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A Closer Look: Magnetic Behavior of a Three‐Dimensional Cyanometalate Coordination Polymer Dominated by a Trace Amount of Nanoparticle Impurity
Author(s) -
Lefebvre Julie,
Trudel Simon,
Hill Ross H.,
Leznoff Daniel B.
Publication year - 2008
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.200800259
Subject(s) - superparamagnetism , paramagnetism , materials science , nanoparticle , prussian blue , non blocking i/o , hydrothermal circulation , impurity , transmission electron microscopy , crystallography , octahedron , coordination polymer , polymer , analytical chemistry (journal) , nanotechnology , crystal structure , chemical engineering , magnetization , chemistry , condensed matter physics , magnetic field , organic chemistry , electrochemistry , catalysis , engineering , composite material , quantum mechanics , physics , electrode
The structure and properties of the K{Ni[Au(CN) 2 ] 3 } coordination polymer, prepared as a powder at room temperature and recrystallized hydrothermally, are reported. The structure of K{Ni[Au(CN) 2 ] 3 } contains triply‐interpenetrated Prussian Blue type pseudo‐cubic arrays assembled from the alternation of octahedral Ni II centers and [Au(CN) 2 ] − bridging units. SQUID magnetometry studies have shown that K{Ni[Au(CN) 2 ] 3 } displays typical paramagnetic behavior for isolated Ni II centers down to 1.8 K. However, the magnetic behavior of the samples prepared under hydrothermal conditions suggests a superparamagnetic signature superimposed onto a paramagnetic background. After investigating the samples by transmission electron microscopy, it was determined that, in addition to K{Ni[Au(CN) 2 ] 3 }, the high‐temperature (125, 135, and 165 °C) aqueous reaction of Ni(NO 3 ) 2 ⋅6 H 2 O with KAu(CN) 2 also led to the formation of nanoparticles of NiO and Au as minor side products, and that these dominated the magnetic behavior. Nanoparticles of various sizes and shapes were observed, depending on the reaction conditions. Samples containing nanoparticles were found to be superparamagnetic, exhibiting blocking temperatures of ≈17–22 K, consistent with the behavior expected for NiO nanoparticles. These results illustrate the extreme care that must be taken when examining the physical properties of apparently analytically pure materials prepared by hydrothermal methods.