Water adsorption in porous materials is important for many applications such as dehumidification, thermal batteries, and delivery of drinking water in remote areas. In this study, we have identified three criteria for achieving high performing porous materials for water adsorption. These criteria deal with condensation pressure of water in the pores, uptake capacity, and recyclability and water stability of the material. In search of an excellently performing porous material, we have studied and compared the water adsorption properties of 23 materials, 20 of which are metal–organic frameworks (MOFs). Among the MOFs are 10 zirconium(IV) MOFs with a subset of these, MOF-801-SC (single crystal form), −802, −805, −806, −808, −812, and −841 reported for the first time. MOF-801-P (microcrystalline powder form) was reported earlier and studied here for its water adsorption properties. MOF-812 was only made and structurally characterized but not examined for water adsorption because it is a byproduct of MOF-841 s...

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Water Adsorption in Porous Metal–Organic Frameworks and Related Materials

A self-consistent system of additive covalent radii, R(AB)=r(A) + r(B), is set up for the entire periodic table, Groups 1-18, Z=1-118. The primary bond lengths, R, are taken from experimental or theoretical data corresponding to chosen group valencies. All r(E) values are obtained from the same fit. Both E-E, E-H, and E-CH 3 data are incorporated for most elements, E. Many E-E' data inside the same group are included. For the late main groups, the system is close to that of Pauling. For other elements it is close to the methyl-based one of Suresh and Koga [J. Phys. Chem. A 2001, 105, 5940] and its predecessors. For the diatomic alkalis MM' and halides XX', separate fits give a very high accuracy. These primary data are then absorbed with the rest. The most notable exclusion are the transition-metal halides and chalcogenides which are regarded as partial multiple bonds. Other anomalies include H 2 and F 2 . The standard deviation for the 410 included data points is 2.8 pm.

Molecular single-bond covalent radii for elements 1-118.

Noncovalent interactions: a challenge for experiment and theory

Water is of fundamental importance for human life and plays an important role in many biological and chemical systems. Although water is the most abundant compound on earth, it is definitely not a simple liquid. It possesses strongly polar hydrogen bonds which are responsible for a striking set of anomalous physical and chemical properties. For more than a century the combined importance and peculiarity of water inspired scientists to construct conceptual models, which in themselves reproduce the observed behavior of the liquid. The exploration of structural and binding properties of small water complexes provides a key for understanding bulk water in its liquid and solid phase and for understanding solvation phenomena. Modern ab initio quantum chemistry methods and high-resolution spectroscopy methods have been extremely successful in describing such structures. Cluster models for liquid water try to mimic the transition from these clusters to bulk water. The important question is: What cluster properties are required to describe liquid-phase behavior?

Water: From Clusters to the Bulk

Molecular Clusters of π-Systems: Theoretical Studies of Structures, Spectra, and Origin of Interaction Energies

Resonant two-photon ionization, ultraviolet hole-burning, and resonant ion-dip infrared (RIDIR) spectroscopy were used to assign and characterize the hydrogen-bonding topology of two conformers of the benzene-(water) 8 cluster. In both clusters, the eight water molecules form a hydrogen-bonded cube to which benzene is surface-attached. Comparison of the RIDIR spectra with density functional theory calculations is used to assign the two (water) 8 structures in benzene-(water) 8 as cubic octamers of D 2 d and S 4 symmetry, which differ in the configuration of the hydrogen bonds within the cube. OH stretch vibrational fundamentals near 3550 wave numbers provide unique spectral signatures for these “molecular ice cubes.”

https://science.sciencemag.org/content/sci/276/5319/1678.full.pdf

Infrared Spectrum of a Molecular Ice Cube: The S4 and D2d Water Octamers in Benzene-(Water)8

Resonant two‐photon ionization spectroscopy was used to study jet‐cooled Ni2 produced by pulsed laser ablation of a nickel target in the throat of a supersonic nozzle using argon as the carrier gas. Spectral regions previously investigated using helium as the carrier gas were reinvestigated, and the improved cooling achieved was found to suppress transitions arising from an Ω=4 state that had been thought to be the ground state. Seven new vibronic progressions were assigned, with spectroscopic constants determined for the excited states. The predissociation threshold in Ni2 was reinvestigated, and a revised value for the binding energy is given as D○0(Ni2)=2.042±0.002 eV. The ionization energy of Ni2 was found to be 7.430±0.025 eV, and from this result and the revised bond dissociation energy of the neutral, the binding energy of the cation was calculated to be D○0(Ni+2)=2.245±0.025 eV. Similarly, D○0(Ni−2)=1.812±0.014 eV is obtained using D○0(Ni2) and the electron affinities of Ni and Ni2. Twenty bands w...

