Magnetic Anisotropy and Field‐induced Slow  Relaxation of Magnetization in Tetracoordinate CoII Compound [Co(CH3‐im)2Cl2]

Abstract

Static and dynamic magnetic properties of the tetracoordinate CoII complex [Co(CH3-im)2Cl2], (1, CH3-im = N-methyl-imidazole), studied using thorough analyses of magnetometry, and High-Frequency and -Field EPR (HFEPR) measurements, are reported. The study was supported by ab initio complete active space self-consistent field (CASSCF) calculations. It has been revealed that 1 possesses a large magnetic anisotropy with a large rhombicity (magnetometry: D = −13.5 cm−1, E/D = 0.33; HFEPR: D = −14.5(1) cm−1, E/D = 0.16(1)). These experimental results agree well with the theoretical calculations (D = −11.2 cm−1, E/D = 0.18). Furthermore, it has been revealed that 1 behaves as a field-induced single-ion magnet with a relatively large spin-reversal barrier (Ueff = 33.5 K). The influence of the Cl–Co–Cl angle on magnetic anisotropy parameters was evaluated using the CASSCF calculations.

Effect of Coordination Geometry on Magnetic Properties in a Series of Cobalt(II) Complexes and Structural Transformation in Mother Liquor

“…The structural parameter δ proposed by Bocǎ et al was based on two angles, ∠(X-Co-X) (α) and ∠(Y−Co−Y) (β) for [CoX 2 Y 2 ] complexes, as δ = 2α Td − (α + β), where α Td = 109.5°, and it was suggested that this should directly correlate with D. 77 A later study by Nemec et al showed that such a relationship between δ and D is not linear in general. 78 In case of tetracoordinate [Co(NCS) 4 ] 2− of 1, the homoleptic nature of this complex made it difficult to calculate δ; however, the symmetry is close to ideal T d symmetry for which D = 0 and, indeed, the CASSCF/ NEVPT2 calculation resulted in a very small D value of −1.23 cm −1 (Table 2). Also, other homoleptic tetrahedral complexes of Co II were studied, 79 and an attempt to correlate D with the continuous symmetry measure (CShM) of SHAPE was reported.…”

“…To discuss the relationship between the geometry of the coordination polyhedron and the magnetic anisotropy, we start with tetracoordinate Co II complexes. 78 In case of tetracoordinate [Co(NCS) 4 ] 2− of 1, the homoleptic nature of this complex made it difficult to calculate δ; however, the symmetry is close to ideal T d symmetry for which D = 0 and, indeed, the CASSCF/ NEVPT2 calculation resulted in a very small D value of −1.23 cm −1 (Table 2). Also, other homoleptic tetrahedral complexes of Co II were studied, 79 and an attempt to correlate D with the continuous symmetry measure (CShM) of SHAPE was reported.…”

Halogen Bonding in New Dichloride-Cobalt(II) Complex with Iodo Substituted Chalcone Ligands

“…Crystals 2020, 10, x FOR PEER REVIEW 2 of 14 choice of coordination number and polyhedral symmetry. It is well established that, for Co(II) compounds, very interesting results can be achieved for tetracoordinate coordination compounds exhibiting large distortion from ideal tetrahedral geometry [27]. To achieve significant distortions of coordination geometry, one can assume two viable strategies: (a) use of polydentate and sufficiently rigid ligands, (b) use of monodentate bulky ligands.…”

Co(ii)-Based single-ion magnets with 1,1′-ferrocenediyl-bis(diphenylphosphine) metalloligands

“…13 It reads δ = 2α Td − (α), where α Td is the angle of the ideal tetrahedron (109.5°), α is the angle between the two Co-N/P bonds. Despite some limitations, 14 this relationship has proved to be successful in the prediction of sign and magnitude of D, such that more negative/positive δ should lead to more negative/positive value of D. Therefore, our attention has focused on compounds with rather large and negative parameter δ and these were further investigated for their static and dynamic magnetic properties. 14,15 Therefore, we opted to investigate the compound [CoCl 2 (dppf )] as a suitable SIM candidate, where dppf represents the 1,1′-ferrocenediyl-bis (diphenylphosphine).…”

“…Despite some limitations, 14 this relationship has proved to be successful in the prediction of sign and magnitude of D, such that more negative/positive δ should lead to more negative/positive value of D. Therefore, our attention has focused on compounds with rather large and negative parameter δ and these were further investigated for their static and dynamic magnetic properties. 14,15 Therefore, we opted to investigate the compound [CoCl 2 (dppf )] as a suitable SIM candidate, where dppf represents the 1,1′-ferrocenediyl-bis (diphenylphosphine). This complex can be prepared by the reaction between dppf and CoCl 2 where both dppf and the resulting product [CoCl 2 (dppf )] are very well known, thoroughly studied (besides magnetic properties) 16 and even commercially available coordination compounds.…”