Single Crystals of Electrically Conductive Two-Dimensional Metal–Organic Frameworks: Structural and Electrical Transport Properties

Abstract

Crystalline, electrically conductive, and intrinsically porous materials are rare. Layered two-dimensional (2D) metal–organic frameworks (MOFs) break this trend. They are porous crystals that exhibit high electrical conductivity and are novel platforms for studying fundamentals of electricity and magnetism in two dimensions. Despite demonstrated applications, electrical transport in these remains poorly understood because of a lack of single crystal studies. Here, studies of single crystals of two 2D MOFs, Ni3(HITP)2 and Cu3(HHTP)2, uncover critical insights into their structure and transport. Conductivity measurements down to 0.3 K suggest metallicity for mesoscopic single crystals of Ni3(HITP)2, which contrasts with apparent activated conductivity for polycrystalline films. Microscopy studies further reveal that these MOFs are not isostructural as previously reported. Notably, single rods exhibit conductivities up to 150 S/cm, which persist even after prolonged exposure to ambient conditions. These single crystal studies confirm that 2D MOFs hold promise as molecularly tunable platforms for fundamental science and applications where porosity and conductivity are critical.

Structural and electronic switching of a single crystal 2D metal-organic framework prepared by chemical vapor deposition

“…11 ). This value is comparable to conductivity values reported for electrically conductive MOFs and represents one of the few examples of transport measurements taken at the level of a single MOF crystal 11 , 15 , 40 – 43 . Notably, when single-crystal devices of 1 were exposed to the conditions previously used to convert 1 to 2 , a higher conductivity value of 6.22 × 10 –7 S cm –1 was observed (Fig.…”

Experimental evidence for a general model of modulated MOF nanoparticle growth

“…We propose that the seesaw model could be adjusted for such materials by including the formation constants for interlayer stacking. 48 Additionally, these models assume the absence of aggregation, which we expect to play a large role in determining size aer crystallite formation. For MOFs, the relevant diffusing species may be metal ions, linkers, or even entire clusters, given in situ studies that suggest Cu 3 BTC 2 grows by increments of individual Cu 2 BTC 4 paddlewheel units, or even the oriented attachment of small crystals.…”

Electroactive Organic Building Blocks for the Chemical Design of Functional Porous Frameworks (MOFs and COFs) in Electronics

“…[43] Very recently,s tudies of single crystals of Ni 3 (HITP) 2 and Cu 3 (HHTP) 2 revealed conductivitiesu pt o1 50 Scm À1 ,l arger than those obtainedf rom polycrystalline pelletm easurements. [122] Triphenylene building blocks have also been widely explored as buildingb locks for the design of conducting andl uminescent 2D COFs taking advantage of their electrical properties and electron-donor character.T he first example of as emiconductinga nd luminescent COF was reported some time ago by Jiang et al based on the condensation of HHTP and pyrene-diboronic acid. [123] The crystalline porousm aterial exhibited an intense blue luminescence and high electrical current, which was enhanced by iodine doping.…”