Pretty Structures

The tetrasilver complex [AgI(pmtbH)]₄ (where pmtbH is 2-[(2-pyridinylmethyl)thio]-1H-benzimidazole) forms as a surprisingly compact cluster in which:

• four Ag(1) ions (silver) form a central Ag₄ tetrahedron
• four iodide ions (purple), each cap a face of the tetrahedron
• four pmtbH ligands complete the coordination of the silver ions
• there are four weak S^.....I interactions
• intramolecular NH^.....N H-bonds satisfy the remaining bonding capacity
• the molecule has 4 point symmetry (it lies on a four-fold rotation-inversion axis)

A related polymeric complex, {[Ag₄(pmtbH)₄(NO₃)₄·2X}_n (X = solvent), shows antimicrobial activity in vitro; and stimulates the immune system of Galleria mellonella larvae in vivo. Preliminary mechanistic studies using flow cytometry suggest the antimicrobial response is linked to bacterial programmed cell death. The Ag₄ cluster is not biologically active but it is a much prettier structure.

Tetrameric and Polymeric Silver Complexes of the Omeprazole Scaffold; Synthesis, Structure, in vitro and in vivo Antimicrobial Activities and DNA Interaction. V. Jakobsen, L. Viganor, A. Blanco-Fernández, O. Howe, M. Devereux, C. J. McKenzie, and V. McKee. J. Inorg. Biochem., 2018, 168, 317-328.

The cluster Mg₂Ti₄(O)₂(OH)₄(CF₃COO)₈(THF)₆] is an example of a set of bimetallic complexes, all with challenging crystallographic disorder problems. I like them because I invested a lot of time in them.
The structure was refined in space group Pbca with a disorder about the centre of symmetry which was not reduced by reducing the symmetry of the system to Pca2₁ or P2₁2₁2₁. The core of the molecule consists of a tetrahedron of Ti(II) ions. Each edge of the tetrahedron is bridged by an oxygen atom, generating a Ti₄O₆ adamantane cage. Four of the bridging species are hydroxo ions; the remaining two are oxo ions which are also coordinated to Mg(II) ions.
The disorder arises from Ti ions occupying alternative sites (by inversion or 2-fold rotation), generating an overlapping adamantine with the oxygen atoms in the same positions. Four trifluoroacetate ions are bonded to each magnesium ion, each bridging to a titanium ion. All of the metal ions are six-coordinate, the last binding site being filled by one THF ligand for each metal ion.
Rather sadly, these neat molecules are designed and synthesised in order to be decomposed easily to form mixed-metal oxide layers for photoelectrochemical applications.

MgTi₂O₅, Thin Films from Single Molecular Precursor for Photoelectrochemical Water Splitting. M. A. Ehsan, R. Naeem, V. McKee, A. H. Saeed, and M. Mazhar. Solar Energy Materials and Solar Cells, 2017, 161, 328-337.

This one is only a movie, it is not interactive.
The movie shows a section of a MOF prepared from:

This structure was published in a special issue of Aust. J. Chem. in honour of Prof Richard Robson, a pioneer of MOF chemistry.

Reversible and Vapochromic Chemisorption of Ammonia by a Copper(II) Coordination Polymer.
C. Wegeberg, D. Nielsen, S. Mossin, B. F. Abrahams, V. McKee and C.J. McKenzie. Aust. J. Chem., 2019, 72, 817-826.