Four novel 3D RE-MOFs based on maleic hydrazide: Syntheses, structural diversity, efficient electromagnetic wave absorption and antibacterial activity properties

Abstract

Maleic hydrazide (MH), a six-membered heterocycle, contains two rigid lactam groups. Although MH has more than one coordination site, structural information regarding its metal organic frameworks (MOFs), especially rare-earth metal organic frameworks (RE-MOFs), is barely reported. In this work, four novel RE-MOFs [Y2(MH)6]n·DMF (1), [Er2(MH)6]n (2), [Yb2(MH)6]n (3), and [La(MH)3]n (4) were successfully synthesized by hydrothermal reactions and characterized by single-crystal X-ray diffraction, IR spectroscopy, elemental analyses, powder X-ray diffraction (PXRD) and thermogravimetric analyses (TGA). The organic linkers bind to the central metal ions through oxygen atoms in MOFs 1–3 (isostructural), and the organic linkers bind to the central ions through both oxygen atoms and nitrogen atoms in MOF 4. The electromagnetic wave absorption (EMWA) studies of MOFs 1–4 demonstrate that these MOFs with special porous structures have impressive EMWA performance. A maximum reflection loss (RL) value of −22.78 dB, with a broad effective absorption bandwidth of 2.24 GHz, can be obtained for MOF 1. Additionally, for MOF 2, a maximum RL value of −20 dB can be obtained. Both MOF 3 and MOF 4 have narrow effective EMWA bandwidths with maximum RL values of −28.14 dB and −13.07 dB. The excellent EMWA property may be attributed to the synergetic and complementary effects of permittivity and permeability. Additionally, MOFs 1–4 were tested for antibacterial activity. The results show that all the tested MOFs exhibit significant antibacterial properties. In particular, MOF 4 has the strongest antibacterial activity against two tested pathogenic bacteria compared to MOFs 1–3.