Metal-Induced Isomerization of a Molecular Strand Containing Contradictory Dynamic Coordination Sites

A new hydroxymethyl terminated pyrimidine-hydrazone (pym-hyz) ligand (L1) was synthesized with a central hyz-pyridine-hyz (hyz-py-hyz) motif replacing the usual hyz-pym-hyz unit, to create a molecular strand that underwent metal-induced isomerization with a minimal net change in ligand length. NMR spectroscopy showed that L1 had a horseshoe shape due to the hyz-py-hyz and pym-hyz bonds adopting transoid conformations. The ligand was successfully reacted with Pb­(II), Zn­(II), and Ag­(I) salts in either CH3CN or CH3NO2 resulting in horseshoe-shaped Mn+3L1A3n (where A = ClO4– or SO3CF3–) complexes in the solution phase. Crystals were grown from these solutions, the structures of which were highly dependent on the metal ion and solvent used, and were distinctly different from those seen in solution. The crystals grown from mixtures of Pb­(ClO4)2·3H2O and L1 in either CH3CN or CH3NO2 resulted in the horseshoe-shaped [Pb3L1(ClO4)4(H2O)2]­(ClO4)2­·CH3CN (1) complex or the {[Pb3L1(ClO4)4­(H2O)]­(ClO4)2}∞­·CH3NO2 (2) helical coordination polymer, respectively. The horseshoe-shaped [Pb3L1(SO3CF3)6]­·CH3CN (3) complex was crystallized from a solution of Pb­(SO3CF3)2­·H2O and L1 in CH3CN, while the crystals grown from the solution of Zn­(SO3CF3)2 and L1 in CH3CN consisted of the zigzag-shaped [Zn3L1(H2O)7]­(SO3CF3)6 (4) complex. The [Ag3(L1)2]­(SO3CF3)3 (5) double-helicate and the macrocycle-like [Ag6(L1)2]­(SO3CF3)6 (6) complex were crystallized from solutions of AgSO3CF3 and L1 in either CH3CN or CH3NO2, respectively.