Trinuclear Triplesalophen Building Blocks with Terminal Cyanides and Implications for the Spin‐Polarization Mechanism for Low‐Spin Fe^III and Cr^III Ions

Abstract

In order to further optimize our triplesalen-based single-molecule magnets, we have synthesized the triplesalophen ligand H 6 baron Me , where the completely sp 2 -hybridized ligand backbone should enable almost planar complexes. Here, we report the new complexes [(baron Me ){Fe III Cl} 3 ], [(baron Me )-{Fe III (CN) 2 } 3 ] 3-, and [(baron Me ){Cr III (CN) 2 } 3 ] 3-. As intended the local anisotropy axes, defined by the cyanide ligands, deviate only by ten degrees from the molecular C 3 -axis. The exchange coupling in [(baron Me ){Fe III (CN) 2 } 3 ] 3is ferromagnetic with J = 2.2 cm -1 but antiferromagnetic in [(baron Me ){Cr III (CN) 2 } 3 ] 3with J = -1.76 cm -1 . The ferromagnetic coupling in the Fe III low-spin complex is rationalized by a good π overlap of the d yz magnetic [a] 4987 orbital with the O(p z ) orbitals of the central phloroglucinol unit. The three unpaired electrons of the Cr III ions in [(baron Me )-{Cr III (CN) 2 } 3 ] 3provide competing spin-delocalization and spinpolarization pathways, which explains the overall antiferromagnetic coupling. These two complexes are the first l.s. Fe III and Cr III complexes of triplesalen-like ligands and emphasize the strong impact of the specific electronic configuration on the spin-polarization mechanism via the central phloroglucinol. The potential of [(baron Me ){Fe III (CN) 2 } 3 ] 3and [(baron Me ){Cr III -(CN) 2 } 3 ] 3as molecular building blocks for nonanuclear complexes by coordination to the six cyanides is discussed.have been prepared and characterized with many exhibiting interesting single-molecule magnet properties. [15][16][17][18][19][20][21][22][23][24] Scheme 1. Specific triplesalen and triplesalophen ligands. Scheme 2. Schematic presentation of the application of a [(baron Me ){M(CN) 2 } 3 ] 3building block for the supramolecular assembly of a) nonanuclear SMMs or b) triple-stranded 1D SCMs.the molecular building blocks enforcing a stronger collinearity of the local anisotropy tensors. In analogy to the successful synthesis of trinuclear SMMs by bridging two mononuclear salen complexes by a molecular building block with two trans coordinated cyano ligands, [4,5,27] our trinuclear triplesalophen complexes should be used as molecular building blocks for either nonanuclear SMMs (Scheme 2a) or triple-stranded one-dimensional single-chain magnets (Scheme 2b). We could already synthesize square-planar coordinated trinuclear Ni II 3 , Cu II 3 , and Co II 3 triplesalophen. [26,[28][29][30] Here, we report the first synthesis of the trinuclear molecular building blocks [(baron Me )-{Fe(CN) 2 } 3 ] 3and [(baron Me ){Cr(CN) 2 } 3 ] 3with six coordinated cyano ligands. These are also the first l.s. Fe III and Cr III complexes of extended phloroglucinol complexes that we have been unable to synthesize with any of our other ligands so far. That provides the opportunity to study the magnetic exchange mediated via the phloroglucinol for l.s. Fe III and Cr III ions for the first time. The coupling is ferromagnetic for l.s. Fe III and antiferromagneti...

Metal–Metal BondUmpolungin Heterometallic Extended Metal Atom Chains

“…Use of an analogous synthetic route for other Mo 2 M­(dpa) 4 (OTf) 2 HEMACs is complicated by the fact that Cr­(OTf) 2 is not commercially available and that other anhydrous M­(OTf) 2 salts, despite being commercially available, are inconsistently characterized and in our hands give inconsistent results. We therefore considered several methods for preparing M­(OTf) 2 starting materials, − ultimately settling on the precipitation of an insoluble salt. , We found that reaction of MCl 2 (M = Cr, Mn, Fe, Co, and Ni) with 2.0 equiv of TlOTf in CH 3 CN affords the M­(OTf) 2 salts in good yields and high purity (Scheme A). This preparation involves the initial formation of a soluble, heteroleptic M­(CH 3 CN) x (OTf) 2 complex and precipitation of TlCl.…”

Optimization of Single‐Molecule Magnets by Suppression of Quantum Tunneling of the Magnetization

“…Ferromagnetic interactions could also be established between V IV , Ni II ( S = 1), Co II l.s . and Fe III l.s . ions.…”