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The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Gel media have been utilized for over a century for the growth of inorganic, organic and protein crystals. [1][2][3][4][5] The improved physical characteristics of the resulting crystals (better optical quality, larger size and fewer defects) are usually ascribed to the suppression of convection currents, sedimentation and nucleation afforded by the viscous gel environment. [6][7] In many instances the gel is thought to act as an inert matrix within which crystal growth occurs, however in some cases, the gel structure has been shown to influence the polymorphism, enantiomorphism and habit of crystals. 2 Occasionally gel fibres may become incorporated into the crystal, giving rise to composite materials. 8Conventional gels are formed using polymeric or clay-like materials such as gelatine, solubility were investigated to demonstrate their potential to act as crystallisation media for molecular organic compounds. Compounds 2, and 4 have been reported previously. [23][24] Novel compounds 1 and 3 were prepared by standard methods as detailed in the supplementary information. Gelators 1 -3 were chosen because they reliably form gels in a number of solvents ranging from aqueous systems to toluene. The fibrous nature of the gels is evidenced by SEM images of the dried xerogels ( Figure 1a,b). Compound 4 is a metallogelator which forms blue coloured gels with substoichiometric amounts of CuCl 2 in methanol:water. 23 Between them, these gelators can gel a range of solvents, at different temperatures (T gel ), and with a different critical gelator concentration (CGC). This class of compound has the potential to form the basis of a library of gelators which will allow the selection of gel properties and specific functionalities to match the compound and crystallisation conditions of interest. The synthetic versatility of these gelators could also in principle allow the incorporation of tailored heteronucleating functionality. While we focus upon bis(urea) compounds, the concepts outlined herein equally apply to any LMWG.Crystallisation experiments were undertaken using a range of organic compounds of both drug and non-drug species in parallel in both gel and solution media. We undertook an initial screen using candidate compounds 2-hydroxy benzyl alcohol (HBA, 5), Aspirin (ASP, 6), carbamazepine (CBZ, 7), 1-(3-methylsulfanyl-phenyl)-3-pyridin-2-yl-urea (SPU, 8) and 1,3-bis(m-nitrophenyl)urea (NPU, 9). We then carried out a detailed study on CBZwith all gelators, and a follow up study on gelator ...

The gelation ability of a series of chiral bis(urea) gels alternates between even and odd chain length and for the even numbered spacers the rheological characteristics can be tuned by the addition of anions according to the anion binding constant.

A bis(pyridylurea) ligand (1) forms metallogels in methanol in the presence of up to 0.5 equiv of copper(II) chloride. The metallogel has been characterized using powder X-ray diffraction, SEM, and MAS NMR spectroscopic techniques. The addition of further copper(II) chloride gives the unusual crystalline 4:3 coordination polymer [Cu3(1)4Cl4]Cl2 x nH2O (2). In the presence of 0.5 equiv of copper(II) nitrate, the 2:1 crystalline coordination polymer [Cu(1)2](NO3)2 x H2O x MeOH (5) is isolated. Both 2 and 5 have been characterized by single-crystal X-ray diffraction. Complex 5 represents a possible model for the gelator and highlights key interactions with counteranions that suggest a means to tune gel properties using anion binding. The influence of chloride and acetate anions (as their NBu4+ salts) on the rheological properties of the copper(II) chloride metallogels of 1 are investigated. The rheology of the anion-containing mixtures shows complex behavior with the gel structure apparently evolving over time.

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