Ni2 revisited: Reassignment of the ground electronic state

The techniques of resonant two-photon ionization (R2PI), UV–UV (ultraviolet) hole-burning, and resonant ion-dip infrared (RIDIR) spectroscopies have been employed along with density functional theory (DFT) calculations to assign and characterize the hydrogen-bonding topologies of two isomers each of the benzene-(water)8 and (benzene)2(water)8 gas-phase clusters The BW8 isomers (B=benzene, W=water) have R2PI spectra which are nearly identical to one another, but shifted by about 5 cm−1 from one another This difference is sufficient to enable interference-free RIDIR spectra to be recorded As with smaller BWn clusters, the BW8 clusters fragment following photoionization by loss of either one or two water molecules The OH stretch IR spectra of the two BW8 isomers bear a close resemblance to one another, but differ most noticeably in the double-donor OH stretch transitions near 3550 cm−1 Comparison to DFT calculated minimum energy structures, vibrational frequencies, and infrared intensities leads to an assignment of the H-bonding topology of the BW8 isomers as nominally cubic water octamers of S4 and D2d symmetry surface attached to benzene through a π H-bond A series of arguments based on the R2PI and hole-burning spectra leads to an assignment of additional features in the R2PI spectra to two isomers of B2W8 The OH stretch RIDIR spectra of these isomers show them to be the corresponding S4 and D2d analogs of B2W8 in which the benzene molecules each form a π H-bond with a different dangling OH group on the W8 sub-cluster

Resonant ion-dip infrared spectroscopy of the S4 and D2d water octamers in benzene-(water)8 and benzene2-(water)8

The observation of an abrupt predissociation threshold in an extremely congested electronic spectrum has been used to measure the bond dissociation energies of the mixed early-late transition metal molecules YCo, YNi, ZrCo, ZrNi, NbCo, and NbNi. In these systems it is argued that predissociation occurs as soon as the ground separated atom limit is exceeded, providing values of Di(YCo) = 2.591 f 0.001 eV, Di(YNi) = 2.904 f 0.001 eV, D:(ZrCo) = 3.137 f 0.001 eV, Di(ZrNi) = 2.861 f 0.001 eV, Di(NbCo) = 2.729 f 0.001 eV, and Di(NbNi) = 2.780 f 0.001 eV. In addition, the bond strength of diatomic zirconium has been measured as Di(Zr,) = 3.052 f 0.001 eV. A discussion of the chemical bonding in the mixed early-late transition metal dimers and Zr1 is presented, based on the measured bond energies of these species. I. Introduction The chemical bonding between transition metal atoms is an area of interest to many different branches of chemistry, including metallurgy, surface science, and metal cluster chemistry. Unraveling the details of the complicated electronic structure in these metallic species is an ongoing process pursued through both experimental1.2 and theoreticaP4 avenues. From this research it is already clear that several distinct factors combine to determine thestrength and character of the chemical bond between transition metal atoms. One such factor is the loss of exchange energy which occurs upon formation of d-electron bonds, thereby reducing the strength of the chemical bonding. This is illustrated in the example of Ti2,5 where exchange effects favor the 4sui3d~:3du:3d6:, 3As,, state as a candidate for the ground state, while bonding considerations favor the 4sui3d?r~3du~, IZ; state. In Ti2 the balance between exchange effects and chemical bonding is so delicate that ab initio theory is incapable of determining which possibility is the ground state.5 Experimentally it is found that exchange effects dominate in Tiz, leading to an X 3$,, ground state.6 In the isovalent Zr2 molecule, however, the larger d-orbitals favor bond formation, leading to a strong theoretical prediction of a '2: ground Thus, to understand the bonding in the diatomic transition metals the competing effects of exchange and chemical bonding must be carefully considered.

http://chem.utah.edu/_documents/faculty/morse/69.pdf

Bond Strengths of Transition Metal Diatomics: Zr2, YCo, YNi, ZrCo, ZrNi, NbCo, and NbNi

A band of jet‐cooled 48Ti2 has been located in the near infrared by resonant two‐photon ionization spectroscopy. Rotational analysis has shown the band to be an Ω’=0±←Ω‘=1 transition, which is consistent with the 3Δg ground state proposed by Bauschlicher et al. [J. Chem. Phys. 95, 1057 (1991)]. The band is assigned as a 3Π0u ← X 3Δ1g transition, and lower and upper state bond lengths have been determined as r0(X 3Δg)=1.9422±0.0008 A and r0(3Πu)=1.997±0.009 A (1σ error limits, corrected for spin–uncoupling effects). Comparisons are made to the TiV and V2 molecules, a rationale for the unusual filling order of the 3d‐based molecular orbitals is provided, and molecular orbital assignments are considered for the excited 3Πu state.

Caleb A. Arrington

Papers

Infrared Spectrum of a Molecular Ice Cube: The S4 and D2d Water Octamers in Benzene-(Water)8

Ni2 revisited: Reassignment of the ground electronic state

Resonant ion-dip infrared spectroscopy of the S4 and D2d water octamers in benzene-(water)8 and benzene2-(water)8

Bond Strengths of Transition Metal Diatomics: Zr2, YCo, YNi, ZrCo, ZrNi, NbCo, and NbNi

The 3Π0u ← X 3Δ1g band system of jet‐cooled Ti2