Influence of the co-Ligand on the Magnetic and Relaxation Properties of Layered Cobalt(II) Thiocyanato Coordination Polymers

Abstract

Reaction of Co(NCS)2 with 1,2-bis(4-pyridyl)-ethane (bpa) leads to the formation of [Co(NCS)2(bpa)2]n, which, on heating, transforms into the new layered coordination polymer [Co(NCS)2(bpa)]n. This compound can also be prepared in solution, but because no reasonable single crystals are available, its crystal structure was determined from X-ray powder data from scratch. In the crystal structure of [Co(NCS)2(bpa)]n, the cobalt(II) cations are coordinated by two S-bonded and two N-bonded thiocyanato anions and two N atoms of the bpa co-ligands in a distorted octahedral geometry. The cobalt(II) cations are linked into chains by pairs of μ-1,3 bridging thiocyanato anions. These chains are further connected into layers by the 1,2-bis(4-pyridyl)-ethane ligand. The compound was magnetically characterized, and, for comparative purposes, the complementary magnetic study of a known and very similar compound, [Co(NCS)2(bpe)]n (bpe = 1,2-bis(4-pyridyl)-ethylene), was also undertaken. The compounds differ in their interchain interactions, which are antiferromagnetic but significantly greater for [Co(NCS)2(bpe)]n. Magnetic measurements indicate that [Co(NCS)2(bpa)]n is a canted antiferromagnet with Néel temperature TN = 3.1 K and that Co(NCS)2(bpe) is an antiferromagnet with TN = 4.0 K. Both compounds show a metamagnetic transition with a critical field HC ∼ 40 Oe and ∼ 400 Oe, respectively. Magnetic relaxations were studied by means of dc and ac methods and analyzed using the Argand diagrams. Except for the thermally activated single chain and domain wall relaxations observed for both compounds, temperature-independent slow relaxations were observed for [Co(NCS)2(bpa)]n.

Synthesis, structure and properties of [Co(NCS)2(4-(4-chlorobenzyl)pyridine)2]n, that shows slow magnetic relaxations and a metamagnetic transition

“…56,57 [Fe(NCSe) 2 ( pyridine) 2 ] n is also a metamagnet but it shows slow relaxation of magnetization and it is assumed that the lower magnetic anisotropy of Fe(II) cations is compensated by stronger intrachain interactions. 39,61 We also tried to investigate the influence of the interchain interactions by using the relatively large 4-(3-phenylpropyl)pyridine as a coligand. This includes, e.g., [Co(NCS) 2 (4-acetylpyridine) 2 ] n that exhibits a ferromagnetic ground state.…”

Synthesis, crystal structures and properties of Ni(NCS)2-4-(hydroxymethyl)pyridine coordination compounds

“…Our interest is focused on 1D thio-and selenocyanato compounds of composition [M(NCS) 2 (L) 2 ] n (M = Mn, Fe, Co and Ni; L = neutral monodentate N-donor co-ligand), in which the paramagnetic transition metal cations Mn, Fe, Co and Ni are linked by pairs of l-1,3-bridging anionic ligands into chains [51][52][53][54][55][56][57][58][59]. Such chain compounds are frequently observed and thus, it can be assumed that this is a very stable arrangement.…”

Synthesis, Structures, and Physical Properties of Thiocyanate Coordination Compounds with 3‐Hydroxymethylpyridine

“…[35][36][37][38][39][40][41] Unfortunately, these metal cations are not very chalcophilic and therefore, the bridging compounds are frequently difficult to obtain. In some cases, they can be synthesized from solution using an excess of the metal thiocyanate but there are many examples in which such compounds cannot be obtained as phase pure samples or are not accessible from solution.…”