Intramolecular ferromagnetic interactions in polynuclear metal complexes

Cairns, C.

doi:10.1016/0010-8545(86)85008-1

Cited by 121 publications

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“…Spin Cluster Model. Magnetic interactions in isolated organic polyradicals (e.g., as dilute solutions in diamagnetic solvents) are expected to be dominated by isotropic exchange interactions between “unpaired” electrons. 1c,d In polyarylmethyl high-spin polyradicals, “unpaired” electrons are localized at triarylmethyl sites, with the comparable magnitude of spin density at the trityl carbon and the three adjacent benzene rings. 1d,, Therefore, Heisenberg Hamiltonian, H = −2Σ i > j J ij S i S j , with ferromagnetic couplings ( J ij > 0) between the nearest-neighbor sites should be appropriate as starting point for describing magnetism in such polyradicals. 1cd,, When 1 − 4 are considered as oligomers of spins 1 / 2 , without any assumptions about spin couplings, 1 (trimer) and 2 (pentamer) are exactly solvable while 3 (heptamer) and 4 (hexadecamer) are not solvable by the vector decoupling (Figure ). ,, When J ‘ (1,3-phenylene) ≫ J (3,4‘-biphenylene) ≈ kT for 2 (pentamer), inspection of the Heisenberg Hamiltonian eigenvalues implies that the five highest in energy spin states are negligibly populated (Figure ). Therefore, pentaradical 2 is adequately described by considering population of the five lowest in energy spin states, which correspond to a trimer of the S ‘ = 1, 1 / 2 , and 1 component spins (Figure ) .…”

Section: Resultsmentioning

confidence: 99%

Organic Spin Clusters: Ferromagnetic Spin Coupling through a Biphenyl Unit in Polyarylmethyl Tri-, Penta-, Hepta-, and Hexadecaradicals

1997

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Polyarylmethyl high-spin polyradicals are designed to possess a structure corresponding to simple spin clusters, where component spins (S‘) arise from strong ferromagnetic coupling through 1,3-phenylene units and weak ferromagnetic spin coupling between the component spins is mediated via 3,4‘-biphenylene (or 3,5,4‘-biphenylyne) units. This rational design permits not only modular and highly convergent synthesis of very high-spin molecules but also detailed analysis of their magnetic data. A series of polyether precursors for the corresponding polyarylmethyl tri-, penta-, hepta-, and hexadecaradicals are prepared. The polyradicals are generated and characterized in frozen tetrahydrofuran (or tetrahydrofuran-d 8) solutions, using bulk magnetization studies. The measured values of S, from fits of magnetization vs magnetic field data to Brillouin functions at low temperatures, indicate high-spin ground states; e.g., S = 7.2 vs theoretical S = 8 for hexadecaradical. Estimated yields per site for generation of “unpaired” electrons are as high as 98% for the best samples of penta-, hepta-, and hexadecaradicals. The magnetization vs temperature data are fit to the Boltzman distribution of energy levels, obtained from Heisenberg Hamiltonian; the fits produced ferromagnetic coupling constants (J/k) through 3,4‘-biphenylene units. For tri- and pentaradical, for which exact analytical solutions to the Heisenberg Hamiltonian can be obtained by the vector model, values of J/k ≈ 90 K are obtained. Hepta- and hexadecaradical, which could not be exactly solved by the vector model, are approximated as a dimer of the S‘ = 5/2 and 1 component spins and a trimer of the S‘ = 5/2, 3 and 5/2 component spins, respectively; the corresponding values of J/k, 13 and 4 K, are found to be scaled by the fraction of component spin directly connected through the weak spin coupler (3,4‘-biphenylene unit).

