Analysis of rapidly synthesized guest-filled porous complexes with synchrotron radiation: practical guidelines for the crystalline sponge method

Abstract

This report describes complete practical guidelines and insights for the crystalline sponge method, which have been derived through the first use of synchrotron radiation on these systems, and includes a procedure for faster synthesis of the sponges. These guidelines will be applicable to crystal sponge data collected at synchrotrons or in-house facilities, and will allow researchers to obtain reliable high-quality data and construct chemically and physically sensible models for guest structural determination.

The crystalline sponge method: a solvent-based strategy to facilitate noncovalent ordered trapping of solid and liquid organic compounds

“…3 Target compounds ( 2 – 5 ) were commercially obtained and solvated to maximum concentration up to 0.5 M in MTBE at room temperature ( 2 : 0.14 M, 3 : 0.5 M, 4 : 0.5 M, 5 : 0.07 M) (these are unoptimized; therefore it is possible to use lower concentrations), and 2 was also dissolved in CHCl 3 at 0.5 M for comparison. For guest inclusion, multiple crystals of 1 ·CHCl 3 were placed into a vial and the residual CHCl 3 was removed through careful pipetting.…”

“…For 1 · 4 , the loop was mounted on a Bruker D8 three-circle fixed χ goniometer with an APEX II charge coupled device (CCD) detector and an Oxford Cryostream generated 100 K N 2 cold stream at experimental station 15-ID-B, 12 where a wavelength of ~0.41 Å was used with a 0.2 s exposure time, and data was collected with multiple ϕ scans at 0.5° increments with ω offsets using a 7 cm detector distance. It is important to mention that the new experimental setup at station 15-ID-D allowed collection times of ~5–24 minutes, which is at least a 40–90% reduction in time versus prior crystal sponge synchrotron data collected by us at 15-ID-B, 3,4,12 and is roughly a 150–720–fold improvement in time versus collecting datasets using a typical in-house diffractometer with a sealed-tube anode source and a CCD detector (assuming a 2.5 day collection with 2 min/frame exposure time). 11,13 Evaluation of the initial diffraction images and reciprocal lattice construction was performed to ascertain crystal quality.…”

“…Our work in this area has focused on improving the operational ease and reliability of the technique by reducing host preparation time, establishing crystallographic guidelines to ensure that chemically and physically-sensible models are constructed from high-quality data, and investigating the beneficial effects of changing the MOF terminal halide ligand. 3,4 …”

“…3 However, the ability to trap amorphous and crystalline solids in a rapid and operationally simple fashion in 1 ·CHCl 3 , which is easy and fast to synthesize, would expand the scope of compounds that can be analysed. Inclusion of crystalline solids is important if the native crystals exhibit poor shape (habit), diffract poorly, are prone to problematic twinning, or one wishes to determine absolute configuration of a molecule that does not contain heavy atoms and access to a diffractometer with a CuKα radiation source is unavailable.…”

“…With extensive disorder and low occupancies it could also be possible to confuse residual solvent as target molecules if the target contains cyclohexyl rings, complicating structure refinement. 3 In addition, cyclohexane (polarity index: 0, water insoluble) 8 is not an optimal solvent for dissolving a wide array of compounds even if a small quantity of halogenated solvent is added. A recent report by Santarsiero and co-workers describing the fastest synthesis of 1 ·PhNO 2 to date noted the use of n -Bu 2 O to solvate liquid diisopropylaniline for inclusion.…”