Electrically Conducting Two-Dimensional Materials With Metal-Ortho-Phenylenediimine Units

Technology

This invention replaces conventional organic building blocks for MOFs with molecules containing ortho-diimine groups, which self-assemble, together with metals, into two-dimensional sheets resembling graphene. The square-planar metal-bis(phenylenediimine) connections established in these new materials, termed metal-organic graphene analogs (MOGs), lead to excellent charge delocalization across the MOF metal node and a considerable improvement in the materials’ electrical properties, making them more attractive for applications in the semiconductor and electronic device industry as well as in the electrical energy storage industry. These novel sMOGs are synthesized by reacting organic ligands containing at least two ortho-phenylenediamine groups with metal salts. The organic ligands are oxidized and each ortho-phenylenediamine group is transformed into an ortho-phenylenediimine group, which binds to the metal ion. Oxidation and formation of the ortho-diimine group is essential for electrical conductivity.The inventors have identified a compound, Ni(isq)2, as a target for the construction of a fully charged-delocalized s-MOG. Ni(isq)2 is fully π-conjugated with its ground state having partial singlet biradical character. The inventors perform a 2D extension of Ni(isq)2 ­­by reacting hexaaminotriphenylene hexahydrochloride (HATP 6HCl) with ammoniacal NiCl2 to produce a new crystalline s-MOG with very high electrical conductivity that is linearly proportion to its temperature. The conductivity of this new material vastly exceeds those of previous s-MOGs and other conductive MOFs and is higher than even some of the best organic conductors, rivaling graphite itself.  

Problem Addressed

MOFs and covalent-organic frameworks (COFs) present exceptional porosity and surface area, and are thus considered exceptional gas storage materials. However, their charge mobility and electrical conductivity have been very low, such that MOFs and COFs can effectively be categorized as insulators. The lack of electrical conductivity is due to the type of functionalities typically used to connect metals and organic ligands, which are not conducive to charge transport.  

Advantages    

• Method amenable to chemical functionalization, allowing for tunable electrical properties
• MOGs have similar electronic properties to graphene but offer greater compositional tunability
• MOGs using metal ortho-phenylenediimine groups offer improved electrical conductivity over those using other types of organic ligands