K. Travis Holman

We demonstrate a systematic application of the mechanochemical liquid-assisted grinding (LAG) methodology to screen for forms of zinc imidazolate (ZnIm₂), of fundamental importance as the simplest member of the zeolitic imidazolate framework materials family. The exploration of 45 different liquid additives, selected based on their molecular structure and physicochemical properties has resulted in eight different ZnIm₂ topological forms, appearing in 13 crystallographically distinct solid forms (including two previously unknown forms of the crb (BCT) topology), amorphous phases, and the interrupted moc-Zn₄Im₈HIm. All prepared topological forms were also explored computationally, using dispersion-corrected periodic density functional theory (DFT) calculations, enabling the rationalization of screening outcomes, and setting the stage for future prediction of additive-directed metal-organic framework (MOF) synthesis. This first systematic exploration of LAG in screening for three-dimensional MOFs demonstrates the potential of the liquid additive to not only accelerate materials synthesis, but also to direct it toward topologically different MOFs. The discovery of novel forms of a material that already exhibits at least 21 crystallographically and functionally different forms provides a strong testimony on the power of mechanochemistry in metal-organic materials discovery.

We demonstrate a systematic application of the mechanochemical liquid-assisted grinding (LAG) methodology to screen for forms of zinc imidazolate (ZnIm2), of fundamental importance as the simplest member of the zeolitic imidazolate framework materials family. The exploration of 45 different liquid additives, selected based on their molecular structure and physicochemical properties has resulted in seven different ZnIm2 topologies, appearing in 12 structurally distinct solid forms (including two previously unknown forms of the crb (BCT) topology), amorphous phases, and the interrupted moc topology material. All prepared topologies were also explored computationally, using dispersion-corrected periodic density functional theory (DFT) calculations, enabling the rationalization of screening outcomes, and setting the stage for future prediction of additive-directed MOF synthesis. This first systematic exploration of LAG in screening for three-dimensional metal-organic frameworks demonstrates the potential of the liquid additive to not only accelerate materials synthesis, but also to direct it towards topologically different frameworks. The ability to discover novel forms in a material that already exhibits at least 21 crystalographically and functionally different forms provides a strong testimony on the power of mechanochemistry in metal-organic materials discovery.

η⁶‐Metalated aryl halides are recognized as a class of halogen bond (XB) donors. Click‐like η⁶‐metalation/demetalation of aryl iodides by cyclopentadienylruthenium(II) ([CpRu^II]⁺) is shown to turn ON/OFF (amplify/suppress) XB donor functionality. [CpRu(MeCN)₃][PF₆] is shown to react quantitatively with iodobenzenes (ArI_n, n=1,2) to yield [CpRu(η⁶‐ArI_n)][PF₆] compounds. Photochemical demetalation (405 nm) quantitatively reverts these compounds to ArI_n and [CpRu(MeCN)₃][PF₆]. Crystal structures of [CpRu(ArX_n)]⁺ salts show that the [CpRu(ArI_n)]⁺ cations are strong, charge‐assisted XB donors analogous to iodopyridinium cations. XB‐induced association of [CpRu(C₆H₅I)]⁺ with diazobicyclo[2.2.2]octane (DABCO) is established by NMR spectroscopy. [CpRu(C₆H₅I)][BPh₄] and [CpRu(1,4‐C₆H₄I₂)][BPh₄] co‐crystallize with DABCO and the structure of [CpRu(1,4‐C₆H₄I₂)][BPh₄]⋅DABCO⋅Et₂O is reported. DFT calculations support amplification of the XBing capabilities of aryl iodides upon [CpRu]⁺‐metalation.

η⁶‐Metalated aryl halides are recognized as a class of halogen bond (XB) donors. Click‐like η⁶‐metalation/demetalation of aryl iodides by cyclopentadienylruthenium(II) ([CpRu^II]⁺) is shown to turn ON/OFF (amplify/suppress) XB donor functionality. [CpRu(MeCN)₃][PF₆] is shown to react quantitatively with iodobenzenes (ArI_n, n=1,2) to yield [CpRu(η⁶‐ArI_n)][PF₆] compounds. Photochemical demetalation (405 nm) quantitatively reverts these compounds to ArI_n and [CpRu(MeCN)₃][PF₆]. Crystal structures of [CpRu(ArX_n)]⁺ salts show that the [CpRu(ArI_n)]⁺ cations are strong, charge‐assisted XB donors analogous to iodopyridinium cations. XB‐induced association of [CpRu(C₆H₅I)]⁺ with diazobicyclo[2.2.2]octane (DABCO) is established by NMR spectroscopy. [CpRu(C₆H₅I)][BPh₄] and [CpRu(1,4‐C₆H₄I₂)][BPh₄] co‐crystallize with DABCO and the structure of [CpRu(1,4‐C₆H₄I₂)][BPh₄]⋅DABCO⋅Et₂O is reported. DFT calculations support amplification of the XBing capabilities of aryl iodides upon [CpRu]⁺‐metalation.

