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Dynamic Motion of Organic Ligands in Polar Layered Cobalt Phosphonates
Author(s) -
Cai ZhongSheng,
Hoshino Norihisa,
Bao SongSong,
Jia Jiage,
Akutagawa Tomoyuki,
Zheng LiMin
Publication year - 2018
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201801301
Subject(s) - phosphonate , polar , space group , cobalt , crystallography , chemistry , antiferromagnetism , stereochemistry , dielectric , group (periodic table) , materials science , inorganic chemistry , organic chemistry , x ray crystallography , condensed matter physics , physics , optoelectronics , astronomy , diffraction , optics
By introducing the polar methoxy group into phenyl‐ or benzyl‐phosphonate ligands, four cobalt phosphonates with layered structures are obtained, namely, [Co(4‐mopp)(H 2 O)] ( 1 ), [Co(4‐mobp)(H 2 O)] ( 2 ), [Co(3‐mopp)(H 2 O)] ( 3 ), and [Co(3‐mobp)(H 2 O)] ( 4 ), where 4‐ or 3‐moppH 2 is (4‐ or 3‐methoxyphenyl)phosphonic acid and 4‐ or 3‐mobpH 2 is (4‐ or 3‐methoxybenzyl)phosphonic acid. Compounds 1 , 2 , and 4 crystallize in the polar space groups Pmn 2 1 or Pna 2 1 , whereas compound 3 crystallizes in the centrosymmetric space group P 2 1 / n . The layer topologies in the four structures are similar and can be viewed as perovskite type, where the edge‐sharing [Co 4 O 4 ] rhombi are capped by the PO 3 C groups. The phenyl and MeO groups in compounds 1 – 3 are heavily disordered, whereas that in 4 is ordered. Structural comparison based on the data at 296 and 123 K reveals distinct dynamic motion of the organic groups in compounds 1 and 2 . The fluctuation of the polar MeO groups in these two compounds is confirmed by dielectric relaxation measurements. In contrast, the fluctuation of polar groups in compounds 3 and 4 is not evident. Interestingly, the dehydrated samples of 3 and 4 (i.e., 3 ‐de and 4 ‐de) exhibit one‐step and two‐step phase transitions associated with the motion of polar organic groups, as proven by DSC and dielectric measurements. The magnetic properties of compounds 1 – 4 are investigated, and strong antiferromagnetic interactions are found to mediate between the magnetic centers through μ‐O(P) and O‐P‐O bridges.