Tuning Molecular Structures Using Weak Noncovalent Interactions: Theoretical Study and Structure of trans-Bis(2-chloropyridine)dihalocopper(II) and trans-Bis(3-chloropyridine)dibromocopp

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• 作者：Firas Awwadi ; Roger D. Willett ; Brendan Twamley
• 刊名：Crystal Growth & Design
• 出版年：2011
• 出版时间：December 7, 2011
• 年：2011
• 卷：11
• 期：12
• 页码：5316-5323
• 全文大小：959K
• 年卷期：v.11,no.12(December 7, 2011)
• ISSN：1528-7505

文摘

The effect of the weak noncovalent interactions (C鈥揌路路路X鈥揅u, C鈥揧路路路Cu, and C鈥揧路路路H鈥揅) on the molecular structure of Cu(nYP)₂X₂ (where nYP denotes the n-halopyridine ligand, n = 2 or 3, X = Cl^{鈥?/sup> or Br鈥?/sup>, and Y = H, F, Cl, or Br) has been investigated using the DFT/B3LYP method. The molecular structure of Cu(nYP)₂X₂ was optimized using two different starting geometries; the two Y groups are (a) L-cis arrangement and (b) L-trans arrangement with respect to each other, L for ligand. The optimized molecular structures of the Cu(nYP)₂X₂ structures indicate that the L-cis isomer is more stable than corresponding L-trans one by avg = 9.45 kJ/mol (range 4.29鈥?3.15 kJ/mol). The analysis of theoretical results indicates the strength of the noncovalent interactions follows the order C鈥揧路路路H鈥揅 < C鈥揧路路路Cu < C鈥揌路路路X鈥揅u. The L-cis isomer is stabilized by C鈥揌路路路X鈥揅u interactions, in contrast, the L-trans isomer is stabilized by C鈥揧路路路H鈥揅 and C鈥揧路路路Cu. There is no perfect agreement (L-trans and L-cis-isomerism) between the optimized structures and the solid-state molecular structures. This is possibly because the optimization process ignores the effect of intermolecular interactions, and the energy difference between each L-trans and L-cis corresponding isomer is quite small. The structures of Cu(2CP)₂X₂ and Cu(3CP)₂Br₂ have been determined. An infinite [Cu(3CP)₂Br₂]n chain structure forms based on the Cu路路路Br semicoordinate bond, whereas the semicoordinate bond connects the molecular species of Cu(2CP)₂X₂ to form a dimer structure. The chains of Cu(3CP)₂Br₂ are subsequently linked via C鈥揅l路路路Br鈥揅u halogen bonding interactions besides the weak C鈥揌路路路X鈥揅u hydrogen bonding interactions in the three-dimensional structure. The C鈥揅l路路路X鈥揅u interactions are absent in Cu(2CP)₂X₂, and the dimer structures of Cu(2CP)₂X₂ are linked via C鈥揅l路路路Cl鈥揅 interactions to form chain structures. This competition would indicate that C鈥揅l路路路X鈥揅u and C鈥揅l路路路Cl鈥揅 are of comparable strength. Another interesting observation, even though the two Cu(2CP)₂X₂ structures are isomorphous, is that the symmetrical C鈥揅l路路路Cl鈥揅 halogen bonding interactions play the dominant role in developing Cu(2CP)₂Br₂ crystal structures. In contrast, the perpendicular C鈥揅l路路路Cl鈥揅 halogen bonding interactions play the dominant role in the case of Cu(2CP)₂Cl₂.}