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.

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 [Δ H = -43.2 kJ mol -1 (±3.79)], entropy [Δ S = 109 J mol -1 K -1 (±13.9)], and approximate Gibbs free energy [Δ G = 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.