Structures, metallophilic interactions and electronic excitation energy of linear metal chain complexes PdmPtn[PH2(CH2PH)m+n-2CH2PH2]3, a theoretical investigation

Abstract

The structures, metallophilic interactions and electronic excitation energy of linear metal chain complexes PdmPtn[PH2(CH2PH)m+n-2CH2PH2]3 (m + n = 2–5) (1–18) have been investigated by using MP2 and density functional theory (DFT) methods. Calculated results indicated that geometries of PdmPtn(PH2CH2PH2)3 (m + n = 2) (1–3) optimized by SVWN5 method are well consistent with those by MP2 method and experiment. Then, SVWN5 functional was used to the investigation of the large system of PdmPtn[PH2(CH2PH)m+n-2CH2PH2]3 complexes. The lowest energy structures of complexes 1–18 optimized by SVWN5 method are singlet. The lengths of Pd∙∙∙Pd and Pt∙∙∙Pt of Pdm[PH2(CH2PH)m-2CH2PH2]3 (m > 2) and Ptn[PH2(CH2PH)n-2CH2PH2]3 (n > 2) complexes at SVWN5 level are shorter than those of Pd2(PH2CH2PH2)3 and Pt2(PH2CH2PH2)3, indicating the interactions of Pd∙∙∙Pd and Pt∙∙∙Pt increase with the increase of the size of Pdm[PH2(CH2PH)m-2CH2PH2]3 and Ptn[PH2(CH2PH)n-2CH2PH2]3 complexes. Pd atoms in the mixed PdmPtn[PH2(CH2PH)m+n-2CH2PH2]3 complexes are favorable to locate at the ends of the metal chain. The lengths of Pd∙∙∙Pd and Pt∙∙∙Pt bonds in the mixed metal chain of PdmPtn[PH2(CH2PH)m+n-2CH2PH2]3 complexes have no significantly variation compared with those of the Pdm+n[PH2(CH2PH)m+n-2CH2PH2]3 and Ptm+n[PH2(CH2PH)m+n-2CH2PH2]3. But, the distances of Pd∙∙∙Pt of the mixed metal chain of PdmPtn[PH2(CH2PH)m+n-2CH2PH2]3 (m + n > 2) complexes are shorter than those of PdPt(PH2CH2PH2)3, showing the interaction between Pd and Pt increases as the increase of m + n. The WBIs of Pd∙∙∙Pd, Pd∙∙∙Pt and Pt∙∙∙Pt of complexes 1–18 are in the range of 0.22–0.25, 0.27–0.29 and 0.31–0.35, respectively, thus, there are weak interactions between adjacent transition metals in complexes 1–18. QTAIM analysis indicates that the interactions of Pd∙∙∙Pd, Pd∙∙∙Pt and Pt∙∙∙Pt of complexes 1–18 are not covalent, ionic or charge-shift bond. The gradient isosurfaces of complexes 1–18 show that the interaction between the adjacent transition metals is metallophilic interactions. The first electronic excitation energy of complexes 1–18 associated with HOMO → LUMO transition nonlinearly increases with m+n. In addition, the first electronic excitation energies of PdmPtn[PH2(CH2PH)m+n-2CH2PH2]3 complexes follow the order of Pdm+n[PH2(CH2PH)m+n-2CH2PH2]3 < PdmPtn[PH2(CH2PH)m+n-2CH2PH2]3 < Ptm+n[PH2(CH2PH) m+n-2CH2PH2]3.