3 d ‐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 3 d ‐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 2− ) 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 6− ) has a distorted trigonal‐bipyramidal coordination of 3 d ‐metal atom with four O atoms of PO 3 groups and N atom in the vertex. The complex of L 6− 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 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 P3 s electron pair.