Unexpected Self-Assembly Pathway to a Pd(II) Coordination Square-Based Pyramid and Its Preferential Formation beyond the Boltzmann Distribution.

Experimental and theoretical investigations of the self-assembly process of a Pd(II) coordination M6L4 square-based pyramid (SP) were conducted. It was found that the probable self-assembly pathway, in which the dimerization of M2L2 with two M leads to SP, expected from the connectivity of the building blocks is not a major self-assembly pathway to the M6L4 SP. Whether the M6L4 SP is assembled or M2L2 is trapped is determined by an inter- or intramolecular reaction in a chain-like M2L2X, where X is a leaving ligand. The kinetically trapped state where the M6L4 SP is produced from M2L2 beyond the Boltzmann distribution was realized by a concentration-induced process and was kept for at least 2 months at 298 K.