The symmetric four-armed geometry of pentaerythrityl tetraphenyl ether (5) makes it a valuable starting point for building complex molecular and supramolecular structures. In particular, it provides a core to which multiple sites of attractive intermolecular interaction can be attached, thereby creating compounds predisposed to form complex networks by association. To facilitate exploitation of the pentaerythrityl tetraphenyl ether core in such ways, we have prepared more than 20 new derivatives by efficient methods. Of special interest are compounds 3 and 4, which incorporate four diaminotriazine groups attached to the meta and para positions of the pentaerythrityl tetraphenyl ether core. Crystallization of compounds 3 and 4 from DMSO/dioxane is directed by hydrogen bonding of the diaminotriazine groups according to well-established motifs, thereby producing three-dimensional networks. In forming these networks, each molecule of compound 3 forms a total of 12 hydrogen bonds with six others, whereas each molecule of compound 4 forms a total of 16 hydrogen bonds with four others. Both networks are highly porous and define significant interconnected channels for the inclusion of guests. In crystals of compounds 3 and 4, the fraction of the volume accessible to guests is 66% and 57%, respectively. In both cases, the pentaerythrityl tetraphenyl ether cores adopt conformations that deviate substantially from tetrahedral geometry. It is noteworthy that the inherent flexibility of the core does not favor the formation of close-packed guest-free structures.

Tetraphenylmethane, tetraphenylsilane, and simple derivatives with substituents that do not engage in hydrogen bonding typically crystallize as close-packed structures with essentially no space available for the inclusion of guests. In contrast, derivatives with hydrogen-bonding groups are known to favor the formation of open networks that include significant amounts of guests. To explore this phenomenon, we synthesized six new derivatives 5a–5e and 6a of tetraphenylmethane and tetraphenylsilane with urethane and urea groups at the para positions, crystallized the compounds, and determined their structures by X-ray crystallography. As expected, all six compounds crystallize to form porous three-dimensional hydrogen-bonded networks. In the case of tetraurea 5e, 66% of the volume of the crystals is accessible to guests, and guests can be exchanged in single crystals without loss of crystallinity. Of special note are: (i) the use of tetrakis(4-isocyanatophenyl)methane (1f) as a precursor for making enantiomerically pure tetraurethanes and tetraureas, including compounds 5b, 5c; and (ii) their subsequent crystallization to give porous chiral hydrogen-bonded networks. Such materials promise to include chiral guests enantioselectively and to be useful in the separation of racemates, asymmetric catalysis, and other applications.Key words: crystal engineering, molecular tectonics, hydrogen bonding, networks, porosity, urethanes, ureas, tetraphenylmethane, tetraphenylsilane.

A series of new metal-organic frameworks have been constructed by the coordination of Cu(II) and Cu(I) with pentaerythrityl tetrakis(4-pyridyl) ether (1 = PETPE), a flexible tetradentate ligand. Networks derived from Cu(OOCCH(3))(2), Cu(NO(3))(2), and CuBF(4) proved to have different topologies (diamondoid, PtS, and SrAl(2), respectively). This reflects (1) the ability of PETPE (1) to adopt diverse conformations and (2) the varied geometries of complexes of Cu(II) and Cu(I). Extended PETPE (2), a tetrapyridine with phenyl spacers inserted into the pentaerythrityl core of PETPE (1), yielded an expanded version of the PtS network derived from simple PETPE (1) and Cu(NO(3))(2). However, increases in the ability of the network to accommodate guests were largely offset by interpenetration of independent networks. Attempts to thwart interpenetration by converting ligand 2 into methyl-substituted derivative 3 led to the construction of networks with alternative topologies. In particular, the reactions of ligand 3 with both Cu(II) and Cu(I) yielded isostructural Pt(3)O(4) networks, despite the preference of the two oxidation states for coordination spheres with different geometries. Together, these observations demonstrate that PETPE (1) and related compounds are useful ligands for constructing metal-organic frameworks, with a distinctive ability to accommodate a single metal in different oxidation states, as well as to adapt to a metal in a single oxidation state but with different counterions or secondary ligands.

Molecules that associate to form porous networks can be made by attaching multiple hydrogen-bonding sites to suitable cores. Pentaerythrityl tetraphenyl ether, a four-armed core, is the progenitor of dendritic derivatives with more arms, including dipentaerythrityl hexaphenyl ether 7. An advantage of such dendritic derivatives is that the resulting networks are held together by larger numbers of intermolecular hydrogen bonds. [structure: see text]

A series of compounds with multiple PhNH 2 groups were synthesized and crystallized, and their structures were solved by X-ray diffraction to assess the ability of -NH 2 groups in anilines to direct molecular crystallization. 2,2′,7,7′-Tetraamino-9,9′-spirobi[9H-fluorene] (1c) forms an inclusion complex held together in part by donation of hydrogen bonds from -NH 2 groups to guest molecules. Surprisingly, the -NH 2 groups do not engage in hydrogen bonding with each other. Tetrakis(4-aminophenyl)methane (2c) crystallizes to form a guest-free closepacked diamondoid network in which each -NH 2 group donates and accepts one N-H‚‚‚N hydrogen bond. Tetrakis-[(4-aminophenoxy)methyl]methane (3c), a more flexible analogue, also crystallizes as a close-packed structure maintained by an extensive network of N-H‚‚‚N hydrogen bonds. Despite the structural similarity of tetraanilines 2c and 3c, their hydrogen-bonding patterns and network topologies are different. A flexible hexaaniline, 1,1′-oxybis-[3-(4-aminophenoxy)-2,2-bis[(4-aminophenoxy)methyl]]propane (4c), produces a close-packed network joined by both N-H‚‚‚N and N-H‚‚‚O hydrogen bonds. Tetrakis(4-aminophenyl)ethylene ( 5) crystallizes as a hydrate to yield a structure consisting of layered hydrogen-bonded sheets. The diverse hydrogen-bonding motifs observed show that crystal engineering using direct interactions of the -NH 2 group of anilines is a challenging endeavor, and other intermolecular interactions can compete effectively with N-H‚‚‚N hydrogen bonds to determine how crystallization occurs.