Koya Prabhakara Rao

Design of Superhydrophobic Porous Coordination Polymers through the Introduction of External Surface Corrugation by the Use of an Aromatic Hydrocarbon Building Unit

We demonstrate a new approach to superhydrophobic porous coordination polymers by incorporating an anisotropic crystal morphology featuring a predominant surface that is highly corrugated and terminated by aromatic hydrocarbon moieties. The resulting low-energy surface provides particularly promising hydrophobic properties without the need for postsynthetic modifications or surface processing that would block the porosity of the framework. Consequently, hydrophobic organic molecules and water vapor are able to penetrate the surface and be densely accommodated within the pores, whereas bulk water is repelled as a result of the exterior surface corrugation derived from the aromatic surface groups. This study provides a new strategy for the design and development of superhydrophobic porous materials.

A Family of Rare Earth Porous Coordination Polymers with Different Flexibility for CO2/C2H4 and CO2/C2H6 Separation

A family of new porous coordination polymers (PCPs) were prepared by the reaction of an acylamide modified ligand (H3L) and RE(NO)3·xH2O (RE = Y, La, Ce, Nd, Eu, Tb, Dy, Ho, and Tm). PXRD and single-crystal X-ray analyses of them revealed that, besides the La PCP, all other rare earth members gave isomorphous structures. The two types of structural toplogies obtained, although similar, differ in their alignment of acylamide functional groups and structural flexibility. Adsorption experiments and in situ DRIFT spectra showed that rigid frameworks have the typical microporous behavior and poor selective capture of CO2 over C2H4 and C2H6; however, the unique La-PCP with structural flexibility and close-packed acylamide groups has a high selective capture of CO2 with respect to C2H6 or C2H4 at 273 K, especially at the ambient pressure area (0.1-1 bar).

Double protonation of 1,5-bis(triarylaminoethynyl)anthraquinone to form a paramagnetic pentacyclic dipyrylium salt.

Protonation-induced intramolecular cyclization reactions of new donor (D)-acceptor (A) and D-A-D conjugated molecules 1-triarylaminoethynylanthraquinone (1-AmAq) and 1,5-bis(triarylaminoethynyl)anthraquinone (1,5-Am(2)Aq), respectively, were achieved. The former undergoes monoprotonation with bis(trifluoromethanesulfone)imide acid (TFSIH) to give pyrylium salt [1-AmPyl]TFSI, whereas the latter undergoes a novel double proton cyclization reaction to yield 1,5-bis(triarylamino)dipyrylium salt [1,5-Am(2)Pyl(2)](TFSI)(2) with a new pentacyclic backbone. This divalent cationic salt can be reduced to give the neutral species 2,8-bis(triarylamino)benzo[de]isochromeno[1,8-gh]chromene ([1,5-Am(2)Pyl(2)](0)), which maintains the planar pentacyclic backbone. The obtained condensed-ring compounds show unique optical, electrochemical, and magnetic properties due to the extremely narrow HOMO-LUMO gap. In particular, the dication [1,5-Am(2)Pyl(2)](2+) shows paramagnetic behavior with two spins centered on two triarylamine moieties through valence tautomerization with the pentacyclic backbone.

Benzo[e]pyrene Skeleton Dipyrylium Dication with a Strong Donor–Acceptor–Donor Interaction, and Its Two-Electron Reduced Molecule

The donor-acceptor-donor (D-A-D) conjugated molecules 1,4-bis(diarylaminophenylethynyl)anthraquinone (1,4-Am(2)Aq) and 1,4-bis(ferrocenylethynyl)anthraquinone (1,4-Fc(2)Aq), undergo a double proton cyclization reaction with bis(trifluoromethanesulfone)imide acid (TFSIH) to yield 1,4-bis(diarylaminophenyl or ferrocenyl) dipyrylium salts [1,4-R(2)Pyl(2)](TFSI)(2) (R=Am or Fc) with novel planar pentacyclic structures similar to the aromatic benzo[e]pyrene-type skeleton. [1,4-Am(2)Pyl(2)](TFSI)(2) could be reduced to give the neutral molecule [1,4-Am(2)Pyl(2)](0), which is stable and maintains the benzo[e]pyrene-type skeleton. To the best of our knowledge, this is the first oxygen-atom-containing polycyclic aromatic hydrocarbon with 22 (4n+2) π-electrons. The obtained condensed-ring benzo[e]pyrene-type skeleton compounds show physical and chemical properties that are significantly different from those of [1,5-Am(2)Pyl(2)](TFSI)(2), which has a perylene-type skeleton.

A Dense I1O3 Hybrid Superhydrophobic Network, Pb(H-BTMB), Exhibits Selectivity toward CO2 Gas Sorption

We achieved a dense I1O3 hybrid superhydrophobic porous coordination polymer (PCP), [Pb(H-BTMB)(DMF)] (1), by solvothermal methods. The single-crystal XRD structure of 1 indicated that it has a three-dimensional M-L-M framework with one-dimensional M-O-M connectivity leading to an I1O3 network. The new PCP obtained exhibited open metal sites (OMSs) by losing a coordinated DMF molecule. The degassed phase displayed selective adsorption of CO2 gas over N2, C2H6, and C2H4 gases. Additionally, it has a superhydrophobic surface with a contact angle of 156.4° at room temperature and it is stable even at 90 °C, displaying a contact angle of 135.3°.

Temperature-Stable Compelled Composite Superhydrophobic Porous Coordination Polymers Achieved via an Unattainable de Novo Synthetic Method

We demonstrate a new de novo synthetic methodology to achieve high-temperature-stable compelled composite superhydrophobic porous coordination polymers (PCPs). These new PCPs were achieved based on coordination capabilities of first-row transition metal ions such as Co2+, Ni2+, and Zn2+. The obtained composite PCPs containing a [Zn2M2O]6+ (M = Co or Ni) bimetallic cluster core with open metal sites (OMSs) exhibited distinct isosteric heats of adsorption and surface areas due to the difference in their open metal Lewis acidic sites of solvent-free state. Additionally, these composite PCPs exhibit remarkable superhydrophobic properties with contact angles of 159.3° and 160.8° respectively for Zn-Co and Zn-Ni analogues. This superhydrophobic surface survives even at high temperature for longer time periods. As projected, these new composite PCPs exhibit better surface area and heats of adsorption compared to the PESD-1 (Zn) analogue due to a larger number of OMSs. Moreover, they display selective adsorption toward aromatic solvents such as benzene and toluene over aliphatic solvents such as cyclohexane due to corrugated and terminated aromatic hydrocarbon moieties toward the interactive surface. They also exhibit oil spill cleanup from the water surface in the powder form as well as pellet form up to 385 wt %. This study certainly offers a roadmap for designing and engineering new composite superhydrophobic porous materials for better water and thermal stability along with OMSs. This type of PCP exhibits a wide range of applications especially in catalysis, separation technology, and securing environmental problems such as oil spill cleanup in seawater.