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

Abstract

Hydrous crystals of [{PdII(bpy)}2(μ-x-tart)]·nH2O (bpy: 2,2′-bipyridine; tartH2 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 [{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.

Can Stacking Interactions Exist Beyond the Commonly Accepted Limits?

“…Stacking or π···π interactions are among the most common (together with hydrogen and halogen bonds) noncovalent interactions found in both natural and synthetic systems . These interactions play a very important role in controlling of the crystal packing − and recognition of aromatic compounds (as the auxiliary stabilizing force), − in regulation of stereoselectivity in synthetic organic reactions, they are significant in biological systems (for example in nucleic acids – DNA and RNA), and also govern the processes important in many areas of science, such as analytical chemistry, medical chemistry, , and nanotechnology. , Thus, the studies on their role in both model and real systems evolved drastically during past decades.…”

Chromism of Tartrate-Bridged Clamshell-like Platinum(II) Complex: Intramolecular Pt–Pt Interaction-Induced Luminescence Vapochromism and Intermolecular Interactions-Triggered Thermochromism

“…The resonances for the aromatic bpy protons and aliphatic Me protons split to be six peaks and two peaks, respectively (Figure a). The characteristic signal pattern originates from not only trans influence of the two oxygen atoms, coordinated to each metal center, but also a shielding effect between the intramolecular 4 Me 2 bpy moieties, suggesting the presence of π–π interaction. , …”

“…The characteristic signal pattern originates from not only trans influence of the two oxygen atoms, coordinated to each metal center, but also a shielding effect between the intramolecular 4 Me 2 bpy moieties, suggesting the presence of π−π interaction. 5,11 The UV−vis absorption spectrum in DMF at room temperature showed an intense absorption band at 275 nm, assigned to a ligand-centered π−π* transition inside bpy (LC, L = bpy), and a relatively weak broad band at 488 nm, derived from mixed transitions of metal-to-ligand charge transfer (MLCT) and interligand charge transfer (L′LCT, L′ = tart), 12 as shown in Figure 2b. The complex was non-emissive in fluid DMF solution at room temperature but emissive in rigid DMF glass at 77 K, when excited at 365 nm.…”

A homochiral tartrate-bridged dinuclear chromium(iii) complex anion with a resonance-assisted hydrogen bond for proton conduction

“…In most of the struc-tures found in the Cambridge Structural Database (CSD), 20 the L-tartrate ligand bridges the transition metal centres, leading either to extended polymeric structures, as in a series of isomorphous compounds {[M(NN)(L-tart-H 2 )]•xH 2 O} n (M 2+ = Mn, Co, Cu, and Zn; NN = 2,2′-bipyridine, 1,10-phenanthroline; L-tart-H 2 = dianion of L-tartaric acid; x = 5, 6), [21][22][23][24][25][26] or to isolated dinuclear complexes of the formula [{M(NN)} 2 (L-tart-H 2 )] (M 2+ = Pd and Pt). 27,28 Complexes containing two tartrate bridging groups of the same enantiomeric configuration are considered to be energetically more stable than those with bridges of opposite chirality. 19 For this reason, these complexes are also very stable toward intramolecular racemization, making them suitable building blocks for the construction of chiral extended inorganic-organic frameworks with a polar crystal structure.…”

“…In contrast to divalent transition metal cations, [21][22][23][24][25][26][27][28] chromium(III) ions form bridged dinuclear complexes with meso-, D-and L-tartaric acid, in which one proton per two tetranegative tartrate ligands remains undissociated (as shown in Scheme 1). 19,29 The structure of the mesotartrate-chromium(III) complex anion with an aromatic N-donor ligand was described by Ortega et al 30 and the structure of the L-tartrate-chromium(III) complex anion is topologically the same.…”