The macrocyclic cavitand MeMeCH₂ is used as a template for the mechanochemical synthesis of 0.2MeMeCH₂@RHO-Zn₁₆(Cl₂Im)₃₂ (0.2MeMeCH₂@ZIF-71) and RHO-ZnBIm₂ (ZIF-11) zeolitic imidazolate frameworks (ZIFs). It is shown that MeMeCH₂ significantly accelerates the mechanochemical synthesis, providing high porosity products (BET surface areas of 1140 m²/g and 869 m²/g, respectively). Templation of RHO-topology ZIF frameworks constructed of linkers larger than benzimidazole (HBIm) was unsuccessful. It is also shown that cavitands other than MeMeCH₂—namely MeHCH₂, Me i BuCH₂, HPhCH₂, MePhCH₂, BrPhCH₂, BrC5CH₂—can serve as effective templates for the synthesis of x(cavitand)@RHO-ZnIm₂ products. The limitations on cavitand size and shape are explored in terms of their effectiveness as templates.

We demonstrate a simple method for real-time monitoring of mechanochemical synthesis of metal–organic frameworks, by measuring changes in pressure of gas produced in the reaction. Using this manometric method to monitor the mechanosynthesis of the zeolitic imidazolate framework ZIF-8 from basic zinc carbonate reveals an intriguing feedback mechanism in which the initially formed ZIF-8 reacts with the CO₂ byproduct to produce a complex metal carbonate phase, the structure of which is determined directly from powder X-ray diffraction data. We also show that the formation of the carbonate phase may be prevented by addition of excess ligand. The excess ligand can subsequently be removed by sublimation, and reused. This enables not only the synthesis but also the purification, as well as the activation of the MOF to be performed entirely without solvent.

Guanidinium organosulfonates (GSs) are a large and well‐explored archetypal family of hydrogen‐bonded organic host frameworks that have, over the past 25 years, been regarded as nonporous. Reported here is the only example to date of a conventionally microporous GS host phase, namely guanidinium 1,4‐benzenedisulfonate (p‐G₂BDS). p‐G₂BDS is obtained from its acetone solvate, AcMe@G₂BDS, by single‐crystal‐to‐single‐crystal (SC‐SC) desolvation, and exhibits a Type I low‐temperature/pressure N₂ sorption isotherm (SA_BET=408.7(2) m² g⁻¹, 77 K). SC‐SC sorption of N₂, CO₂, Xe, and AcMe by p‐G₂BDS is explored under various conditions and X‐ray diffraction provides a measurement of the high‐pressure, room temperature Xe and CO₂ sorption isotherms. Though p‐G₂BDS is formally metastable relative to the “collapsed”, nonporous polymorph, np‐G₂BDS, a sample of p‐G₂BDS survived for almost two decades under ambient conditions. np‐G₂BDS reverts to zCO₂@p‐G₂BDS or yXe@p‐G₂BDS (y,z=variable) when pressure of CO₂ or Xe, respectively, is applied.

Guanidinium organosulfonates (GSs) are a large and well‐explored archetypal family of hydrogen‐bonded organic host frameworks that have, over the past 25 years, been regarded as nonporous. Reported here is the only example to date of a conventionally microporous GS host phase, namely guanidinium 1,4‐benzenedisulfonate (p‐G₂BDS). p‐G₂BDS is obtained from its acetone solvate, AcMe@G₂BDS, by single‐crystal‐to‐single‐crystal (SC‐SC) desolvation, and exhibits a Type I low‐temperature/pressure N₂ sorption isotherm (SA_BET=408.7(2) m² g⁻¹, 77 K). SC‐SC sorption of N₂, CO₂, Xe, and AcMe by p‐G₂BDS is explored under various conditions and X‐ray diffraction provides a measurement of the high‐pressure, room temperature Xe and CO₂ sorption isotherms. Though p‐G₂BDS is formally metastable relative to the “collapsed”, nonporous polymorph, np‐G₂BDS, a sample of p‐G₂BDS survived for almost two decades under ambient conditions. np‐G₂BDS reverts to zCO₂@p‐G₂BDS or yXe@p‐G₂BDS (y,z=variable) when pressure of CO₂ or Xe, respectively, is applied.

We report the first use of a non-ionic solid (NIS) as a template in mechanosynthesis of a metal-organic framework. Via eight intermolecular C-H∙∙∙O hydrogen bonds, the macrocyclic MeMeCH₂ template predictably functions as a 'shoe-last' for the assembly of double-eight rings (d8rs) in the liquid-assisted reaction of ZnO and imidazole (ImH). The resulting new form of ZnIm₂ (namely xMeMeCH₂@RHO-Zn₁₆Im₃₂) exhibits high porosity, is thermally stable, and is available in multi-gram amounts.