What's in an Atom? A Comparison of Carbon and Silicon‐Centred Amidinium⋅⋅⋅Carboxylate Frameworks**

Abstract

Despite their apparent similarity, framework materials based on tetraphenylmethane and tetraphenylsilane building blocks often have quite different structures and topologies. Herein, we describe a new silicon tetraamidinium compound and use it to prepare crystalline hydrogen bonded frameworks with carboxylate anions in water. The silicon-containing frameworks are compared with those prepared from the analogous carbon tetraamidinium: when biphenyldicarboxylate or tetrakis(4-carboxyphenyl)methane anions were used similar channel-containing networks are observed for both the silicon and carbon tetraamidinium. When terephthalate or bicarbonate anions were used, different products form. Insights into possible reasons for the different products are provided by a survey of the Cambridge Structural Database and quantum chemical calculations, both of which indicate that, contrary to expectations, tetraphenylsilane derivatives have less geometrical flexibility than tetraphenylmethane derivatives, i.e. they are less able to distort away from ideal tetrahedral bond angles. File list (3) download file view on ChemRxiv Boer et al chemrxiv manuscript.pdf (1.21 MiB) download file view on ChemRxiv Boer et al ToC.png (1.54 MiB) download file view on ChemRxiv Boer et al SI.pdf (4.35 MiB)

Room Temperature Hydrolysis of Benzamidines and Benzamidiniums in Weakly Basic Water

“…It was notable that, in both of these cases, crystallization took a long time (several days). In fact in the case of the silicon-based system, if we used higher concentrations, crystallization occurred more rapidly and we did not obtain the tetra-amide 5 , but instead obtained a hydrogen bonded salt of the tetra-amidinium …”

“…Characterization by X-ray crystallography revealed that crystals fresh from the mother liquor were the dihydrate, while thermogravimetric analysis indicated that the dried product was the monohydrate (see Supporting Information). The tetra-amidinium compounds 2 4+ and 3 4+ and the bis-amidinium 6 2+ were prepared as previously described, as were the hydrogen bonded frameworks assembled from 6 2+ and terephthalate, and from 2 4+ and tetrakis­(4-carboxyphenyl)­methane . Other compounds were bought from commercial suppliers and used as received.…”

“…In fact in the case of the silicon-based system, if we used higher concentrations, crystallization occurred more rapidly and we did not obtain the tetra-amide 5, but instead obtained a hydrogen bonded salt of the tetra-amidinium. 30 The crystal structures of 4 and 5 are isostructural and crystallize in the tetragonal space group P4 2 /n. The structures assemble through N−H•••OC amide•••amide hydrogen bonds, which have a double helical arrangement (Figure 2).…”

Room temperature hydrolysis of benzamidines and benzamidiniums in weakly basic water

“…In fact in the case of the silicon-based system, if we used higher concentrations, crystallization occurred more rapidly and we did not obtain the tetra-amide 5, but instead obtained a hydrogen bonded salt of the tetra-amidinium. 30 The crystal structures of 4 and 5 are isostructural and crystallize in the tetragonal space group P42/n. The structures assemble through N-H•••O=C amide•••amide hydrogen bonds, which have a double helical arrangement (Figure 2).…”

“…40 Characterization by X-ray crystallography revealed that crystals fresh from the mother liquor were the dihydrate, while thermogravimetric analysis indicated that the dried product was the monohydrate (see Supporting Information). The tetraamidinium compounds 2 4+ 22 and 3 4+ , 30 and the bisamidinium 6 2+ 38 were prepared as previously described, as were the hydrogen bonded frameworks assembled from 6 2+ and terephthalate, 39 and from 2 4+ and tetrakis(4carboxyphenyl)methane. 20 Other compounds were bought from commercial suppliers and used as received.…”