Coordination Chemistry of N,N,N′,N′‐Tetraethylpyridine‐2,6‐dithiocarboxamide (S‐dept) – X‐ray Crystal Structures and Magnetic Properties of [Co(S‐dept)X₂] (X = Br, I, and NCS)

Abstract

Mononuclear cobalt(II) complexes [Co(S‐dept)X2] [X = Br (1), I (2) and NCS (3)] were synthesized using N,N,N′,N′‐tetraethylpyridine‐2,6‐dithiocarboxamide (S‐dept), and characterised by conductivity, spectral and single‐crystal X‐ray diffraction studies. These studies reveal that the compounds consist of discrete monomeric molecules in which the cobalt atoms are five‐coordinate in an environment that is best described as being distorted square‐pyramidal. In dimethylformamide the iodo complex shows significant ionic dissociation (1:1 electrolyte) and its crystal field absorption spectrum is interpretable in terms of an octahedral structure [Co(S‐dept)(DMF)2I]+. The temperature dependence of the magnetic susceptibility data is indicative of a high‐spin compound with an important zero‐field splitting. The best fitwas obtained with |D| = 20.5 cm–1 and g = 2.53 for 1, |D| = 14.2 cm–1 and g = 2.38 for 2 and |D| = 17.7 cm–1 and g = 2.35 for 3. The X‐band EPR spectra at low temperature is also characteristic of an S = 3/2 state with important zero‐field splitting. The most important band appears at low fields (ca. 1200 G). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Synthesis and Characterization of 4‐, 5‐, and 6‐Coordinate Tris(1‐ethyl‐4‐isopropylimidazolyl‐κN)phosphine Cobalt(II) Complexes

“…The D values for 2 and 3 agree well with those previously observed for tetrahedral complexes, [43,44] whereas the value for 1, even though somewhat high, is similar to that observed for pentacoordinate high-spin square-pyramid Co II complexes. [45,46] The change from Cl to Br on passing from 2 to 3 affects the ligand field around the Co II ion and, as a result, the values of D and g, [47] and this change can be, at least in part, responsible of the small differences between these parameters observed for 2 and 3.…”

Probing Single-Chain Magnets in a Family of Linear Chain Compounds Constructed by Magnetically Anisotropic Metal-Ions and Cyclohexane-1,2-Dicarboxylate Analogues

“…20 The M(H) plot gives the maximum value of 2.40 µ B at 7 T, which is consistent with a typical value of one uncompensated octahedral Co II ion (Supporting Information, Figure S4). 16,21,22 Compound 6 has a pentanuclear Co II -based spin-chain, as shown in Scheme 3. The dc susceptibility data (Figure 8) measured on a powder sample of 6 show that the χT value of 6 at 320 K is 16.90 cm 3 mol -1 K per Co II 5 , which is significantly larger than the spin-only value of 9.38 cm 3 mol -1 K, hence indicating a large orbital contribution.…”

“…31,32 This suggests that a strongest ligand field effect can be found on the energy level of the Co II ion of the 4-Me-1,2-chdc-Co II system. 16,21,22 Electrostatic potential calculations on a more extended model of a four carboxylate-bridged Co II paddlewheel dimer of 1,2-chdc and 4-Me-1,2-chdc also indicates stronger attraction between the Co II and carboxylates in the 4-Me-1,2-chdc-Co II system (see Supporting Information, Figures S11 and S12 and Table S1), thus further implying that similar results could occur in the fully extended polymeric structures. As some reports show that the D value of five-coordinated Co II has an increasing tendency as the ligand field increased, 16 at least we may expect to perturb the magnetic properties of 2 by replacement of 1,2-chdc into the subtly modified analogue 4-Me-1,2-chdc, although a contrary result was observed for Mn II compounds.…”

“…The M ( H ) plot gives the maximum value of 2.40 μ B at 7 T, which is consistent with a typical value of one uncompensated octahedral Co II ion (Supporting Information, Figure S4). ,, …”

Structure and magnetic property of a mixed-valence nonanuclear cobalt compound with a square-pyramidal CoII5 core

“…The four Co II ions in the basal plane in the octahedral environments represent high-spin centers and exhibit significant spin-orbital coupling, however, the Co II ion in the apical position (Co1) with squarepyramidal coordination may be high-spin or low-spin. Regarding a Co II ion with five-coordination, an increase of the out-of-plane displacement of the Co II ion from 0 to 0.45-0.74 A ˚will stablize the high-spin (S = 3/2) state, 14 thus the out-of-plane displacement of the Co1 ion of 0.58 A ˚indicates a high-spin configuration. In the same way, the d-block orbitals of an ML 5 compound with a square-pyramidal geometry where the angle between the apical and the basal bonds varies from 90 to about 110 • could lead to a rapid decrease in the quartet-state energy, 15a especially when q > 102 • (q = L apical -Co-L basal ).…”