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.