Search

Preferential trapping of a selected metal-oxoanion from a mixture of other metal-oxoanionic toxic pollutants in water has been demonstrated by implementing energy-efficient adsorption followed by the ion-exchange method, utilizing a hydrolytically stable cationic metal–organic framework (MOF). The cationic MOF exhibits ultrafast and selective extraction efficiency towards ReO4− (a surrogate anion of radioactive TcO4−) over other metal-oxoanions in contaminated water systems. [ABSTRACT FROM AUTHOR]

Over the last few decades, given the impending global energy and environmental crises, paramount development in nuclear energy as an alternative high power density and low-carbon energy source has been widely observed. However, this development is hindered due to certain problems associated with nuclear reactors, including the emission of volatile radioactive substances, like organic iodides and iodine, which must be eliminated before releasing the off-gas. These substances include methyl iodide (CH3I), ethyl iodide (CH3CH2I), and iodine, which are exceedingly harmful to both the environment and human health. Although several porous solid adsorbents have been successfully employed to sequester organic iodides (generally CH3I) from the vapor phase, the majority of the earlier investigations have largely focused on the saturation capacity and kinetic study of CH3I capture. However, the importance of the porous adsorbents' strategic functions in the unique binding interaction with organic iodides has been grossly underappreciated and poorly understood. Also, certain crucial difficulties pertaining to the practical capturing of radioactive organic iodides from nuclear waste were thwarted in the endeavors to construct innovative adsorbents. Herein, we have demonstrated a systematic strategy-driven study to understand the roles of framework-integrated functionalities towards organic iodide sequestration by varying the number of N-heteroatomic sites in a series of chemically stable porous covalent organic frameworks (COFs). The CH3I adsorption capacity was found to be positively correlated with the porosity or surface area as well as with the N-heteroatomic or heterocyclic functionalities, such as the imine, pyridine, and triazine sites of these COFs. Under both static and dynamic conditions, all the COFs exhibited high CH3I sorption capacities through the N-methylation reaction mechanism. This work is of fundamental importance to understanding the CH3I adsorption mechanisms and also offers direction for the design and development of novel adsorbents for relevant applications. [ABSTRACT FROM AUTHOR]

Metal–organic frameworks (MOFs) have been a research hotspot for the last two decades, witnessing an extraordinary upsurge across various domains in materials chemistry. Ionic MOFs (both anionic and cationic MOFs) have emerged as next-generation ionic functional materials and are an important subclass of MOFs owing to their ability to generate strong electrostatic interactions between their charged framework and guest molecules. Furthermore, the presence of extra-framework counter-ions in their confined nanospaces can serve as additional functionality in these materials, which endows them a significant advantage in specific host–guest interactions and ion-exchange-based applications. In the present review, we summarize the progress and future prospects of iMOFs both in terms of fundamental developments and potential applications. Furthermore, the design principles of ionic MOFs and their state-of-the-art ion exchange performances are discussed in detail and the future perspectives of these promising ionic materials are proposed. [ABSTRACT FROM AUTHOR]

Thanks to a bottom-up design of metals and organic ligands, the library of metal–organic frameworks (MOFs) has seen a conspicuous growth. Post-synthetically modified MOFs comprise a relatively smaller subset of this library. Whereas the approach of post-synthetic modification was seminally introduced for MOFs in the early 1990s, the earliest examples of post-synthetically modified MOFs are only congruous with adsorption and catalysis. The utility of PSM-derived MOFs for the sensing and capture of water contaminants is relatively niche. Arguably though, an increasing number of post-synthetically modified MOFs are finding relevance in the context of water pollutant remediation. In this article, we review the recent advances in this area and propose a structure–function relationship-guided blueprint for the future outlook. [ABSTRACT FROM AUTHOR]