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Section: Resultsmentioning

confidence: 99%

Organic Spin Clusters: Ferromagnetic Spin Coupling through a Biphenyl Unit in Polyarylmethyl Tri-, Penta-, Hepta-, and Hexadecaradicals

1997

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“…The exchange integral J between Cu(II) and Ni(II) is given by means of two individual exchanges: J = 1 / 2 { J [d x 2- y 2 (Cu),d x 2- y 2 (Ni)] + J [d x 2- y 2 (Cu),d z 2 (Ni)]}. The first term must be largely negative as proved for dinuclear Cu(II) complexes; , the second term is believed to be weakly antiferromagnetic …”

Section: Resultsmentioning

confidence: 99%

Migratory Transmetalation in Diphenoxo-Bridged Cu^IIM^II Complexes of a Dinucleating Macrocycle with N(amine)₂O₂ and N(imine)₂O₂ Metal-Binding Sites

et al. 1997

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A phenol-based heterodinucleating macrocycle (H(2)L), comprised of two 2-((methylamino)methyl)-6-(iminomethyl)-4-bromophenolate entities bridged by the -(CH(2))(2)- groups between amine nitrogens and by the -(CH(2))(3)- groups between imine nitrogens, displays dissimilar N(amine)(2)O(2) and N(imine)(2)O(2) metal-binding sites sharing the phenolic oxygens and is prepared as a Cu(II)Pb(II) complex [CuPb(L)](ClO(4))(2). An analogous complex [CuPb(L)(BzO)(dmf)]ClO(4) crystallizes in the triclinic space group P&onemacr;, (No. 2), with a = 13.998(2) Å, b = 15.568(2) Å, c = 8.699(2) Å, alpha = 95.32(1) degrees, beta = 92.23(1) degrees, gamma = 82.81(1) degrees, V = 1871.9(5) Å(3), and Z = 2. Refinements based on 3788 reflections with I > 3.00sigma(I) converged with R = 0.058 and R(w) = 0.069. The Cu(II) resides at the N(imine)(2)O(2) site and assumes a planar geometry. The Pb(II) resides at the N(amine)(2)O(2) site and assumes a seven-coordinate geometry by further addition of a dmf molecule and a bidentate benzoate group. The Cu--Pb separation, doubly bridged by the phenolic oxygens, is 3.466(2) Å. The reaction of [CuPb(L)](ClO(4))(2) with metal(II) sulfate salts provides Cu(II)M(II) complexes [CuM(L)](ClO(4))(2).nH(2)O (M = Mn (n = 2), Co (n = 2), Ni (n = 0), Cu (n = 0), Zn (n = 1)). The CuZn complex, [CuZn(L)(AcO)]ClO(4), crystallizes in the triclinic space group P&onemacr;, (No. 2), with a = 12.290(3) Å, b = 13.402(4) Å, c = 11.501(2) Å, alpha = 95.10(2) degrees, beta = 116.68(2) degrees, gamma = 112.00(2) degrees, V = 1491.8(9) Å(3), and Z = 2. Refinements based on 2497 reflections with I > 3.00sigma(I) converge with R = 0.046 and R(w) = 0.034. The Cu(II) is bound at the N(amine)(2)O(2) site and the Zn(II) is bound at the N(imine)(2)O(2) site with a Cu--Zn separation of 2.942(2) Å. Further, the acetate group bridges the two metal ions providing a five-coordinate geometry about both metal ions. The CuM complexes except for the CuZn complex show significant antiferromagnetic spin-exchange within each dinuclear unit. The CuNi complex shows the ESR spectrum of the spin-doublet ground state which demonstrates the delocalization of the unpaired electron over the CuNi core.

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“…The chemistry of metal complexes with dicompartmental ligands has become a rapidly growing area of research, because of their importance in biomimetic studies of binuclear metalloproteins, their interesting catalytic properties, their ability to stabilize unusual oxidation states and mixed-valence compounds, and the possibilities for magnetic interaction between the two metal ions, leading to the design of molecular magnetic materials. − The Robson-type ligands ( I − III , Figure ) derived from 4-substituted 2,6-diformylphenol (or analogous ketones) and a variety of α,ω-diamines are among the most accessible dicompartmental compounds. , The essentially planar structures of the ligands provide efficient pathways for metal−metal interactions through bridging phenolic oxygen atoms. The planarity of the complexes, however, results in the relatively low solubilities of these compounds, , limiting their possible applications (although the solubilities of the complexes can be increased by varying the substituents in the 4-positions of the phenolic rings 4,7,8 ).…”

