Michael C. Pfrunder

Atomic resolution of structural changes in elastic crystals of copper (II) acetylacetonate

Single crystals are typically brittle, inelastic materials. Such mechanical responses limit their use in practical applications, particularly in flexible electronics and optical devices. Here we describe single crystals of a well-known coordination compound-copper(II) acetylacetonate-that are flexible enough to be reversibly tied into a knot. Mechanical measurements indicate that the crystals exhibit an elasticity similar to that of soft materials such as nylon, and thus display properties normally associated with both hard and soft matter. Using microfocused synchrotron radiation, we mapped the changes in crystal structure that occur on bending, and determined the mechanism that allows this flexibility with atomic precision. We show that, under strain, the molecules in the crystal reversibly rotate, and thus reorganize to allow the mechanical compression and expansion required for elasticity and still maintain the integrity of the crystal structure.

Co-Crystallisation of 1,4-Diiodotetrafluorobenzene with Three Different Symmetric Dipyridylacetylacetone Isomers Produces Four Halogen-Bonded Architectures*

The co-crystallisation behaviour of three symmetrical dipyridylacetylacetone ligands (1,3-di(2-pyridyl)-1,3-propanedione (o-bppdH), 1,3-di(3-pyridyl)-1,3-propanedione (m-bppdH), and 1,3-di(4-pyridyl)-1,3-propanedione (p-bppdH)), with the linear halogen-bond donor 1,4-diiodotetrafluorobenzene (1,4-DITFB) has been investigated. The reaction of these components under ambient conditions in a 1 : 1 stoichiometry produced four halogen-bonded assemblies ([o-bppdH·1,4-DITFB, [m-bppdH·1,4-DITFB], [2(m-bppdH)·1,4-DITFB], and [p-bppdH·1,4-DITFB]). The combination of multiple supramolecular interactions including halogen bonding, hydrogen bonding, and π-stacking produces a range of supramolecular architectures, including one-, two-, and three-dimensional motifs. The crystal structure of m-bppdH is also reported.

A three-dimensional cubic halogen-bonded network

The rational, deliberate design of supramolecular architectures is of great importance for the discovery of complex materials. A three-dimensional cubic halogen-bonded network has been prepared by combination of an octahedral metal-containing halogen bond acceptor and a linear ditopic donor. This material displays α-Po pcu topology and is seven-fold interpenetrated. This is the first neutral, metal-containing three-dimensional halogen-bonded network to be reported.

Elastically Flexible Crystals have Disparate Mechanisms of Molecular Movement Induced by Strain and Heat

Elastically flexible crystals form an emerging class of materials that exhibit a range of notable properties. The mechanism of thermal expansion in flexible crystals of bis(acetylacetonato)copper(II) is compared with the mechanism of molecular motion induced by bending and it is demonstrated that the two mechanisms are distinct. Upon bending, individual molecules within the crystal structure reversibly rotate, while thermal expansion results predominantly in an increase in intermolecular separations with only minor changes to molecular orientation through rotation.

CCDC 1529014: Experimental Crystal Structure Determination

Related Article: Anna Worthy, Arnaud Grosjean, Michael C. Pfrunder, Yanan Xu, Cheng Yan, Grant Edwards, Jack K. Clegg, John C. McMurtrie|2017|Nature Chemistry|||doi:10.1038/nchem.2848

CCDC 1529012: Experimental Crystal Structure Determination

Related Article: Anna Worthy, Arnaud Grosjean, Michael C. Pfrunder, Yanan Xu, Cheng Yan, Grant Edwards, Jack K. Clegg, John C. McMurtrie|2017|Nature Chemistry|||doi:10.1038/nchem.2848

CCDC 1529021: Experimental Crystal Structure Determination

Related Article: Anna Worthy, Arnaud Grosjean, Michael C. Pfrunder, Yanan Xu, Cheng Yan, Grant Edwards, Jack K. Clegg, John C. McMurtrie|2017|Nature Chemistry|10|65|doi:10.1038/nchem.2848

CCDC 1529040: Experimental Crystal Structure Determination

Related Article: Anna Worthy, Arnaud Grosjean, Michael C. Pfrunder, Yanan Xu, Cheng Yan, Grant Edwards, Jack K. Clegg, John C. McMurtrie|2017|Nature Chemistry|10|65|doi:10.1038/nchem.2848

Chapter 10:Functional Metallo-supramolecular Polyhedral Capsules and Cages

Metallo-supramolecular capsules and cages epitomise the elegant manner in which self-assembled functional materials can be designed from first principles. Not only are these materials inherently beautiful, they are useful, performing myriad functions within the spaces that they enclose. Metallo-supramolecular capsules and cages can be prepared to be charged or neutral, large or small, open or closed and often display interesting properties including notable spectrochemical, electrochemical and magnetic effects in their own right. Through encapsulation, metallo-supramolecular capsules and cages have been demonstrated to be useful agents for host–guest chemistry, binding a wide variety of guests such as anions, cations or neutral molecules (including gases) and have been shown to catalyse a number of reactions producing unusual products more efficiently. In this chapter, after briefly discussing the design of these materials and the process of encapsulation, we survey the functions performed by metallo-supramolecular capsules and cages including selective guest binding, separations of molecular mixtures, sequestration of greenhouse gases and their use as modulators of chemical reactivity.