Water pollution from heavy metals and their toxic oxo-anionic derivatives such as CrO42−, Cr2O72−, HAsO42−, and HAsO32− has become one of the most critical environmental issues. To address this, herein, we report a new hydrolytically stable luminescent Zn(II) based cationic metal organic framework (MOF), iMOF-4C, which further successfully exhibited a rare dual "turn off/on" fluorescence response toward Cr(VI), As(V) and As(III) based oxo-anions respectively in water medium. In addition, iMOF-4C was found to maintain its superior selectivity in the presence of other concurrent anions (e.g. SO42−, Cl−, Br−, ClO4−, NO3−, SCN− and CO32−). More importantly, iMOF-4C exhibited an excellent selective and sensitive luminescence "turn-off" response towards CrO42− and Cr2O72− anions in water medium with the quenching constant (Ksv) values as high as 1.31 × 105 M−1 (CrO42−) and 4.85 × 105 M−1 (Cr2O72−), which are found to be the highest among the values reported in the regime of MOFs. Interestingly, iMOF-4C showed fluorescence "turn-on" response toward HAsO42− and HAsO32− with an enhancement coefficient (Kec) of 1.98 × 104 M−1 and 3.56 × 103 M−1 respectively. The high sensitivity and low detection limits make iMOF-4C more feasible for real-time sensing of such toxic oxo-anions in an aqueous medium. Furthermore, the probable sensing mechanism has been investigated by DFT calculation studies and discussed in detail. [ABSTRACT FROM AUTHOR]

Designing selective sorbent materials to sequestrate toxic oxo-anions having weaker binding tendency, for instance oxo-anions of selenium and arsenic (Se(IV)/Se(VI)/As(V)), is an arduous challenge. Herein, we demonstrate the molecular shape recognition aided synthesis of a chemically stable cationic MOF (iMOF-3C) which exhibits fast, selective removal behavior (∼99% in 5 min) towards toxic oxo-anions of Se(VI)/As(V)/Se(IV) even at ultralow concentrations (∼1000 ppb). The cationic network illustrates superior performance in the presence of interfering ions, viz. CO32− and SO42−, which was further validated by exceptional distribution coefficient values Kd > 106 mL g−1. The maximum uptake capacity stands among the best performing materials reported in the domain of ionic MOFs (iMOFs). Furthermore, iMOF-3C successfully performs in complicated systems such as river water to yield drinking quality water as per the WHO and US EPA standards. The exceptional binding ability was corroborated by DFT calculations (high binding energies) that also aid in visualizing the binding sites for the entrapped oxo-anions. [ABSTRACT FROM AUTHOR]

A highly chemically stable porous covalent framework (PCF-1) based on ether linkages has been synthesized, which exhibits no loss up to ∼500 °C along with retention of integrity under acidic, basic and oxidative reagent conditions. Owing to its thermal and chemical stability, post-synthetic covalent modification was executed for the introduction of pendant sulphonic acid (–SO3H) groups. The covalently modified compound (PCF-1-SO3H) presents a remarkably high conductivity (ca. 0.026 S cm−1), with an ∼130 fold enhancement in proton conductivity over the parent compound. This value is comparable with those of commercially used Nafion-based proton conducting materials and stands as the highest known value in the regime of post-synthetically modified porous organic frameworks. It is noteworthy to mention that PCF-1 is stable in both acidic and alkaline media, which is not commonly observed for most of the porous materials trialed as proton conducting materials, including metal–organic frameworks. [ABSTRACT FROM AUTHOR]

Metal–organic frameworks (MOFs) or porous coordination polymers (PCPs) are open, crystalline supramolecular coordination architectures with porous facets. These chemically tailorable framework materials are the subject of intense and expansive research, and are particularly relevant in the fields of sensory materials and device engineering. As the subfield of MOF-based sensing has developed, many diverse chemical functionalities have been carefully and rationally implanted into the coordination nanospace of MOF materials. MOFs with widely varied fluorometric sensing properties have been developed using the design principles of crystal engineering and structure–property correlations, resulting in a large and rapidly growing body of literature. This work has led to advancements in a number of crucial sensing domains, including biomolecules, environmental toxins, explosives, ionic species, and many others. Furthermore, new classes of MOF sensory materials utilizing advanced signal transduction by devices based on MOF photonic crystals and thin films have been developed. This comprehensive review summarizes the topical developments in the field of luminescent MOF and MOF-based photonic crystals/thin film sensory materials. [ABSTRACT FROM AUTHOR]

A pure aqueous phase recognition and corresponding detoxification of highly toxic cyanide ions has been achieved by a fluorescent metal–organic framework (MOF). The cyanide detoxification has been shown to be effective even in in vitro studies and the MOF could be recycled to show the same efficiency of detoxification. [ABSTRACT FROM AUTHOR]

A chemically stable cationic MOF encapsulating an in situ formed water-hydroxide supramolecular anionic chain is realized for high hydroxide (OH−) ion conductivity in the solid-state (Type A). High OH− ion conductivity and low activation energy of the MOF demonstrate the advantage of the in situ incorporation of OH− ions to achieve efficient OH− ion conduction in the solid-state. [ABSTRACT FROM AUTHOR]

