Interaction between heterobinuclear molecules and nature of the ground spin state in oximato-bridged [CuIIMII]2 bis-binuclear complexes (M=Cu, Ni, Mn): crystal structure of [Cu(pdmg)Ni(Me3N3)(EtOH)](ClO4)2
Abstract: Two new heterobimetallic complexes [Cu(pdmg)Ni(Me 3 N 3 )(CH 3 CH 2 OH)](ClO 4 ) 2 ( 2 ) and [Cu(pdmg)Mn(bipy) 2 ](ClO 4 ) 2 · H 2 O ( 3 ) (H 2 pdmg=3,9-dimethyl-4,8-diazaundeca-3,8-diene-2,10-dione dioxime; Me 3 N 3 =2,4,4-trimethyl-1,5,9-triazacyclododeca-1-ene; bipy=2,2′-bipyridyl) have been prepared and characterized. The structure of 2 has been determined by single-crystal X-ray diffraction methods. It consists of [Cu(pdmg)Ni(Me 3 N 3 )(CH 3 CH 2 OH)] 2+ cations and non-coordinated perchlorate anions. The [Cu(pdmg)(CH 3 CH 2 OH)] complex coordinates to the [Ni(Me 3 N 3 )] 2+ fragment to afford the binuclear unit doubly-bridged by oximato groups in cis arrangement. The coordination geometry around the copper atom is square-pyramidal, whereas the nickel atom exhibits a trigonal-bipyramidal surrounding. The intramolecular Cu–Ni distance is 3.810(6) A. In the crystal, two [Cu II Ni II ] dimeric units are related through an inversion center, giving rise to a bis-binuclear entity with a relatively short intermolecular Cu–Cu separation of 4.175(6) A. Variable-temperature magnetic susceptibility measurements (2.0–300 K) for 2 correspond to an almost isolated Cu(II)Ni(II) pair with an intrapair interaction parameter J =−143.6(2) cm −1 . However, the EPR spectrum at 4.2 K is that of a triplet spin state arising from the interaction between the two doublet spin states within the [Cu II Ni II ] 2 bis-binuclear entity. The magnetic properties of 3 unambiguously reveal the bis-binuclear nature of this compound, as is the case for the related homometallic complex [Cu(pdmg)Cu(bipy)(H 2 O) 2 ](ClO 4 ) 2 · H 2 O ( 1 ). The intra- ( J ) and interpair ( j ) interaction parameters for 3 , as deduced from the analysis of its magnetic susceptibility data in the temperature range 2.0–300 K, are −50.9(2) and 1.50(2) cm −1 , respectively. The field dependence of the magnetization of 3 at 2.0 K corresponds to that of a nonet state arising from the interaction between two quintuplet spin states within the [Cu II Mn II ] 2 bis-binuclear entity. The interaction between the heterobinuclear Cu(II)Mn(II) molecules and its influence on the nature of the ground spin state for 3 are analyzed and discussed in the framework of a spin polarization scheme.
Abstract: The strategy of using ‘metal oximates’ building blocks as ligands to synthesize various homo- and hetero-metal paramagnetic complexes is reviewed. The modular approach with ‘metal-complexes’, in this case ‘metal-oximates’, as ligands enables the synthesis of symmetrical, asymmetrical, and linear complexes, viz. MAMB, MAMBMA, MAMBMBMA (MA, MB being two different metal ions). Even the synthesis of asymmetric heterotrinuclear complexes with MAMBMC cores and of MA(μ3-O)2MB butterfly cores has been achieved. This article is focused on such exchange coupled polymetallic, both homo- and hetero-metallic, systems containing the bridging core MNOM′ with an aim to delineate the exchange mechanism through the bridging oximates. The uniqueness of oximates providing diatomic NO-bridging is demonstrated by several series of isostructural complexes with different terminal metal ions like Fe(III), Mn(III), Mn(IV) and Cr(III). Such isostructural series are not available for any other bridging ligands. A qualitative rationale for the trend and nature of exchange interactions between the spin carriers has been provided. This article confirms the essentially σ nature of the exchange interaction transmitted through the diatomic NO-bridging ligand and the applicability of Goodenough–Kanamori rules, in general, to predict the nature of exchange interactions for different heterometal compounds. The π-conjugated system of the oxime ligand, delocalized over the whole bridging groups and perpendicular to the plane of the oxime ligand, appears to play an important role in the antiferromagnetic interaction between the terminal metal ions, separated by as much as ∼7 A. A comparison of the complexes MAMBMA containing a diamagnetic central ion (MB) clearly indicates the participation of the central metal ion in the transmission of the antiferromagnetic exchange interaction between the terminal paramagnetic MA ions. Competing exchange interactions, or spin frustration in the general sense of the term, in polynuclear complexes may lead to ground-state variability. This type of variable ground-state has been observed for several complexes. The strategy of irregular spin-state structure resulting from a particular spin topology has been found to be more effective, as expected, in obtaining ‘high spin’ molecules than the common strategy of obtaining ferromagnetically coupled systems through involvement of symmetry-related strict orthogonality of the magnetic orbitals of the interacting metal centers. Of particular interest for molecular magnetism is the small but significant effect of bridging ligands like carboxylato anions for cooperation with the ancillary ligand, viz. the oxime ligands, to build up high-nuclearity metal clusters.
TL;DR: The ligand 1,4,7-tris(acetophenoneoxime)-1,4-7-triazacyclononane (H(3)L) has been synthesized and its coordination properties toward Cu, Ni, Co, and Mn(II) in the presence of air have been investigated.
