1508 | J. Mater. Chem. C, 2017, 5, 1508--1513 This journal is © The Royal Society of Chemistry 2017 Cite this: J. Mater. Chem. C, 2017, 5, 1508 Zn(II)-based metal–organic framework: an exceptionally thermally stable, guest-free low dielectric material† Shruti Mendiratta, ab Muhammad Usman, a Chun-Chi Chang, a Yung-Chi Lee, c Jenq-Wei Chen, d Maw-Kuen Wu, c Ying-Chih Lin,* b Chao-Ping Hsu* a and Kuang-Lieh Lu* a The synthesis of an exceptionally thermally stable, chemically stable, guest-free low-k dielectric metal–organic coordination framework [Zn 2 (Hbbim) 2 (bbim)] n ( 1,H 2 bbim = bisbenzimidazole) was achieved under hydrothermal conditions. Structural analysis showed that compound 1 crystallizes in a triclinic space group P1 and possesses a guest-free structure. Compound 1 was found to be a low-k dielectric material (3.05 at 1 MHz) that was extremely robust towards various solvents. The compound was exceptionally thermally stable and retained its structure at temperatures of up to 450 1C. Temperature-dependent dielectric studies revealed that 1 has a low-dielectric constant that remains stable upon increasing the temperature. This low- dielectric constant was further supported by density functional theory calculations, which showed that the dielectric property can be mainly attributed to electronic polarizability. Introduction Dielectric materials have a profound impact on the performance of interlayer dielectrics (ILD) in semiconducting devices. Insulating dielectrics are required in digital circuits as an insulating medium to separate the conducting parts (wire interconnects and transistors) from one another and to function as a supporter of an electrostatic field. 1–3 Materials with extremely low-dielectric constants ( k o 3.9 as in SiO 2 ) have been targeted as interlayer dielectrics because they decrease the cross-talk noise, propagation delay, and power dissipa- tion in most electronic components. 4 With the miniaturization of most devices, the introduction of new low- k dielectrics as insulating materials becomes inevitable. A wide variety of materials, such as porous silsesquioxanes, doped oxides, aromatic polymers, and xerogels, have been proposed to replace the amorphous silica films that are currently in use. 5–7 However, introducing these materials along with miniaturization results in materials with weak thermomechanical properties and integration challenges. The concept of rational material design has been realized to a large extent in metal–organic frameworks (MOFs) because of their high functional tunability and the fact that their pore sizes can be adjusted from a few angstroms to several nanometers. 8–20 A few research groups have shown that MOFs are potential candidates for use as dielectric, ferroelectric, multiferroic, and low-k materials. 21–24 However, in addition to having low-k properties, a MOF that also exhibits high thermal stability and chemically stable characteristics as well as adopts a guest- free structure is still not reported in the literature. Herein, we report a remarkable Zn-based MOF [Zn 2 (Hbbim) 2 (bbim)] n (1,H 2 bbim = bisbenzimidazole), which possesses all of the above-mentioned features. To the best of our knowledge, to date, the low dielectric property of this coordination polymer with exceptional thermal stability, chemical stability, and a guest-free structure has not been reported. Furthermore, the low dielectric property of an MOF was simultaneously examined from the standpoint of both experimental studies and theoretical calculations. Results and discussions Synthesis The compound [Zn 2 (Hbbim) 2 (bbim)] n (1,H 2 bbim = bisbenz- imidazole) was synthesized in high yield from Zn(NO 3 ) 2 Á6H 2 O and H 2 bbim in an aqueous methanol solution at 180 1C under hydrothermal conditions via a single-step, self-organization process (Scheme 1). The choice of an appropriate organic a Institute of Chemistry, Academia Sinica, Taipei 115, Taiwan. E-mail: kllu@gate.sinica.edu.tw; Tel: +886-2-27898518 b Department of Chemistry, National Taiwan University, Taipei 106, Taiwan c Institute of Physics, Academia Sinica, Taipei 115, Taiwan d Department of Physics, National Taiwan University, Taipei 106, Taiwan † Electronic supplementary information (ESI) available: Coordination modes of H 2 bbim, DSC, PXRD, crystallographic data, atomic coordinates, isotropic displace- ment parameters and theoretical calculations performed on 1. CCDC 1492702. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/ c6tc05314a Received 9th December 2016, Accepted 11th January 2017 DOI: 10.1039/c6tc05314a rsc.li/materials-c Journal of Materials Chemistry C PAPER Published on 17 January 2017. Downloaded by Academia Sinica - Taipei on 07/03/2017 04:29:31. View Article Online View Journal | View Issue