π-Complexation triggered Lewis acid–base interactions between open metal sites (OMS) of metal–organic frameworks (MOFs), and π-e− rich adsorptive benzene (Bz) is exploited to establish M-MOF-74 as the best Bz-selective MOF sorbent, marking the first report of utilizing OMS behind benzene/cyclohexane separation; a key advance from the energy-economy standpoint of industrial separation. [ABSTRACT FROM AUTHOR]

2,4,6-Trinitrophenol (TNP) is a highly explosive molecule that is also widely used in industrial processing on a large scale. During synthesis, processing and disposal, TNP is released to the environment especially to water streams, contaminating ground and surface water. TNP and its biologically transformed products like picramic acids have been identified as highly toxic species to biota and may lead to chronic diseases such as sycosis and cancer. Thus, aqueous phase detection of TNP becomes an imperative aspect for the design of any potential sensor. Metal–organic frameworks (MOFs) have emerged as an important class of sensors owing to their permanent porosity, designability and variety of signal transduction pathways. Luminescent MOFs (LMOFs) have shown great potential as sensors for various nitro explosives by modulation of their luminescence behaviour in the presence of nitro explosives. Most of the LMOFs detect nitro explosives in the vapour phase and/or in organic solvents while aqueous phase detection is rarely investigated. Herein we present recent developments in the area of LMOFs for aqueous phase TNP sensing and discuss strategies used to improve the sensing performance. Finally, based on our perspective, important aspects of LMOF performance needing immediate attention for future developments are provided. [ABSTRACT FROM AUTHOR]

This short review gives a focussed discussion on metal–organic frameworks (MOFs) made of neutral N-donor ligands which show structural flexibility under various exogenous stimuli. Chemical stimuli such as presence of anions, free guests, coordinated guests and physical stimuli (light, heat and so on) render structural flexibility in MOFs. Single-crystal-to-single-crystal transformation studies have attracted a lot of attention for the understanding of such flexible MOF materials. Such a dynamic structural behavior with proper host–guest interactions gives very interesting functions such as chemical separation, sensing and magnetic properties and so on. [ABSTRACT FROM AUTHOR]

A three dimensional (3D) cationic Metal–Organic Framework (MOF) has been fabricated from a neutral N-donor ligand and Cd(ClO4)2. The cationic MOF shows guest triggered inherent dynamic behaviour at room temperature. A single-crystal-to-single-crystal (SCSC) transformation experiment enabled the guest dependent structural dynamism to be well understood. The framework also displays facile anion exchange behaviour and anion dependent structural dynamism. [ABSTRACT FROM AUTHOR]

A diaminotriazine functionalized novel MOF (DAT-MOF-1) has been synthesized stemming out of a π-electron-deficient pore-surface functionalization based linker-design principle, which results in efficient selectivity of benzene sorption over its aliphatic analogue cyclohexane, crucial from the industrial standpoint. [ABSTRACT FROM AUTHOR]

Prompt and selective detection of nitro explosives in the aqueous phase is in high demand to meet homeland security and environmental concerns. Herein we report the chemically stable porous metal organic framework UiO-68@NH2 with a pendant recognition site for selective detection of the nitro-aromatic explosive TNP in the aqueous phase. The pendant Lewis basic amine moieties are expected to selectively interact with TNP via electrostatic interactions and act as recognition sites for TNP. The MOF can detect the presence of TNP in water at a concentration as low as 0.4 ppm with a response time of a few seconds. In addition, both excitation and emission wavelengths of the MOF are in the visible region. The high selectivity was observed even in the presence of competing nitro analytes in the aqueous phase. The quenching constant for TNP was found to be 5.8 × 104 M−1 which is 23 times higher than that for TNT and for RDX, demonstrating superior and selective quenching ability. This unprecedented selectivity is ascribed to electron-transfer and energy-transfer mechanisms as well as electrostatic interactions between TNP and the MOF. An MOF-coated paper strip that we prepared demonstrated fast and selective response to TNP in water, which represents a first step towards a practical application. [ABSTRACT FROM AUTHOR]

Selective and sensitive aqueous phase nitric oxide (NO) detection has been demonstrated by implementing an unsophisticated approach of ligand modulation in a porous, robust metal–organic framework (MOF). The detection is achieved through deamination by NO in an amine-decorated luminescent MOF. This is the first report of employing a physiologically stable, functionalized MOF as a NO sensor. [ABSTRACT FROM AUTHOR]