Abstract: The ligand 1,4,7-tris(acetophenoneoxime)-1,4,7-triazacyclononane (H(3)L) has been synthesized and its coordination properties toward Cu(II), Ni(II), Co(II), and Mn(II) in the presence of air have been investigated. Copper(II) yields a mononuclear complex, [Cu(H(2)L)](ClO(4)) (1), cobalt(II) and manganese(II) ions yield mixed-valence Co(III)(2)Co(II) (2a) and Mn(II)(2)Mn(III) (4) complexes, whereas nickel(II) produces a tetranuclear [Ni(4)(HL)(3)](2+) (3) complex. The complexes have been structurally, magnetochemically, and spectroscopically characterized. Complex 3, a planar trigonal-shaped tetranuclear Ni(II) species, exhibits irregular spin-ladder. Variable-temperature (2-290 K) magnetic susceptibility analysis of 3 demonstrates antiferromagnetic exchange interactions (J = -13.4 cm(-1)) between the neighboring Ni(II) ions, which lead to the ground-state S(t) = 2.0 owing to the topology of the spin-carriers in 3. A bulk ferromaganetic interaction (J = +2 cm(-1)) is prevailing between the neighboring high-spin Mn(II) and high-spin Mn(III) ions leading to a ground state of S(t) = 7.0 for 4. The large ground-state spin value of S(t) = 7.0 has been confirmed by magnetization measurements at applied magnetic fields of 1, 4 and 7 T. A bridging monomethyl carbonato ligand formation occurs through an efficient CO(2) uptake from air in methanolic solutions containing a base in the case of complex 4.
TL;DR: A wattle-type heteropolynuclear complex, which represents the first system with macrocyclic oxamido and alternate azido bridges, forming a one-dimensional chain structure, has been synthesized and characterized by a low temperature magnetic study.
Abstract: A wattle-type heteropolynuclear complex [(CuL)Mn(N3)2]n (1) (H2L = 2,3-dioxo-5,6:15,16-dibenzo-1,4,8,13-tetraazacyclo-pentadeca-7,13-diene), which represents the first system with macrocyclic oxamido and alternate azido bridges, forming a one-dimensional chain structure, has been synthesized and characterized by a low temperature magnetic study. The chains are stacked with interchain hydrogen and lead to the structure of a three-dimensional network.
TL;DR: Three trinuclear complexes based on (pyridine-2-aldoximato)nickel(II) units are described and display antiferromagnetic exchange coupling of the neighbouring metal centers, while weak ferromagnetic spin exchange between the adjacent Ni II and Cr III ions in is observed.
Abstract: Three trinuclear complexes, NiIIMnIIINiII1, NiIICrIIINiII2 and NiII33 based on (pyridine-2-aldoximato)nickel(II) units are described. Two of them, 1 and 2, contain metal-centers in linear arrangement, as is revealed by X-ray diffraction. Complex 3 is a homonuclear complex in which the three nickel(II) centers are disposed in a triangular fashion. The compounds were characterized by various physical methods including cyclic voltammetric and variable-temperature (2–290 K) susceptibility measurements. Complexes 1 and 3 display antiferromagnetic exchange coupling of the neighbouring metal centers, while weak ferromagnetic spin exchange between the adjacent NiII and CrIII ions in 2 is observed. The experimental magnetic data were simulated by using appropriate models.
TL;DR: Heme-containing nitrite reductases bind and activate nitrite by a mechanism that is proposed to involve interactions with Brønsted acidic residues in the secondary coordination sphere, to model this functionality using synthetic platforms that incorporate a Lewis acidic site.
Abstract: Heme-containing nitrite reductases bind and activate nitrite by a mechanism that is proposed to involve interactions with Bronsted acidic residues in the secondary coordination sphere. To model this functionality using synthetic platforms that incorporate a Lewis acidic site, heterobimetallic CoMg complexes supported by diimine–dioxime ligands are described. The neutral (μ-NO2)CoMg species 3 is synthesized from the [(μ-OAc)(Br)CoMg]+ complex 1 by a sequence of one-electron reduction and ligand substitution reactions. Data are presented for a redox series of nitrite adducts, featuring a conserved μ-(η1-N:η1-O)-NO2 motif, derived from this synthon. Conditions are identified for the proton-induced N–O bond heterolysis of bound NO2– in the most reduced member of this series, affording the [(NO)(Cl)CoMg(H2O)]+ complex 6. Reduction of this complex followed by protonation leads to the evolution of free N2O. On the basis of these stoichiometric reactivity studies, the competence of complex 1 as a NO2– reduction c...
Abstract: An extension of Furnas's method is described. The variation of intensity of an axial reflection as the crystal is rotated about the goniometer axis is used to give a curve of relative transmission T against azimuthal angle ϕ for the corresponding reciprocal lattice level. Transmission coefficients for any general reflexion hkl are then given approximately by T(hkl) = [T(ϕinc) + T(ϕret)]/2 where ϕinc and ϕret are the azimuthal angles of the incident and reflected beams. Equations are derived for (ϕinc and ϕret and the accuracy of the method is discussed.
Abstract: Publisher Summary The field of heterobimetallic systems has developed tremendously over the past several years particularly in relation to the synthesis of molecular-based magnets This chapter reviews the advancements in the field of bimetallic magnets The chapter also discusses some key concepts in molecular magnetism—as spin delocalization, spin polarization—and the interaction between two spin carriers Several compounds are presented in order of increasing nuclearity and dimensionality The chapter focuses on the bridges that have allowed the design of molecular-based magnets These bridges are oxamato, oxamido, oxalato, dithiooxalato, oximato, and cyano Molecular magnetism has emerged as a novel field of research over the past several years This field concerns the chemistry and the physics of open-shell molecules and molecular assemblies containing open-shell units Among all molecules and molecular assemblies relevant to molecular magnetism, those containing two (or possibly more) kinds of metal ions have played a particularly important role