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

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 [Y-2(MH)(6)](n)center dot DMF (1), [Er-2(MH)(6)](n) (2), [Yb-2(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.