Exploration of Solid-State vs Solution-State Structure in Contact Ion Pair Systems: Synthesis, Characterization, and Solution-State Dynamics of Zinc Diphenyl Phosphate, [Zn{O(2)P(OPh)(2)}(2)], Donor-Base-Supported Complexes

[Image: see text] A family of zinc phosphate complexes supported by nitrogen donor-base ligands have been synthesized, and their molecular structures were identified in both the solid (X-ray crystallography) and solution state (DOSY NMR spectroscopy). [Zn{O(2)P(OPh)(2)}(2)](∞) (1), formed from the reaction of Zn[N(SiMe(3))(2)](2) with HO(O)P(OPh)(2) coordinates to donor-base ligands, i.e., pyridine (Py), 4-methylpyridine (4-MePy), 2,2-bipyridine (bipy), tetramethylethylenediamine (TMEDA), pentamethyldiethylenetriamine (PMDETA), and 1,3,5-trimethyl-1,3,5-triazacyclohexane (Me(3)-TAC), to produce polymeric 1D structures, [(Py)(2)Zn{O(2)P(OPh)(2)}(2)](∞) (2) and [(4-MePy)(2)Zn{O(2)P(OPh)(2)}(2)](∞) (3), the bimetalic systems, [(Bipy)Zn{O(2)P(OPh)(2)}(2)](2) (4), [(TMEDA)Zn{O(2)P(OPh)(2)}(2)](2) (5), and [(Me(3)-TAC)Zn{O(2)P(OPh)(2)}(2)](2) (7), as well as a mono-nuclear zinc bis-diphenylphosphate complex, [(PMDETA)Zn{O(2)P(OPh)(2)}(2)] (6). (1)H NMR DOSY has been used to calculate averaged molecular weights of the species. Studies are consistent with the disassembly of polymeric 3 into the bimetallic species [(Me-Py)(2)·Zn(2){O(2)P(OPh)(2)}(4)], where the Me-Py ligand is in rapid exchange with free Me-Py in solution. Further (1)H DOSY NMR studies of 4 and 5 reveal that dissolution of the complex results in a monomer dimer equilibrium, i.e., [(Bipy)Zn{O(2)P(OPh)(2)}(2)](2) ⇆ 2[(Bipy)Zn{O(2)P(OPh)(2)}(2)] and [(TMEDA)Zn{O(2)P(OPh)(2)}(2)](2) ⇆ 2[(TMEDA)Zn{O(2)P(OPh)(2)}(2)], respectively, in which the equilibria lie toward formation of the monomer. As part of our studies, variable temperature (1)H DOSY experiments (223 to 313 K) were performed upon 5 in d(8)-tol, which allowed us to approximate the enthalpy [ΔH = −43.2 kJ mol(–1) (±3.79)], entropy [ΔS = 109 J mol(–1) K(–1) (±13.9)], and approximate Gibbs free energy [ΔG = 75.6 kJ mol(–1) (±5.62) at 293 K)] of monomer–dimer equilibria. While complex 6 is shown to maintain its monomeric solid-state structure, (1)H DOSY experiments of 7 at 298 K reveal two separate normalized diffusion coefficients consistent with the presence of the bimetallic species [(TAC)(2–x)Zn(2){O(2)P(OPh)(2)}(4)], (x = 1 or 0) and free TAC ligand.