Santanu Chand

Structural variation of transition metal coordination polymers based on bent carboxylate and flexible spacer ligand: polymorphism, gas adsorption and SC-SC transmetallation

Reaction of the bent dicarboxylate ligand H2OBA (H2OBA = 4,4′-oxybisbenzoic acid) and the flexible linker 1,4-bis(3-pyridyl)-2,3-diaza-1,3-butadiene (L1), under diverse reaction conditions, forms two polymorphic Co(II) coordination polymers (CPs): {[Co(OBA)(L1)]·DMF}n (1), as a three dimensional (3D) framework with a pcu alpha-Po primitive cubic topology, and {[Co(OBA)(L1)]·DMF}n, (2), as a two dimensional (2D) structure with a 6-c uninodal net topology. Gas adsorption measurements of the desolvated Co(II) CPs show negligible uptake of all gases in 1, while 2 exhibits moderate uptake of CO2, with good selectivity over N2 and CH4. With Zn(II), reaction of H2OBA and L1 produces a different 2D CP, {[Zn0.5(OBA)0.5(L1)0.5]}n (3). Finally, three isostructural Cd(II) CPs, {[Cd(OBA)(L1)]·DMF}n (4), {[Cd(OBA)(L1)]·DEF}n (5), and {[Cd(OBA)(L1)]·DMA}n (6) (DMF = N,N-dimethylformamide, DEF = N,N-diethylformamide, DMA = N,N-dimethylacetamide), that differ only in the lattice solvent molecules and show 2D structural arrangements are prepared. Interestingly, CP 4 undergoes single-crystal to single-crystal (SC-SC) transmetallation reaction at room temperature, yielding isostructural {[Cu(OBA)(L1)]·DMF}n (7) that cannot be synthesized independently. Moreover, the luminescence properties of compounds 1, 2, 3, and 4 have been studied in the solid state at room temperature. All the complexes are characterized by elemental analysis, IR, TGA, PXRD and single crystal X-ray diffraction.

A Water-Stable Twofold Interpenetrating Microporous MOF for Selective CO2 Adsorption and Separation

Self-assembly of bent dicarboxylate linker 4,4-sulfonyldibenzoic acid (H2SDB) and flexible N,N-donor spacer 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene (L) with Co(NO3)2·6H2O forms a twofold interpenetrated {[Co2(SDB)2(L)]·(H2O)4·(DMF)}n, (IITKGP-6) network via solvothermal synthesis with sql(2,6L1) topology, which is characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, elemental analysis, powder X-ray diffraction (XRD), and single-crystal XRD. The framework is microporous with a solvent-accessible volume of 25.5% and forms a one-dimensional channel along [1-1 0] direction with the dimensions of ∼3.4 × 5.0 Å2. As the stability of metal-organic frameworks (MOFs) in the presence of water is a topic of significant importance while considering them for practical applications, this framework reveals its high stability toward water. The desolvated framework shows modest uptake of CO2 (50.6 and 37.4 cm3 g-1 at 273 and 295 K under 1 bar pressure, respectively), with high selectivity over N2 and CH4. Ideal adsorbed solution theory calculations show that the selectivity values of CO2/N2 (15:85) are 51.3 at 273 K and 42.8 at 295 K, whereas CO2/CH4 (50:50) selectivity values are 36 at 273 K and 5.1 at 295 K under 100 kPa. The high CO2 separation selectivity over N2 and CH4 along with its water stability makes this MOF a potential candidate for CO2 separation from flue gas mixture and landfill gas mixture as well.

A Moisture-Stable 3D Microporous CoII-Metal-Organic Framework with Potential for Highly Selective CO2 Separation under Ambient Conditions

Selective adsorption and separation of CO2 from flue gas and landfill gas mixtures have drawn great attention in industry. Porous MOF materials are promising alternatives to achieve such separations; however, the stability in the presence of moisture must be taken into consideration. Herein, we have constructed a microporous metal-organic framework (MOF) {[Co(OBA)(L)0.5 ]⋅S}n (IITKGP-8), by employing a V-shaped organic linker with an azo-functionalized N,N spacer forming a 3D network with mab topology and 1D rhombus-shaped channels along the crystallographic b axis with a void volume of 34.2u2009%. The activated MOF reveals a moderate CO2 uptake capacity of 55.4 and 26.5u2005cm3 u2009g-1 at 273 and 295u2005K/1u2005bar, respectively, whereas it takes up a significantly lower amount of CH4 and N2 under similar conditions and thus exhibits its potential for highly selective sorption of CO2 with excellent IAST selectivity of CO2 /N2 (106 at 273u2005K and 43.7 at 295u2005K) and CO2 /CH4 (17.7 at 273u2005K and 17.1 at 295u2005K) under 1u2005bar. More importantly, this MOF exhibits excellent moisture stability as assessed through PXRD experiments coupled with surface area analysis.

Polycarboxylate‐Templated Coordination Polymers: Role of Templates for Superprotonic Conductivities of up to 10−1 S cm−1

Three coordination polymers (CPs) have been synthesized based on a [Co(bpy)(H2 O)4 ]2+ chain (bpy=4,4-bipyridine) by a template approach. The frameworks are neutralized by different templated polycarboxylate anions (furan di-carboxylate (fdc) in Co-fdc, benzene tri-carboxylate (btc) in Co-tri and benzene tetra-carboxylate (btec) in Co-tetra). These templates with different degrees of protonation and ionic carrier concentration played significant role on crystal packing as well as formation of well-directed H-bonded networks which made these CPs perform well in proton conduction (PC). The PC value reaches to 1.49×10-1 u2005Su2009cm-1 under 80u2009°C and 98u2009% relative humidity (R.H.) for Co-tri, which is the highest among CPs/MOFs/COFs and is an example of conductivity in the order of 10-1 u2005Su2009cm-1 . Co-tri and Co-tetra are excellent proton conductors at mild temperature (40u2009°C) and 98u2009% R.H. (conductivities up to 2.92×10-2 and 1.38×10-2 u2005Su2009cm-1 , respectively).

Two azo-functionalized luminescent 3D Cd(II) MOFs for highly selective detection of Fe3+ and Al3+

Two cadmium-based 3D luminescent MOFs {[Cd2(SA)2(L)2]·H2O}n (Cd-MOF-1) and [Cd(CDC)(L)]n (Cd-MOF-2) (H2SA = succinic acid, H2CDC = 1,4-cyclohexanedicarboxylic acid, L = [3,3′-azobis(pyridine)]) have been assembled by employing organic dicarboxylic acid linkers with an unexploited azo-functionalized N,N′ spacer via a room temperature slow evaporation process, and they are characterized by single crystal X-ray analysis, TGA, FT-IR, PXRD and elemental analysis. The topological analysis reveals that Cd-MOF-1 features a 6c-uninodal rare ‘rob’ topology with the point symbol {48·66·8}, whereas Cd-MOF-2 shows a ‘pcu’ alpha-Po primitive cubic topology with the point symbol {412·63}. These MOFs are highly emissive at 382 nm and 398 nm when excited at 305 nm and 312 nm, respectively. The exposed azo groups are presumed to act as functional sites for the recognition of metal ions through quenching of fluorescence intensity. The fluorescence measurements show that these MOFs can selectively and sensitively detect Fe3+ as well as Al3+ and thus, they demonstrate potential as dual-responsive luminescent probes for metal-ion sensing. EDS elemental mapping, PXRD of loaded MOF materials, and a plausible quenching mechanism have been discussed. More importantly, both the MOFs exhibit rapid response times toward sensing of Fe3+ and Al3+.