Tuning of the Critical Temperature in Magnetic 2D Coordination Polymers by Mixed Crystal Formation

• Published in: Crystal growth & design 2018-05, Vol.18 (5), p.3117-3123
• Main Authors: Wellm, Carsten, Rams, Michał, Neumann, Tristan, Ceglarska, Magdalena, Näther, Christian
• Format: Article
• Language: English
• ISSN: 1528-7483; 1528-7505
• DOI: 10.1021/acs.cgd.8b00245

Reaction of Co­(NCS)2 and Ni­(NCS)2 with 4-acetylpyridine under different conditions leads to the formation of mixed crystals of the layered compound with the composition [Co x Ni1–x (NCS)2(4-acetylpyridine)2] n (x = 0.15 0.3, 0.5, and 0.7). Mixed crystal formation was investigated by a combination of X-ray powder diffraction (XRPD), atomic absorption spectroscopy (AAS), simultaneous scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX), differential scanning calorimetry (DSC), and magnetic and heat capacity measurements. Dependent on the synthetic method, homo- or heterogeneous mixed crystals were obtained as already indicated by XRPD, where significant differences to the pattern of physical mixtures of the homometallic counterparts [M­(NCS)2(4-acetylpyridine)2] n with M = Co or Ni) with the same Co/Ni ratio are observed. Mixed crystals can also be obtained from physical mixtures under thermodynamic control, indicating that they are more stable than the homometallic compounds. This is further supported by AAS, which indicates that the solubility of the mixed crystals is lower than that of the homometallic compounds. Magnetic and heat capacity measurements show a linear increase of the critical temperature of magnetic ordering with increasing Ni content and also confirm that homogeneous samples were obtained.