The Charge-Transfer Motif in Crystal Engineering. Self-Assembly of Acentric (Diamondoid) Networks from Halide Salts and Carbon Tetrabromide as Electron-Donor/Acceptor Synthons

Abstract

Unusual strength and directionality for the charge-transfer motif (established in solution) are shown to carry over into the solid state by the facile synthesis of a series of robust crystals of the [1:1] donor/acceptor complexes of carbon tetrabromide with the electron-rich halide anions (chloride, bromide, and iodide). X-ray crystallographic analyses identify the consistent formation of diamondoid networks, the dimensionality of which is dictated by the size of the tetraalkylammonium counterion. For the tetraethylammonium bromide/carbon tetrabromide dyad, the three-dimensional (diamondoid) network consists of donor (bromide) and acceptor (CBr(4)) nodes alternately populated to result in the effective annihilation of centers of symmetry in agreement with the sphaleroid structural subclass. Such inherently acentric networks exhibit intensive nonlinear optical properties in which the second harmonics generation in the extended charge-transfer system is augmented by the effective electronic (HOMO-LUMO) coupling between contiguous CBr(4)/halide centers.

Charge-transfer character of halogen bonding: Molecular structures and electronic spectroscopy of carbon tetrabromide and bromoform complexes with organic σ- and π-donors

“…Furthermore, solutions containing bromoform and either bromide or chloride as tetraalkylammonium salts showed no new bands at wavelengths higher than 250 nm; and the measurements in the far-ultraviolet spectral region (λ < 250 nm) were barred by strong component absorptions. We similarly carried out UV-Vis spectral measurements of intermolecular interactions of CBr 4 or CHBr 3 with various alkyl-substituted benzenes and polycyclic aromatics, as well as alkylamino-and methoxysubstituted benzenes containing both aromatic and heteroatom (n-donor) centers. However, only the addition of tetramethyl-p-phenylendiamine (TMPD) to the CBr 4 solution in dichloromethane led to the appearance of a clear (new) absorption band with maximum around 380 nm (which was not present in the spectrum of either the separate donor or acceptor).…”

“…3). Noticeably, this (trigonal) acceptor is crystallized in chiral space group ([P2 1 3])-in comparison with [cubic] acentric symmetry of the corresponding crystals with the tetragonal CBr 4 .…”

“…For example, halogen-bonded complexes are recognized as effective synthons for crystal engineering of nonlinear optic materials, rational drug design, chiral resolution, control of solid-state reactivity, etc. [2][3][4][5][6][7]. Furthermore, such intermolecular interactions are critical for the reactivity of halogen derivatives [1,8,9] and play important roles in biochemical systems [10].…”

“…Furthermore, halocarbon complexes have been characterized mostly as (solidstate) crystalline compounds, and there are only a few examples of the spectral appearance of new absorption bands for such complexes in solutions [4,19]. As such, the diagnostic features of donor/acceptor associates that are commonly characterized by the Mulliken dependence of their absorption bands [23] are difficult to establish unambiguously.…”

Diiodomethane as a halogen bond donor toward metal-bound halides

“…[11][12][13][14][15][16][17][18][19][20] Concurrently, halide complexes of d-metals can be employed as XB acceptors and their combination with halomethanes leads to supramolecular clusters, chains, and 3D networks. 17,18,[20][21][22] The halomethanes CBr 4 , [11][12][13][18][19][20] CHI 3 , 14,15,17,23 CHBr 3 , 11,12,20 and CFBr 3 12,19 are the most commonly used among other halomethanes in the formation of XBs with uncomplexed halides and polyhalometalate anions. Our recent works indicated that even weak XB donors such as CHCl 3 , CH 2 Cl 2 , and CH 2 Br 2 ( Fig.…”