Dalton Transactions Blog

In a recent article from the group of Deanna D’Alessandro at the the University of Sydney, Australia, Liang et al. have shown for the first time a 3D metal-organic framework (MOF) comprised solely of the monocarboxylate ligand derived from formic acid, with exceptionally selective CO₂ adsorption properties.

For those involved in MOF chemistry, it is well accepted that in most cases, organic bridging ligands should have at least two coordinating functional groups that link adjacent inorganic secondary building units into a porous crystalline lattice. Therefore, it comes as a complete surprise to find that a porous MOF can be formed entirely of monocarboxylate ligands that are traditionally used to cap and thus prevent further growth of the framework. Through structural characterisation, Liang et al. have shown that the formate takes on two different binding modes within the framework; one that caps the oxyzirconium cluster secondary building units, and another that bridges and interconnects these into a crystalline architecture.

Why is this important, I hear you ask? As the formate ligands are very small, this results in the formation of very small pores that can lead to selectivity in the adsorption of different gases. This is just what has been shown by Liang et al., with adsorption isotherms demonstrating that adsorption of CO₂ is a factor of 145 higher than for N₂. Potential applications may lead to the sequestration and use of greenhouses gases such as CO₂ from the atmosphere.

Check out the full article now!

The first example of a zirconium-oxide based metal–organic framework constructed from monocarboxylate ligands
Weibin Liang, Ravichandar Babarao, Michael J. Murphya and Deanna M. D’Alessandro
Dalton Trans., 2015, 44, 1516-1519

Christopher Hinde obtained his Masters degree in Chemistry from the University of Southampton, UK in 2011. He is currently doing research towards a Ph.D. in the area of materials chemistry and catalysis under the supervision of both Dr Robert Raja at the University of Southampton and Professor T. S. Andy Hor at the Institute of Materials Research and Engineering (IMRE), part of Singapore’s Agency for Science Technology and Research (A*STAR).

Yanfeng Yue and co-workers have developed a novel method for introducing mesoporosity into a series of metal–organic framework (MOF) materials by using “perturbation-assisted nanofusion”, as described in their recent Dalton Transactions paper. The authors exemplified the importance of their work by showing that large dye molecules can be encapsulated in the mesopores for luminescent sensing of volatile organic compounds (see also the image below, from Yue and co-workers).

Introducing mesoporosity into microporous frameworks has been of interest to materials chemists for several years, in an effort to expand the functionality and widen the potential applications of nanoporous materials.

Microporous materials have proved to be great tools for achieving precision in catalysis, separations and sensing (among others), by using internal surfaces or porosity in a multitude of ways. However, by introducing mesoporosity, one can overcome certain limitations, such as diffusion or small molecule selectivity, and one can even introduce multifunctionality by using the properties of both the micropores and the mesopores within a structure.

Typical procedures for the fabrication of mesopores in MOF structures involve the use of wasteful techniques such as etching or organic templates. However, rather than building mesopores into single crystals of MOFs, Yue and co-workers take a different approach by constructing mesopores from fused MOF nanocrystals that are formed through a highly agitated synthesis procedure (that is, perturbation-assisted nanofusion). The result is the formation of a robust hierarchical superstructure through an inexpensive and economical process.

This out-of-the-box thinking allows the authors to exploit their new ‘bottom-up’ approach to introduce functional mesoporosity into MOF materials, for the sensing of volatile organic compounds.

It is easy to see how this method would be useful to researchers not only in sensing but also in any of the myriad established and emerging MOF applications.

Read the full article now at:

Encapsulation of large dye molecules in hierarchically superstructured metal–organic frameworks
Yanfeng Yue, Andrew J. Binder, Ruijing Song, Yuanjing Cui, Jihua Chen, Dale K. Hensley and Sheng Dai
Dalton Trans., 2014, 43, 17893-17898

Christopher Hinde obtained his Masters degree in Chemistry from the University of Southampton, UK in 2011. He is currently doing research towards a Ph.D. in the area of materials chemistry and catalysis under the supervision of both Dr Robert Raja at the University of Southampton and Professor T. S. Andy Hor at the Institute of Materials Research and Engineering (IMRE), part of Singapore’s Agency for Science Technology and Research (A*STAR).

From early on, we are taught to look at linear mathematical relationships as dependent variables that are determined by the value of an independent variable.

The reason that I find the phenomenon of hysteresis fascinating is that it is the violation of the above concept. By definition, the value of a dependent variable showing hysteresis depends not only on the value of the independent variable but also on whether the independent variable has been increasing or decreasing before it arrives at the value at which a measurement is taken. The dependent variable has a ‘memory’ of its path.

Examples of hysteresis are rare on a molecular level. One of several fascinating aspects of the recent Dalton Transactions paper by Guy Jameson and colleagues is that the (temperature-dependent) magnetism exhibited by the authors’ Fe(III) spin-crossover (SCO) complex shows two hysteresis loops; an example from Jameson and colleagues is shown below.

In transition metal complexes where both high spin and low spin states are possible, SCO occurs when a complex switches from one spin state to the other. Unsurprisingly, this is temperature-dependent, hence the temperature dependence of the magnetism. Hysteresis in magnetic measurements of SCO compounds is known, but Jameson and colleagues report a number of rare properties for the Fe(III) compound that they investigate, [Fe(qsal-Br)₂]NO₃•2MeOH (where qsal-Br denotes the (N-8-quinolyl)-5-bromo-salicylaldimate ligand).

The vast majority of complexes in which SCO occurs exhibit the phenomenon in a single step — at a certain temperature, all of the molecules in a bulk sample will convert from one spin state to the other. This is only the fifth example of a mononuclear Fe(III) complex that shows full SCO that occurs in two or more discrete increments where symmetry is lost within the molecular structure. In the case of this Fe(III) complex, the temperature range over which some metal nuclei are high spin, and some are low spin (in this case 50% each), is the largest ever reported for a mixed spin-state Fe(III): that is, 96 K.

Here, both steps exhibit hysteresis. The spin-state transitions occur at different temperatures when the authors start with the complex at 300 K and cool it, versus when they warm the complex from 4 K.

Read the full article at:

Abrupt two-step and symmetry breaking spin crossover in an iron(III) complex: an exceptionally wide [LS–HS] plateau
David J. Harding, Wasinee Phonsri, Phimphaka Harding, Keith S. Murray, Boujemaa Moubaraki and Guy N. L. Jameson
Dalton Trans., 2015, DOI: 10.1039/C4DT03184A

Ian Mallov is currently a Ph.D. student in Professor Doug Stephan’s group at the University of Toronto. His research is focused on synthesizing new Lewis-acidic compounds active in Frustrated Lewis Pair chemistry. He grew up in Truro, Nova Scotia and graduated from Dalhousie University and the University of Ottawa, and worked in chemical analysis in industry for three years before returning to grad school.