of 3 and 6, which contain thiocyanate, are stronger than that of 5 with chloride. The charge-transfer, which enhances with the increasing of Fe-M interaction strength, comes from Et, Ph, py, CO groups towards P, Fe, and M atoms. Because the delocalization of thiocyanate disperses the charge of M2+, the charge-transfer of the complexes with thiocyanate is stronger than that with chloride. There is a or-bond between Fe and Hg atoms in 4. However, in binuclear complexes except 4, the Fe-M interactions act as n(Fe)-> n(M), sigma(P-Fe)-> n(M) and sigma(C-Fe)-> n(M) delocalization, and the N-M interactions mainly act as n(N)-> n(M) delocalization. In binuclear complexes, due to the Fe -> M interactions, the strong sigma(Fe-C)->*(Fe-P) or sigma(Fe-Hg)->sigma*(Fe-P) delocalization and the charge-transfer, the electron density on P nucleus is increased, and thus upfield P-31 chemical shifts are caused (compared with mononuclear complex 1).