1D02
Triptycene derivative based Metal-Organic Frameworks: UnusualTopologies and Electronic Properties○Zhongyue Zhang1, Kunio Awaga2,
1
Department of Chemistry, Research Center for Materials Science, Nagoya University, Japan2
Department of Chemistry and Integrated Research Consortium on Chemical Sciences,
Nagoya University, Japan[Abstract]
Research of two-dimensional (2D) semiconductive metal-organic frameworks (MOFs) has
been an attractive topic for coordination chemists and material scientists, as these materials
intrinsically and perfectly combine two important features: porosity and conductivity together
within a sole material. Hence, various applications, such as electrocatalysis, FET devices,chemiresistive sensors and supercapacitors have be pursued for these materials. However,with a rigid planar structure, triphenylene derivative ligands tend to create two-dimensional
layered graphene analogue structures with strong π-π interactions and leave little space forchemists to introduce any manipulation. To create some MOFs with potential electric andmagnetic properties, herein we introduce a new series of ligands: triptycene derivatives andMOFs based on these ligands. Similar to the triphenylene ligands, triptycene derivatives get
spontaneously oxidized and form a triradical linkage in the scaffolds, in contrast, absence ofstrong intermolecular π-π interactions has resulted 3-D MOF structures with rare topologies
and unprecedented connectivity.
[Introduction]
The study of topological insulators has become an extremely hot topic of condensed
matter physics, as these materials have unusual band structures like Dirac cones, and exotic
electronic properties. To date, most topological materials are solid-state semiconductors, like
Bi2Te3, and their band structure is determined by the topology of crystal structures. Very few
works have been concerning the construction of interesting topologies with molecule-basedmaterials. On the other hand, in the field of metal-organic frameworks (MOFs), people haveestablished a mature crystal engineering method to build porous coordination networks withdesired topologies, but no effort has even been performed to examine the physical properties
that arises from these topologies. This research intends to combine the crystal engineering
strategies with the study of topological materials, to develop a synthetic strategy of functional
MOFs with special topologies, such as Kagome and gyroid, and to understand the relationshipbetween the topologies of MOFs and their electronic and magnetic properties.
In practice, this research focuses on the preparation of triptycene derivative based
metal-organic frameworks (MOFs). The triptycene molecule has a rigid structure and a 3-foldaxis of rotation, therefore, combining with transition metals with different coordination
environment preferences, such as square planar, tetrahedral and octahedral, coordination
networks with various topologies, including Kagomélattices and gyroid structures. Triptycene
derivatives have a same feature: when forming a coordination polymer, the ligand will get
partially oxidized and form an organic radical with multiple spins. With the special topologyof these networks, interesting physical properties, such as high conductivity, molecularmagnetism, exotic band structures and Dirac cones, spin frustration and spin liquids may beobserved.

[Methods]
Preparation and characterization of the MOFs: To date, two ligands, hexahydroxy
triptycene (TripOH-H) and hexahydroxy 13,14-dimethytriptycene (TripOH-Me) wereprepared according to the literature methods. (Fig. 1) Metal-organic frameworks withtransition metals were prepared via hydrothermal methods and slow diffusion methods. In
these reactions, metal acetate complexes were used to deprotonate the triptycene ligands andthe ligands got spontaneously oxidized by air during the hydrothermal reactions and diffusion.
Crystals or crystalline powders were collected and subjected to single crystal XRD, PXRD,
SEM and TEM measurements to determine their structures and morphologies.

Fig. 1. Preparation of hexahydroxy triptycene derivative ligands.

[Results and Discussion]
Unlike the reported 2D semiconductive MOFs, by varying the metal cations and axial
R-groups of the ligand, structures with different topologies could be obtained. In the case of
Ni-TripOH-H, SEM image suggested a prism crystal with tetragonal unit cells. For
Ni-TripOH-Me, two phases could be found by manipulating the solvent and reaction time.
The single crystal of phase B was obtained, and the structure was determined. (Fig. 2) The
structure consists the triradical form of TripOH-Me bridging octahedral coordinated Ni(II)with two water molecules filling the coordination sphere. Two type of 1-D rectangularchannels are found, one with a dimension of 1.8nmⅹ1.2nm, and the other with a dimensionof 0.7ⅹ0.6nm. It is noteworthy that the 3-D structure is composed by interweaven ladders,which are not covalently bonded but connected with radical interactions. Therefore, chains ofcontinuouslyinteracting
radicals
areformed in thestructure, whichprovides
potential
electronconducting
pathways.
Fig. 2. Structure of Ni-TripOH-Me MOF and an illustration of radical chains in thestructure.

[References][1] B. Ghanem et al. Macromolecules 43, 5287 (2010).
[2] D. Sheberla et al. J. Am. Chem. Soc. 136, 8859(2014).