Synthesis and Magnetic Properties of Solid Solutions of Ferromagnetic Layered Coordination Polymers Prepared from Solution and the Solid State

Abstract

Reaction of mixtures of Co­(NCS)2 and Ni­(NCS)2 with ethylisonicotinate in EtOH in a ratio of 1:2 leads to the formation of solid solutions (mixed crystals) of the layered compound [Co x Ni1–x (NCS)2­(ethylisonicotinate)2] n that are always contaminated with an additional crystalline phase. Pure samples of the desired layer compound are accessible by using an excess of the metal salts, but in this case the Co content in the solid solutions, as determined by atomic absorption spectroscopy and energy dispersive X-ray spectroscopy, is always lower than that used in the synthesis. Therefore, solid solutions of Co x Ni1–x (NCS)2­(ethylisonicotinate)4 were synthesized that upon heating transform into solid solutions of the desired layered compound, and in this case the Co/Ni ratio exactly corresponds to that used in the synthesis. The formation of solid solutions of all compounds is already indicated by comparison of the experimental powder X-ray diffraction pattern of the solid solutions with that of physical mixtures with the same Co/Ni ratio. Magnetic and specific heat measurements reveal that the solid solutions show ferromagnetic ordering, as it is the case for the homometallic compounds reported recently, and that the magnetic ordering temperature increases linearly with increasing Ni content. AC measurements show that some Co/Ni inhomogeneity is present, which is more pronounced in the solid solutions prepared via the solid state than in those prepared from solution.

Comparison of the crystal structures of the low- and high-temperature forms of bis[4-(dimethylamino)pyridine]dithiocyanatocobalt(II)

“…In form I, the two Co-N bond lengths to the thiocyanate anions are slightly different, which is not the case in form II (Table 2). Usually this is reflected in the values of the CN stretching vibrations but this is not the case for form I, because two bands are expected but only one is visible in its IR spectrum (Neumann et al, 2018b). Moreover, the Co-N bond lengths to the DMAP ligands are slightly longer in form I compared to form II (Table 2).…”

“…In contrast, if the methanol complex Co(NCS) 2 (DMAP) 2 (MeOH) 2 is thermally decomposed, a new polymorphic modification of Co(NCS) 2 (DMAP) 2 (form I) is obtained. Because we were not able to prepare single crystals of this form, the corresponding Zn complex was prepared and XRPD indicates that it is isotypic to form I of the Co compound (Neumann et al, 2018b). Solvent-mediated conversion experiments reveal that form II is the thermodynamically stable form at room temperature and transforms into form I upon heating.…”

Crystal structure of bis(tetramethylthiourea-κS)bis(thiocyanato-κN)cobalt(II)

“…In this context, we are especially interested in compounds of the general composition [M(NCS) 2 (L) 2 ] n , in which paramagnetic first-row transition-metal cations M such as Mn II , Fe II , Co II or Ni II are octahedrally coordinated by two N-and two S-bonding thiocyanate anions and two coligands L that usually consist of pyridine derivatives. Depending on the nature of the coligand, the metal cations are connected into chains by pairs of -1,3 coordinating anionic ligands (Mautner et al, 2018;Prananto et al, 2017;Shurdha et al, 2013;Jin et al, 2007;Bö hme et al, 2020), or they are linked into layers with different layer topologies (Werner et al, 2015a;Neumann et al, 2018a;Suckert et al, 2016). The chain compounds show either ferromagnetism (Neumann et al, 2019), antiferromagnetism (Jochim et al, 2020) or they represent antiferromagnetic phases of single-chain magnets (Mautner et al, 2018; Rams et al, 2017, 2020; Werner et al, 2015b), whereas the layer compounds are in most cases ferromagnets (Suckert et al, 2016).…”

Synthesis, Crystal Structures and Properties of Polymorphic and Isomeric Nickel(II)thiocyanate Coordination Compounds with 3‐Bromopyridine as Coligand

“…Regarding such 2D networks, compounds based on Co(NCS) 2 and Ni(NCS) 2 are of special interest, because with both cations the magnetic exchange is usually ferromagnetic and at low temperatures ferromagnetic ordering is observed. In this case, the critical temperatures are always higher for Ni(II) than for Co(II), which allows the tuning of the critical temperatures by mixed crystal formation [24–26] …”

“…In this case, the critical temperatures are always higher for Ni(II) than for Co(II), which allows the tuning of the critical temperatures by mixed crystal formation. [24][25][26] In contrast, much more examples for compounds that consist of chains are reported. In nearly all cases the metal cations are octahedrally coordinated and linked into chains by pairs of thiocyanate anions.…”