Cyanide-Bridged Fe-Co Polynuclear Clusters Based on Four-Coordinate Cobalt(II)

Abstract

Treatment of CoCl 2 •6H 2 O and tris(pyrazolyl-1-yl)borate tricyanoiron(III) anions at 55 °C afforded a series of new Fe-Co polynuclear clusters: {Co 2 Cl 2 (DMF) 4 [(Tp 4-Me )Fe(CN) 3 ] 2 } (1; Tp 4-Me = hydridotris(4methylpyrazol-1-yl)borate), (H 3 O + )@{Co 4 Cl 4 [(Tp 4-Me )Fe(CN) 3 ] 4 } (2), (MePh 3 P) 4 {Co 6 Cl 6 [(Tp 4-Me )Fe(CN) 3 ] 6 }•15CH 3 CN•3CH 3 OH•2H 2 O (3), and (BnEt 3 N) 4 {Co 5 Cl 8 [(Tp*)Fe(CN) 3 ] 4 }•4CH 3 CN•2H 2 O (4; Tp*= hydridotris(3,5dimethylpyrazol-1-yl)borate). They feature an asymmetric [Fe 2 Co 2 (CN) 4 ] square, a pseudocubic [Fe 4 Co 4 (CN) 12 ] cluster, a distorted-hexagonal-prism-shaped [Fe 6 Co 6 (CN) 18 ] cage, and a bis(trigonal-bipyramidal) cluster of [Fe 4 Co 5 (CN) 12 ] fused at one cobalt center, respectively. The Co(II) ions adopt a four-coordinate tetrahedral geometry except for half of 1 in an octahedral geometry. It should be mentioned that 3 and 4 provide two novel molecular skeletons in the cyanometalate family. Interestingly, 1 behaved as a single-molecule magnet with an effective energy barrier for spin reverse of 30.7 K at zero dc field. Our result demonstrated a possible self-assembly route toward high-nuclearity cyanide-bridged clusters by introducing four-coordinate cobalt(II) ions.

Azido-Cyanide Mixed-Bridged FeIII–NiII Complexes

“…The obtained J values further confirm the ferromagnetic coupling between Fe III –Ni II and Ni II –Ni II ions, suggesting an S T = 3 ground spin state. All of the fitting results are comparable to those reported for cyanide-bridged Fe III –Ni II complexes containing [(Tp R )­Fe­(CN) 3 ] − units and azide-bridged Ni­(II) complexes. − Accordingly, using an S T = 3 macro-spin model with the following spin Hamiltonian (eq ), the magnetization data were fitted with the PHI program to extract the axial and transverse ( E ) zfs parameters of the entire molecule (Figure S13): …”

“…Moreover, the [(Tp R )­Fe­(CN) 3 ] − anions have also been widely used for constructing charge transfer systems because the electronic properties of the building block can be systematically modified through chemical modification . Self-assembly of these anions with either fully solvated metallic salts [M II (sol) n ] 2+ or partly coordinated [(L)­M­(sol) m ] 2+ units (L = chelate ligand) afforded a series of low-dimensional complexes, such as dinuclear complexes, squares, cubes, and one-dimensional (1D) chains with fascinating magnetic properties . Remarkably, the realization of good alignments (colinear or parallel) of the B···Fe vectors in these structures may help contribute to the SMM behavior, as evidenced in a series of Fe–Ni complexes ([Fe III 2 Ni II ], [Fe III 4 Ni II 2 ], and [Fe III 6 Ni II 3 ]) with a general motif of [Fe 2 Ni] n (Scheme ).…”

Polyoxometalate-Assisted Assembly of Pearl-Chain-Like Cyanide-Bridged Single-Chain Magnets

“…In addition, the primary difference in structure between 1 and 2 ( 3 ) can be explained by the charge density match. , The more highly negatively charged [SiW 12 O 40 ] 4– will facilitate the formation of the more positively charged {Fe 2 M 3 } n chain species (+4 per unit) rather than the {Fe 2 M 2 } square species (+2 per unit). It should be mentioned that the use of triflate instead of chloride salts may avoid the formation of the asymmetric square complex {Co 2 Cl 2 (DMF) 4 [(Tp 4‑Me )­Fe­(CN) 3 ] 2 } (Tp 4‑Me = hydridotris­(4-methylpyrazol-1-yl)­borate) reported previously by us . A TGA analysis revealed that the sample of 1 desolvated and decomposed easily with a continuous weight loss above room temperature, while those of 2 and 3 showed a relatively stable plateau before a quick weight loss of 8.4–9.9% at around 120 °C, significantly greater than the calculated value (4.5%) for the lattice DMF molecules, indicating that part of the coordinating DMF molecules are lost in this process (Figures S1–S3).…”

“…However, very limited success has been achieved in introducing POMs into the cyanometalate system. We presumed that these highly negatively charged species might facilitate the generation of highly positively charged {Fe–CN–M} moieties as counteranions from the perspective of charge density matching . In addition, these diamagnetic nanosized POMs will necessarily result in the good separation of the individual molecules, an important aspect for reducing the intermolecular interaction .…”

Thermally Induced Reversible Metal-to-Metal Charge Transfer in Mixed-Valence {Fe III 4 Fe II 4 } Cubes

“…With long-standing interest in the switchable materials based on [(Tp R )Fe(CN) 3 ] − (Tp R = poly(pyrazol-1yl)borate) building blocks,[37][38][39][40] we recently turned our interest in a series of {Fe III Fe II } complexes for better understanding this encrypted system. Herein, we prepared two new cubic mixed-valence {FeIII …”