Variable Pore Size, Variable Chemical Functionality, and an Example of Reactivity within Porous Phenylacetylene Silver Salts

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Abstract

Investigations on molecular variants of the 3-fold symmetric 1,3,5-tris(4-ethynylbenzonitrile)benzene crystallized with silver triflate revealed a nearly invariant pseudohexagonal porous structure type. Modifications involved the attachment of pendant groups to the central aromatic ring of the parent molecule. Pendant groups include the vinyl group, stilbene, the chiral group myrtanol, and groups with different chemical functionalities such as alcohols, ethers, and esters. Modifications also included the addition of elongated spacer units between the central benzene ring and the peripheral nitrile groups. In these molecules the acetylene bridges of 1,3,5-tris(4-ethynylbenzonitrile)benzene were replaced with diacetylene, ethynylbenzene, and diethynylbenzene type units. Single-crystal refinements for pentoxy-2,4,6-tris(4-ethynylbenzonitrile)benzene·AgOTf and 1,3,5-tris(4-(4-ethynylbenzonitrile)phenyl)benzene·AgOTf as well as powder data on 12 crystalline phases showed the consistent formation of pseudohexagonal channels, demonstrating that the parent porous architecture is stable both to functional modification of the interior of the channel as well as to enlargement of the pores. Pentoxy-2,4,6-tris(4-ethynylbenzonitrile)benzene·AgOTf refined in the monoclinic space group Am. 1,3,5-Tris(4-(4-ethynylbenzonitrile)phenyl)benzene·AgOTf was found to be triclinic with space group P1̄. These crystals have pseudohexagonal channels respectively 15 and 25 Å in diameter. Cell constants based on powder data are compatible with channel diameters ranging from 10 to 30 Å. The latter channel diameters are among the largest known for organic porous solids. The introduction of the chiral myrtanol unit led to the preparation of a chiral porous solid. The thermal and chemical stabilities of these phases were investigated. The pseudohexagonal structure proved stable to complete solvent loss from the channel. It was found in the case of a host with alcohol functionality that an acid anhydride guest, trifluoroacetic anhydride, reacted with the host to form an ester with retention of the porous structure type.

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