Stereochemistry of Pb(II) Complexes with Aminopolycarboxylic Ligands. The Role of a Lone Electron Pair

Abstract

The structures of complex anions of Pb(II) coordination compounds (complexonates) with monoamino-, diamino-, and polyaminopolycarboxylic acids as ligands were interpreted in terms of a model of the valence shell electron pair repulsion. A lone electron pair ( E ) in all structurally studied Pb(II) complexonates with carboxyl-containing complexones was shown to be stereochemically active, and the structure of Pb coordination polyhedron was found to depend on both the ligand dentate number and on its degree of protonation. As the ligand dentate number increased, the coordination number (C.N.) of a central atom changed from 4 + E for monoamine complexonates to 6 + E for diamine and triamine complexonates. With allowance for secondary bonds in the structure, the C.N. of the Pb atom increased to 7-9. The Pb(II) complexonates with nitrilotriacetic acid exhibit the formation of a new type of coordination polyhedron for post-transition elements in a low-valent state with five electron pairs in a valence shell (including one lone electron pair), i.e., the ψ -trigonal bipyramid with E in the axial position.

High-temperature monoclinic α-SrHfF6, and isostructural α-SrZrF6: associating Hf2F12bipolyhedra and SrF8snub disphenoids

“…Two bipyramids are connected through F2-F2 i edges [symmetry code: (i) Àx + 2, Ày, Àz + 2], forming an Hf 2 F 12 bipolyhedron ( Fig. 1), which has been described frequently in fluoridozirconate and fluoridohafnate structures (Davidovich, 1998). Because of this research papers…”

Synthesis and Complex Study of the Crystal Hydrate Zn2ZrF8·12H2O

“…The stereochemistry of complex zirconium fluorides is characterized by high coordination numbers of the central atom (6, 7, and 8) and versatile in configuration coordination polyhedra. The most complete analysis of stereochemistry of complex zirconium fluoride compounds was presented in the literature 1,2. Eight‐coordinated zirconium anions are known to be present most often in crystal structures, but, as a rule, they form polymers with the stoichiometric F/Zr ratio smaller than 8.…”

The Chelating Behaviour of 3‐(4‐X‐Phenyl)‐2‐sulfanylpropenoic Acids with the PbII Ion – Relevance of the Lone Electron Pair in the Supramolecular Structures of the 2:1 Complexes

“…For example, fully or partially deprotonated ethylenediaminetetraacetic acid (H 4 EDTA) chelates the metal ion through the two aminic N atoms and four carboxylic O atoms, one from each carboxylate group. [7] In [Pb(PEN)] (PEN = d-penicillaminato), the ligand is N,O,S tridentate in the solid state. [8] In turn, the meso-2,3-dimercaptosuccinato ligand (m-DMSA 4-) binds Pb II ions through one O atom and two S atoms in aqueous solution.…”