3d‐metal (Cr to Zn) Nitrilotris(Methylenephosphonate)s with different coordination symmetries: Electronic Structure and Chemical Bond

In this study, we present a comparative study of two parallel isostructural series of the 3d‐metal coordination complexes with nitrilotris(methylenephosphonic acid) H6{N(CH2PO3)3} (NTP, H6L) as a ligand. The series were analyzed by comparing their complexes in the spatial distribution of electron density and electron‐energy spectrum extracted from the XRD and XPS data, respectively. The first isostructural series (M=CrII, MnII, FeII, CoII, NiII, CuII, ZnII) contains a fourfold (four‐times) protonated ligand (H4L2−) and has a slightly distorted octahedral coordination of 3d‐metal atom by three O atoms of PO3 groups and three water molecules. The second isostructural series (M=MnII, CoII, CuII, ZnII) with the fully deprotonated ligand (L6−) has a distorted trigonal‐bipyramidal coordination of 3d‐metal atom with four O atoms of PO3 groups and N atom in the vertex. The complex of L6− with NiII, which is structurally close to the second series complexes, has a slightly distorted octahedral coordination of Ni atom with four O atoms of PO3 groups, N atom and an additional water molecule. For fully deprotonated PO3 groups, considerable shift of electron density is observed away from the center of the phosphorus atom to all the three P−O bonds. The protonation of only one of the oxygen atoms causes the shift of electron density from all the three P−O bonds to the center of the phosphorus atom and localization of P3s electron pair.