Synthesis and metal coordination chemistry of (phenyl)(pyridin-2-ylmethyl) phosphinodithioic acid, [2-C ₅H ₄N]CH ₂P(S)(SH) (Ph)

A three-step synthesis for the bifunctional ligand (phenyl)(pyridin-2- ylmethyl)phosphinodithioic acid, [2-C ₅H ₄N]CH ₂P(S)(SH)(Ph) (3-H), was developed. The molecule was characterized by spectroscopic methods, and single crystal X-ray diffraction analysis, and the molecule found to exist in a zwitterionic form (3′). Protonation constants for 3′ were measured spectrophotometrically in 0.1 M NaClO ₄ aqueous solution. The coordination chemistry of 3′ toward CdCl ₂ and PtCl ₂ was explored, and the complexes [Cd(3′)Cl ₂] ₂ and [Pt(3 ^-) ₂]·CHCl ₃ were isolated and structurally characterized by single crystal X-ray diffraction methods. Complexation constants for 3′ with Cd(II), Zn(II) and La(III), as a function of pH, were measured by titration techniques. An initial effort to prepare the [pyridin-bis(2,6-yl-methylphosphinodithioic acid)] analog of 3-H led to the formation and isolation of (phenyl)(6- methylpyridin-2-ylmethyl)phosphinodithioic acid, [2-C ₅H ₃N(6-CH ₃)]CH ₂P(S)(SH)(Ph) (6-H), that was characterized by spectroscopic methods and single crystal X-ray diffraction analysis. As found with 3-H, 6-H, adopts a zwitterionic structural form (6′).