Magneto-structural correlations in a family of di-alkoxo bridged chromium dimers

Abstract

A series of di-alkoxo bridged Cr(iii) dimers have been synthesised using pyridine alcohol ligands. The structures fall into four general categories and are of formula: [Cr(OMe)(pic)]·½MeOH·½EtO (1), [Cr(hmp)(pic)X] (where X = Cl (2), Br (3)), [Cr(L)Cl(A)]·2S (where L = hmp, A = HO and S = EtO (4); L = hmp, A = pyridine and S = pyridine (5); L = hmp, A = 4-picoline and no S (6); L = hep, A = HO and S = MeCN (7)), and [Cr(hmp)(hmpH)Cl]·MeCN (8). Direct current (DC) magnetic susceptibility measurements show relatively weak antiferromagnetic exchange interactions between the Cr(iii) centres with J values <|15| cm in all of the complexes measured. DFT calculations performed on complexes 1-8 reproduce both the sign and strength of the exchange interactions found experimentally, and confirm that the magnitude and sign of the J value is strongly dependent upon the orientation of the dihedral angle formed between the bridging CrO plane and the O-R vector of the bridging group (θ), and the Cr-O-Cr-O dihedral angle (ψ).

Synthesis and Characterisation of Luminescent [CrIII2L(μ‐carboxylato)]3+ Complexes with High‐Spin S=3 Ground States (L=N6S2 donor ligand)

“…The experimental J values for 1 and 2 are the largest yet reported for ferromagnetically coupled chromium(III) complexes and surpass the coupling in the related bis-μ-alkoxido-μcarboxylato bridged Cr III dimers by a factor of 3. [26,37] This finding is consistent with the observation that thiolato bridges can more efficiently propagate magnetic exchange interactions. [69,70] The ferromagnetic exchange interactions found for 1 and 2 are also in contrast to the antiferromagnetic (AFM) exchange interactions present in [Cr 2 (L N2S ) 3 ] 3 + (J = À 39 cm À 1 (H = À 2JS 1 S 2 )).…”

“… [20] The intensity enhancement of transitions involving ligand‐field states (LF) has also been a well‐known effect of binuclear interactions in chromium(III) dimers. The vast majority of exchange‐coupled chromium(III) complexes employ bridging oxido,[ 21 , 22 , 23 ] hydroxido,[ 24 , 25 ] alkoxido, [26] halido, [27] and carboxylato [28] ligands. Recently, a number of semiquinoid radical bridging ligands have been used to obtain large magnetic exchange interactions between Cr III centers.…”

Pentanuclear Spirocyclic Ni4Ln Derivatives: Field Induced Slow Magnetic Relaxation in the Dysprosium and Erbium Analogues

“…3d and 4f metal ions in a same compound is not a trivial task. Chemists have to devise appropriate organic ligands with specific functionalities for preferential aggregation of both 3d and 4f metal ions, at the same time where magnetic exchanges can occur among the metal centres via a suitable single‐atom or by means of multiatom bridges . Based on the above requirements in mind we prepared a new chelating, multisite, coordinating Schiff base ligand ( E )‐2‐(hydroxymethyl)‐6‐{[(2‐hydroxyphenyl)‐imino] methyl}‐4‐methylphenol (LH 3 ), leading to the formation of heterometallic 3d/4f complexes.…”

A simple methodology for constructing ferromagnetically coupled Cr(iii) compounds

“…Indeed, the "GHP" model also failed to reproduce the data for a previously reported family of [Cr(OR)] 2 dimers where the hydroxide bridges were replaced with alkoxide bridges. 13 The net exchange J has two contributions, J AFM and J FM , denoting the antiferromagnetic and ferromagnetic parts, respectively. Qualitative models based on Hey-ThibeaultHoffmann (HTH) and Kahn methodologies are widely used to analyse the origin of magnetic exchange in dinuclear complexes.…”