Selective and sensitive nitro explosive detection by a porous luminescent metal-organic framework has been reported. For the first time MOF based selective explosive detection in the presence of other nitro analytes in aqueous media is demonstrated. [ABSTRACT FROM AUTHOR]

Solid state supramolecular assembly of a novel C3-symmetric tripodal luminescent organic molecule has been explored to understand the molecular aggregation and the different possible interactions between host--host and host--guest pairs. Interesting capsule voided confinement of guest molecules and the helical arrangement via non-covalent interactions have been evidenced by single crystal X-ray diffraction and solid state circular dichroism study, respectively. Visual color change and variable temperature powder X-ray diffraction study supported solid state transitions in the supramolecular architecture. [ABSTRACT FROM AUTHOR]

A new three-dimensional (3D) bi-porous metal–organic framework (MOF), {[(Me2NH2)2]·[Cd3(5-tbip)4]·2DMF}n (1) (5-tbipH2: 5-tert-butylisophthalic acid) has been synthesized. The 5-tbip ligand containing a hydrophobic t-butyl group and hydrophilic carboxylate groups is used to synthesize the bi-porous framework. This 3D MOF contains two types of channels, a wide mouth hydrophilic channel of dimension 7.448 × 7.676 Å2 and a narrow mouth hydrophobic channel of dimension 2.33 × 1.926 Å2. Hydrophilic channels are lined with the orderly arranged dimethyl ammonium (DMA) cations which neutralize the anionic 3D framework. The guest-free form of the MOF (1′) showed interesting CO2 selectivity over other gases such as N2, CH4, and H2. Since the effective pore size of the desolvated compound 1′ (∼0.6 nm: from the pore size distribution curve of CO2 adsorption measurement) is much more than the kinetic diameter of all measured gases (CO2 = 3.3 Å, CH4 = 3.76 Å, N2 = 3.64 Å and H2 = 2.8 Å), selective capture of CO2 by 1′ could be ascribed to the strong electrostatic interaction of CO2 with the framework. Compound 1′ also shows reversible iodine uptake (1′⊂ 4I2: based on the sample weight measurements and TGA data) with visible color change of the compound. Interestingly, the iodine-loaded MOF showed ∼76 times increase in electrical conductivity compared to 1′. [ABSTRACT FROM AUTHOR]

Pyridine-2,4,6-tricarboxylic aci d (ptcH3) reacts with Cd(II), Mn(II), Ni(II), Mg(II), Ca(II), Sr(II), Ba(II), Dy(III) salts forming different products depending on the reaction conditions. In the presence of pyridine at room temperature the acetate, chloride or nitrate salt of Cd(II) breaks the ligand to form an open framework structure with the empirical formula, {[Cd(Ox)(H2O)2]H2O}n (Ox = oxalate), 1. In the absence of pyridine, no crystalline compound could be isolated at room temperature (RT). However, under hydrothermal conditions and in the absence of pyridine, a discrete tetrameric complex with the formula, {[Cd2(cda)2(H2O)4](H2O)3}2 (cdaH2 = 4-hydroxypyridine-2,6-dicarboxylic acid), 2, is formed where the carboxylate group at the 4-position of the ligand is reduced to a hydroxyl group.When Ni(II), Mn(II), Mg(II), Ca(II), Sr(II), Ba(II), Dy(III) salts are used in place of Cd(II), no crystalline product could be isolated at RT. But under hydrothermal conditions, coordination polymers ({[Ni1.5(ptc)(pip)0.5(H2O)4]·H2O}n, (pip = piperazine), 3; {Mn1.5(ptc)·2H2O}n, 4; {Mg3(ptc)28H2O}n, 5; {[Mg(ptc)(H2O)2]·1/2[Mg(H2O)6]·H2O}n, 6; {Ca1.5(ptc).2H2O}n, 7; {Sr1.5(ptc).5H2O}n, 8; {[Ba(ptc)(H2O)][Ba(ptcH2)H2O]}n, 9; {[Dy(ptc)·3H2O]·H2O}n, 10) are formed. The structures exhibit different dimensionality depending on the nature of the metal ions. In 1 a discrete acyclic water hexamer is also identified. All the compounds are characterized in the solid state by X-ray crystallography, IR and elemental analysis. [ABSTRACT FROM AUTHOR]