Section: Introductionmentioning

confidence: 99%

Dicompartmental Ligands with Hexa- and Tetradentate Coordination Sites: One-Step Synthesis of Ligands and Metal Complexes and Their X-ray Structure Analysis

1998

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Examples of interesting ligands previously requiring lengthy synthetic procedures have been prepared by onestep routes, opening the way to more extensive studies of their complexes and to possible applications. New dicompartmental ligands bearing picolyl pendant arms on the amine nitrogen donors have been synthesized, via the Mannich condensation, from 5-substituted salicylaldehydes, formaldehyde, and N,N′-bis(2-pyridylmethyl)-1,2-diaminoethane. The protonated acyclic ligand salt, two mononuclear complexes of a macrocyclic ligand with a second compartment featuring a Schiff base, and one of the decomposition products resulting from a retro-Mannich reaction have been structurally characterized. The ligand salt (L1b) has an extended conformation with the ethylenediamine fragment displaying the trans configuration, very different from that of the corresponding closed-site macrocyclic complexes NiH 2 (L2b) 2+ and ZnH 2 (L2b) 2+ . The mononuclear macrocyclic complex NiH 2 -(L2b) 2+ has a much smaller ligand twist than the corresponcing Zn(II) complex. The degree of ligand distortion is correlated with the M-N bond length between the metal ions and the pyridine nitrogens; longer M-N bonds cause the pyridine rings to tilt and twist the phenolic rings out of the main ligand plane. The ability of the macrocyclic ligand L2b to accommodate a second metal ion has been demonstrated by successful synthesis of dinuclear complexes. The free carbonyl groups of the open-site ligand were transformed into oxime groups, and the corresponding dinuclear bis(nickel) complex has been prepared. Acetal formation by the free carbonyl groups of ligand and retro-Mannich rearrangements are found to be possible pathways for the decomposition of this family of dicompartmental ligands.

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Intramolecular ferromagnetic interactions in polynuclear metal complexes

Cited by 121 publications

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Organic Spin Clusters: Ferromagnetic Spin Coupling through a Biphenyl Unit in Polyarylmethyl Tri-, Penta-, Hepta-, and Hexadecaradicals

Organic Spin Clusters: Ferromagnetic Spin Coupling through a Biphenyl Unit in Polyarylmethyl Tri-, Penta-, Hepta-, and Hexadecaradicals

Migratory Transmetalation in Diphenoxo-Bridged Cu^IIM^II Complexes of a Dinucleating Macrocycle with N(amine)₂O₂ and N(imine)₂O₂ Metal-Binding Sites

Dicompartmental Ligands with Hexa- and Tetradentate Coordination Sites: One-Step Synthesis of Ligands and Metal Complexes and Their X-ray Structure Analysis

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Intramolecular ferromagnetic interactions in polynuclear metal complexes

Cited by 121 publications

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Organic Spin Clusters: Ferromagnetic Spin Coupling through a Biphenyl Unit in Polyarylmethyl Tri-, Penta-, Hepta-, and Hexadecaradicals

Organic Spin Clusters: Ferromagnetic Spin Coupling through a Biphenyl Unit in Polyarylmethyl Tri-, Penta-, Hepta-, and Hexadecaradicals

Migratory Transmetalation in Diphenoxo-Bridged CuIIMII Complexes of a Dinucleating Macrocycle with N(amine)2O2 and N(imine)2O2 Metal-Binding Sites

Dicompartmental Ligands with Hexa- and Tetradentate Coordination Sites: One-Step Synthesis of Ligands and Metal Complexes and Their X-ray Structure Analysis

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Migratory Transmetalation in Diphenoxo-Bridged Cu^IIM^II Complexes of a Dinucleating Macrocycle with N(amine)₂O₂ and N(imine)₂O₂ Metal-Binding Sites