Victoria A. Russell

Two-dimensional hydrogen-bonded assemblies: the influence of sterics and competitive hydrogen bonding on the structures of guanidinium arenesulfonate networks

Guanidinium and organosulfonate ions self-assemble into crystalline lattices described by robust two-dimensional hydrogen-bonded networks with the general formula [C(NH 2 ) 3 ] + RSO 3 - . These networks, which typically have quasihexagonal symmetry due to favourable hydrogen bonding between six guanidinium proton donors and six sulfonate electron lone pair acceptors, assemble in the third dimension by stacking in a manner which maximizes van der Waals interactions between R groups. The steric requirements of the R groups dictate whether this assembly results in interdigitated bilayer stacking in which all the R groups are orientated to one side of a given sheet or interdigitated single layer stacking in which R groups are orientated to both sides of a given hydrogen-bonded sheet. The two-dimensional network tolerates very different steric requirements of the R groups due to the ability to form either of these stacking motifs and to the inherent flexibility of the hydrogen-bonded network about one-dimensional hydrogen-bonding ‘hinges’. This flexibility allows the sheets to pucker in order to accommodate steric strain between R groups within the layers. We describe here the influence of substituents on the R groups whose steric and hydrogen bonding capacity influence the puckering of the two-dimensional guanidinium sulfonate network. In particular, we examine the X-ray crystal structures of the guanidinium salts of ferrocenesulfonate and methyl- and nitro-substituted benzenesulfonates. The retention of the hydrogen-bonding motif in spite of steric and hydrogen bonding interference by the R group substituents illustrates the robustness of the guanidinium sulfonate network. However, additional competing hydrogen bonding and sterics influence the crystal packing, and in the case of multiple substituents on the R groups, these factors may disrupt the guanidinium sulfonate network. Overall, this work demonstrates that the use of robust two-dimensional supramolecular modules can reduce the crystal engineering problem to the last remaining dimension, which can simplify the design of functional molecular materials.

Solid-State Structure of a Layered Hydrogen-Bonded Salt: Guanidinium 5-Benzoyl-4-hydroxy-2-methoxybenzenesulfonate Methanol Solvate

Guanidinium 5-benzoyl-4-hydroxy-2-methoxybenzene-sulfonate methanol solvate [C(NH2)3+.(C14H11O3)SO3−.CH3OH] crystallizes into a layered structure containing a two-dimensional hydrogen-bonded network typical of guanidinium alkane- and arenesulfonates. All six guanidinium protons and six sulfonate oxygen lone-pair acceptors participate in hydrogen bonding to form nearly planar pseudohexagonal hydrogen-bonded sheets, which can be viewed as parallel connected hydrogen-bonded ribbons. The 5-benzoyl-4-hydroxy-2-methoxybenzene groups are oriented to the same side of each ribbon, but the orientation of these groups on adjacent ribbons alternates with respect to the hydrogen-bonded sheet. The planar sheets stack with interdigitation of the arene groups, resulting in a structure in which layers of 5-benzoyl-4-hydroxy-2-methoxybenzene groups are separated by ionic hydrogen-bonded sheets. Each methanol molecule forms a hydrogen bond to one of the sulfonate O atoms, resulting in this oxygen forming a total of three hydrogen bonds, and fills void volume between the interdigitated 5-benzoyl-4-hydroxy-2-methoxybenzene groups of neighboring sheets. The benzophenone hydroxyl proton forms an intramolecular hydrogen bond to the carbonyl oxygen.

Interweaving of two-dimensional hydrogen-bonded networks directed by chloride ions

A novel mixed anion complex has been prepared in the course of crystal engineering studies of guanidinium organosulfonates. Bis(guanidinium) ethanesulfonate chloride, {[C(NH2)3]+}2CH3CH2SO3-Cl-, assembles into a crystalline lattice which exhibits structural characteristics reminiscent of both of its monoanion counterparts guanidinium chloride and guanidinium ethanesulfonate. The structure nominally contains two-dimensional (001) hydrogen-bonded sheets resembling those found in guanidinium organosulfonates, but in which chloride ions replace half of the sulfonate ions. The (001) sheets consist of alternating guanidinium-sulfonate and guanidinium-chloride hydrogen-bonded ribbons, linked together by guanidinium-sulfonate and guanidinium-chloride hydrogen bonds. The presence of chloride ions in the (001) sheets expands this network to enable interweaving of a second hydrogen-bonded sheet, consisting only of guanidinium and chloride ions, orthogonal to the (001) sheets. The interweaving also is made possible by the isotropic nature of the chloride ion with respect to hydrogen bonding.

“Crystal Engineering” with Two-Dimensional Hydrogen Bonding Networks

One approach toward controlling the assembly of molecules into predictable crystalline architectures involves the use of higher dimensional supramolecular networks that are resilient toward changes in ancillary functional groups attached to molecular constituents of the network. The use of n-dimensional networks facilitates the design and synthesis of new materials by reducing crystal engineering to 3- n dimensions. We describe herein the assembly of adjustable and highly porous host lattices based on robust two-dimensional guanidinium-sulfonate hydrogen bonded networks. The resilience of this network allows facile prediction of crystal structure, including architectural isomers that can be directed by judicious choice of guest molecules in solution. Two architectural isomers, a pillared bilayer form and a pillared brick form, have substantial porosity that is sustained by a diverse variety of guest molecules. Notably, the brick frameworks have packing fractions (without guest), nominally twice that of the bilayer materials. Molecular host lattices with nanometer scale porosity provide substantial opportunities in areas including crystallization-based chemical separations, synthesis of new functional materials, and topochemically-directed reactions.