Effective sequestration of bromine holds great promise for the chemical industry's safe expansion, environmental preservation, and public health. However, attaining this goal is still challenging due to the serious drawbacks of existing adsorbents such as limited capacity, low retention efficiency, and sluggish uptake kinetics. Herein, we report a strategy-driven systematic study aimed at significantly enhancing multiple host-guest interactions to obtain functionalized covalent-organic frameworks for the efficient sequestration of bromine. Results showed that the presence of specific quantities of selective binding sites of the porous frameworks afford stronger host-guest interactions and therefore higher bromine adsorption capacities. The developed framework exhibits high bromine sorption capacity of up to 5.16 g g -1 in the vapor phase and 8.79 g g -1 in the aqueous phase under static adsorption conditions with fast kinetics, large distribution coefficient ( K d ∼10 5 mL g -1 ), high retention efficiency and reusability. Moreover, the adsorbent is able to sequestrate trace bromine (from 13 ppm to below 4 ppm) from aqueous medium with fast adsorption kinetics (86.3% within less than 3 h) and demonstrates the selective extraction of bromine over iodine under both static and dynamic conditions. These results were further utilized to demonstrate recycling-selective and highly efficient bromine capture from a real-water system, exhibiting excellent scalability and affordability, as exemplified using COF membranes in a continuous flow-through process.

99 Tc is one of the potentially toxic radioactive substances owing to its long half-life and a high degree of environmental mobility. Hence, the sequestration of 99 Tc from radioactive waste has become enormously important and a contemporary research priority. However, selective extraction of this species in its stable oxoanionic form ( 99 TcO 4 - ) is very challenging on account of bottlenecks such as low charge density, less hydrophilic nature, etc. Herein, an ultrathin hybrid composite material has been strategically designed and fabricated by covalent anchoring of a chemically stable amino functionalized nanosized cationic metal-organic polyhedron with a positively charged robust ionic covalent organic framework. The resulting thin-layer-based hybrid composite presented multiple exfoliated exposed interactive sites, including a Zr(iv)-secondary building unit, amine and triaminoguanidine functional groups, which can selectively interact with TcO 4 - oxoanions through a synergistic combination of electrostatic, H-bonding and various other supramolecular interactions. Thus synthesized function-tailored composite, by virtue of its multiple unique characteristics, manifested an ultrafast and very selective, high distribution coefficient (∼10 6 mL g -1 ), as well as recyclable entrapment of TcO 4 - oxoanions from the complex mixture of superfluous (∼5000-fold) other interfering anions in both high and ultra-trace concentrations along with simulated nuclear waste and from different water systems. Dynamic flow-through experiments were conducted with the membrane of the hybrid material in simulated wastewater, which reduced the concentration of ReO 4 - (surrogate of radioactive TcO 4 - ) to below the WHO permissible level with rapid sequestration kinetics and excellent selectivity over excessive competing anions., Competing Interests: The authors declare no competing interests., (This journal is © The Royal Society of Chemistry.)

Preferential trapping of a selected metal-oxoanion from a mixture of other metal-oxoanionic toxic pollutants in water has been demonstrated by implementing energy-efficient adsorption followed by the ion-exchange method, utilizing a hydrolytically stable cationic metal-organic framework (MOF). The cationic MOF exhibits ultrafast and selective extraction efficiency towards ReO 4 - (a surrogate anion of radioactive TcO 4 - ) over other metal-oxoanions in contaminated water systems.

Thanks to a bottom-up design of metals and organic ligands, the library of metal-organic frameworks (MOFs) has seen a conspicuous growth. Post-synthetically modified MOFs comprise a relatively smaller subset of this library. Whereas the approach of post-synthetic modification was seminally introduced for MOFs in the early 1990s, the earliest examples of post-synthetically modified MOFs are only congruous with adsorption and catalysis. The utility of PSM-derived MOFs for the sensing and capture of water contaminants is relatively niche. Arguably though, an increasing number of post-synthetically modified MOFs are finding relevance in the context of water pollutant remediation. In this article, we review the recent advances in this area and propose a structure-function relationship-guided blueprint for the future outlook.

