Lattice Water-Induced Helical Stacking of Tartrate-Bridged Dinuclear Palladium(II) Complexes: The Role of Hydrogen Bonding

Hydrous crystals of [{Pd II (bpy)} 2 (μ-x-tart)]· n H 2 O (bpy: 2,2′-bipyridine; tartH 2 2–: tartrate; 1a: x = l, n = 6; 2a: x = d, n = 6; 3a: x = dl, n = 4; 4a: x = meso, n = 4) and anhydrous crystals of [{Pd II (bpy)} 2 (μ- l -tart)] ( 1b ) were isolated from aqueous and MeOH solutions, respectively. X-ray crystallography revealed the stacked structures of clamshell-like dinuclear units in 1a – 3a and 1b, where intramolecular metal–metal and π–π stacking interactions were observed. Right- and left-handed helically stacked columns were formed in the 1a and 2a crystals, respectively. The significant role of hydrogen bonding among lattice water molecules and tartrate is suggested because 1b exhibited a zigzag arrangement only through intermolecular metal–metal interactions. In 3a, l - and d -tart units stacked alternately in a zigzag arrangement with intermolecular π–π interactions. In 4a, dimeric aggregates of the twisted dinuclear units further formed a 2D sheet architecture.