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

Hydrous
crystals of [{PdII(bpy)}2(μ-x-tart)]·nH2O (bpy: 2,2′-bipyridine; tartH22–: 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 [{PdII(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.