Water pollution from heavy metals and their toxic oxo-anionic derivatives such as CrO42-, Cr2O72-, HAsO42-, and HAsO32- has become one of the most critical environmental issues. To address this, herein, we report a new hydrolytically stable luminescent Zn(ii) based cationic metal organic framework (MOF), iMOF-4C, which further successfully exhibited a rare dual "turn off/on" fluorescence response toward Cr(vi), As(v) and As(iii) based oxo-anions respectively in water medium. In addition, iMOF-4C was found to maintain its superior selectivity in the presence of other concurrent anions (e.g. SO42-, Cl-, Br-, ClO4-, NO3-, SCN- and CO32-). More importantly, iMOF-4C exhibited an excellent selective and sensitive luminescence "turn-off" response towards CrO42- and Cr2O72- anions in water medium with the quenching constant (Ksv) values as high as 1.31 × 105 M-1 (CrO42-) and 4.85 × 105 M-1 (Cr2O72-), which are found to be the highest among the values reported in the regime of MOFs. Interestingly, iMOF-4C showed fluorescence "turn-on" response toward HAsO42- and HAsO32- with an enhancement coefficient (Kec) of 1.98 × 104 M-1 and 3.56 × 103 M-1 respectively. The high sensitivity and low detection limits make iMOF-4C more feasible for real-time sensing of such toxic oxo-anions in an aqueous medium. Furthermore, the probable sensing mechanism has been investigated by DFT calculation studies and discussed in detail.

This short review gives a focussed discussion on metal-organic frameworks (MOFs) made of neutral N-donor ligands which show structural flexibility under various exogenous stimuli. Chemical stimuli such as presence of anions, free guests, coordinated guests and physical stimuli (light, heat and so on) render structural flexibility in MOFs. Single-crystal-to-single-crystal transformation studies have attracted a lot of attention for the understanding of such flexible MOF materials. Such a dynamic structural behavior with proper host-guest interactions gives very interesting functions such as chemical separation, sensing and magnetic properties and so on.

Prompt and selective detection of nitro explosives in the aqueous phase is in high demand to meet homeland security and environmental concerns. Herein we report the chemically stable porous metal organic framework UiO-68@NH2 with a pendant recognition site for selective detection of the nitro-aromatic explosive TNP in the aqueous phase. The pendant Lewis basic amine moieties are expected to selectively interact with TNP via electrostatic interactions and act as recognition sites for TNP. The MOF can detect the presence of TNP in water at a concentration as low as 0.4 ppm with a response time of a few seconds. In addition, both excitation and emission wavelengths of the MOF are in the visible region. The high selectivity was observed even in the presence of competing nitro analytes in the aqueous phase. The quenching constant for TNP was found to be 5.8 × 10(4) M(-1) which is 23 times higher than that for TNT and for RDX, demonstrating superior and selective quenching ability. This unprecedented selectivity is ascribed to electron-transfer and energy-transfer mechanisms as well as electrostatic interactions between TNP and the MOF. An MOF-coated paper strip that we prepared demonstrated fast and selective response to TNP in water, which represents a first step towards a practical application.

Herein, we present a carboxylate-based dinuclear dysprosium compound, namely [Dy(2)L(6)(MeOH)(2)(H(2)O)(2)] (LH = n-butyric acid) from the reaction of Dy(NO(3))(3)·xH(2)O with n-butyric acid and triethylamine in MeOH solvent. The single crystal X-ray diffraction analysis demonstrate that a total of six monocarboxylate ligands formed this dimeric compound by carboxylate bridging along with coordination from solvent molecules (water and methanol). Each Dy(III) ion is coordinated by nine donor atoms forming a mono-capped antiprismatic coordination environment. Alternating current (AC) magnetic measurements show a frequency dependence of the out-of-phase magnetic susceptibilities (χ'') indicating a slow relaxation behaviour of the magnetization.

The structural study of halide complexes has been performed on two laterally non-symmetric aza-oxa cryptands Lo and Lm having different cavity dimensions. For the fluoride complex of Lo, the 'oxa' end bridgehead N atom gets protonated to pull the internal fluoride towards the 'oxa' end. While bromide remains outside the cavity either by being sandwiched between the opposite-side directed arms of the two different moieties or by being incorporated into the space provided by the two same-side directed arms of a single Lo. In comparison, Lm having a higher cavity dimension can accommodate chloride and bromide in addition to fluoride in its cavity. While Lo changes its conformation for its bromide complex attaining a 'Y'-shaped architecture, cryptand Lm retains its symmetrical pinwheel shape viewed down the C(3) axis joining the two bridgehead amines throughout all of its halide complexes. While encapsulated fluoride resides at the 'oxa' end of Lo, the encapsulated fluoride/chloride/bromide of Lm is displaced far away from the 'oxa' end to the 'aza' end. However, iodide remains outside the cavity for both cryptands. Two discrete water heptamers of acyclic and cyclic/acyclic configurations have been characterised by X-ray diffraction. Discrete water trimer, tetramer and adamantanoid clusters have also been identified within these organic crystal hosts.