A Supramolecular Approach to Organic Alloys: Cocrystals and Three‐ and Four‐Component Solid Solutions of 1,4‐Diazabicyclo[2.2.2]octane and 4‐X‐Phenols (X=Cl, CH₃, Br)

Abstract

Herein, we describe the preparation of binary cocrystals and ternary and quaternary solid solutions of 1,4-diazabicyclo-[2.2.2]octane (DABCO) and 4-X-phenols (X = Cl, CH 3 , Br). Multicomponent solids, be they cocrystals or solid solutions, are materials that may exhibit new or superior functionalities relative to the individual components.[1] Though molecular complexes have been studied for a long time, [1][2][3] the design of cocrystals containing more than two different components remains a challenging task.[4] Except for a few notable contributions, [5] most studies on organic cocrystals led only to the formation of binary organic solids.[1] In contrast, metals and inorganic compounds readily form multicomponent solids in the form of solid solutions.[6] Creating multicomponent solid solutions of organic molecules, however, is challenging because these molecules possess intricate shapes and participate in directional intermolecular interactions. [3] Not surprisingly, most molecule-based solid solutions contain only two components. [7] We describe a supramolecular approach for the preparation of solid solutions that contain three or more organic molecules. The principal advantage of solid solutions is that their properties can be modulated by the gradual modification of the relative ratio of the components.[8]Scheme 1 shows our approach to the formation of organic alloys. We begin with a trimolecular motif wherein a central molecule (A) is connected to two peripheral molecules (B or C) through similar intermolecular interactions. If the two peripheral molecules are identical, the binary cocrystals AB 2 or AC 2 are formed. If they are different, a ternary cocrystal BAC or a ternary solid solution A(B n C 1Àn ) 2 (0 < n < 1) can be formed, depending on the similarity of the sizes and shapes of the peripheral molecules. Adding another isosteric component (D) can lead to a quaternary solid solution A(B n C m D p ) 2 (n + m + p = 1, 0 < n, m, p < 1).We use DABCO as the central molecule and 4-X-phenols (X = Cl, CH 3 , Br) as the peripheral molecules (Scheme 2). The chloro, methyl, and bromo substituents of the 4-Xphenols have similar shapes and comparable sizes (20, 24, and 28 3 ), [9] and do not interfere with the O À H···N hydrogen bonding required for the trimolecular assembly. We surmised that the size, shape, and chemical similarity of the 4-Xphenols would enable the formation of solid solutions upon crystallization of DABCO with two or three of the phenols. We call these crystalline materials supramolecular solid solutions because their repeat unit is a trimolecular assembly.[10]Single crystals of binary cocrystals and of ternary and quaternary solid solutions (having equimolar ratios of phenols) suitable for X-ray diffraction were grown from benzene solutions (Table 1; Scheme 2).[11] The binary cocrystals ClCl and MeMe are isostructural; [12] Figure 1 a shows the structure of ClCl. The unit cell of MeMe is larger than that of ClCl, in accordance with the larger size of the methyl groups relative to the chlo...

Porous Organic Alloys

“…These data show that CC1 , CC3 ‐ R , and CC4 ‐ R combine to form a non‐stoichiometric solid solution, or an “organic alloy”,2f,h where CC3 and CC4 can be interchanged substitutionally into half of the sites of the cubic lattice. It is therefore possible to incorporate any relative ratio of the CC3 ‐ R and CC4 ‐ R modules without affecting the basic packing mode.…”

Isostructural Materials Achieved by Using Structurally Equivalent Donors and Acceptors in Halogen‐Bonded Cocrystals

“…In the context of materials design, we notice that the isostructurality of the seven cocrystals also enables further fine-tuning of the properties of the solids, through the formation of solid solutions. [34] That pure cocrystal components adopt different crystal structures in the solid state [25,26] suggests isostructurality is facilitated by cocrystallization and halogen-bond formation. To understand how halogen bonding might help overcome shape and functionality differences between individual cocrystal components, we are now exploring further halogen-bonded cocrystal systems.…”

Formation of isostructural solid solutions in 2,6-disubstitutedN-phenylformamides andN-phenylthioamides

“…A phenomenon that arises from crystallization of chemically similar molecules, and one that is also known to be common for organic compounds and salts, is isostructurality (Galcera et al, 2013;Wood et al, 2012;Dabros et al, 2007;James et al, 2012). Factors such as the balance between 'closepacking effects' and more directional and anisotropic intermolecular interactions during crystallization (Aakerö y et al, 2010) play an important role in the engineering of isostructural crystals.…”

“…Factors such as the balance between 'closepacking effects' and more directional and anisotropic intermolecular interactions during crystallization (Aakerö y et al, 2010) play an important role in the engineering of isostructural crystals. Experiments involving the crystallization of two different compounds mixed in solution, or ground together without solvent, often result in solid solutions, some containing three or more organic molecules (Dabros et al, 2007) or mixed solid solutions that adopted the structure of one of the pure starting materials. Mechanochemical preparations of co-crystals, conducted by grinding solid reactants together with minimal solvent, have been shown to be one of the most practical and beneficial methods, often yielding products that are not obtainable by solution-based methods (James et al, 2012).…”