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

Abstract

In this study, we present a comparative study of two parallel isostructural series of the 3d-metal coordination complexes with nitrilotris(methylenephosphonic acid) H 6 {N(CH 2 PO 3) 3 } (NTP, H 6 L) 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=Cr II , Mn II , Fe II , Co II , Ni II , Cu II , Zn II) contains a fourfold (four-times) protonated ligand (H 4 L 2À) and has a slightly distorted octahedral coordination of 3d-metal atom by three O atoms of PO 3 groups and three water molecules. The second isostructural series (M=Mn II , Co II , Cu II , Zn II) with the fully deprotonated ligand (L 6À) has a distorted trigonal-bipyramidal coordination of 3d-metal atom with four O atoms of PO 3 groups and N atom in the vertex. The complex of L 6À with Ni II , which is structurally close to the second series complexes, has a slightly distorted octahedral coordination of Ni atom with four O atoms of PO 3 groups, N atom and an additional water molecule. For fully deprotonated PO 3 groups, considerable shift of electron density is observed away from the center of the phosphorus atom to all the three PÀ O bonds. The protonation of only one of the oxygen atoms causes the shift of electron density from all the three PÀ O bonds to the center of the phosphorus atom and localization of P3s electron pair.