Thermodynamically Metastable Thiocyanato Coordination Polymer That Shows Slow Relaxations of the Magnetization

被引:79
作者
Werner, Julia [1 ]
Rams, Michal [2 ]
Tomkowicz, Zbigniew [2 ]
Runcevski, Tomce [3 ]
Dinnebier, Robert E. [3 ]
Suckert, Stefan [1 ]
Naether, Christian [1 ]
机构
[1] Univ Kiel, Inst Anorgan Chem, D-24118 Kiel, Germany
[2] Jagiellonian Univ, Inst Phys, PL-30348 Krakow, Poland
[3] Max Planck Inst Solid State Res, D-70569 Stuttgart, Germany
关键词
SINGLE-CHAIN MAGNETS; CRYSTAL-STRUCTURES; POLYMORPHISM; METAMAGNETISM; ISOMERISM; DESIGN; EXPLORATION; REFINEMENT; NETWORKS;
D O I
10.1021/ic503029t
中图分类号
O61 [无机化学];
学科分类号
070301 ; 081704 ;
摘要
Reaction of cobalt thiocyanate with 4-acetylpyridine leads to the formation of [Co(NCS)(2)(4-acetylpyridine)(2)](n) (3/I). In its crystal structure the Co cations are connected by pairs of mu-1,3-bridging thiocyanato ligands into dimers that are further connected into layers by single anionic ligands. DTA-TG measurements of Co(NCS)(2)(4-acetyl-pyridine)(4) (1) led to the formation of 3/I. In contrast, when the hydrate Co(NCS)(2)(4-acetyl-pyridine)(2)(H2O)(2) (2) is decomposed, a mixture of 3/I and a thermodynamically metastable form 3/II is obtained. Further investigations reveal that thermal annealing of 2 leads to the formation of 3/II, that contains only traces of the stable form 3/I. DSC and temperature dependent X-ray powder diffraction (XRPD) measurements prove that 3/II transforms into 3/I on heating. The crystal structure of 3/II was determined ab initio from XRPD data. In its crystal structure the Co cations are linked by pairs of bridging thiocyanato anions into a 1D coordination polymer, and thus, 3/II is an isomer of 3/I. Magnetic measurements disclose that the stable form 3/I only shows paramagnetism without any magnetic anomaly down to 2 K. In contrast, the metastable form 3/II shows ferromagnetic behavior. The phase transition into ordered state at T-c = 3.8 K was confirmed by specific heat measurements. Alternating current susceptibility measurements show frequency dependent maxima in chi' and chi '' which is indicative for a slow relaxation of the magnetization.
引用
收藏
页码:2893 / 2901
页数:9
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