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Three New Niccolites: High‐Temperature Phase Transitions, Prominent Anisotropic Thermal Expansions, Dielectric Anomalies, and Magnetism
Author(s) -
Zhao YinHua,
Liu Shu,
Wang BingWu,
Wang ZheMing,
Gao Song
Publication year - 2019
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.201901655
Subject(s) - condensed matter physics , antiferromagnetism , dielectric , phase transition , phase (matter) , anisotropy , magnetization , materials science , chemistry , crystallography , magnetic field , physics , optoelectronics , organic chemistry , quantum mechanics
Three new iso‐structural ammonium metal formates of [dmpnH 2 ][M 2 (HCOO) 6 ], in which dmpnH 2 2+ = N , N ′‐dimethyl‐1,3‐propylenediammoium and M=divalent Co, Zn and Mg ions, are reported. They possess niccolite metal formate frameworks with long‐shaped cavities for the accommodation of dmpnH 2 2+ cations. The three materials display reversible phase transitions of similar mechanism from ordered, antipolar or antiferroelectric, low‐temperature phases in space group C 2/ c , to disordered, paraelectric, high‐temperature phases in space group P 3 ‾ 1 c , with quite high critical temperatures of 366, 370, and 334 K for Co, Zn, and Mg members, respectively. On warming, the dmpnH 2 2+ cation experiences an ordered state with gradual increase of the local vibration motions of the central CH 2 and terminal CH 3 groups, a partially disordered state with gradually enhanced flipping motion between the major and minor orientations, and finally a twisting or rotating motion after the phase transition, accompanied by prominent anisotropic thermal expansions and dielectric anomalies/relaxations. The phase transition characters and relevant properties also exhibit a subtle metal‐dependence. The Co member shows spin‐canted antiferromagnetism below the Néel temperature of 16.1 K, with unusual large spontaneous magnetization and coercive field.