Iron–sulfur clusters and their electronic and magnetic properties

Iron–sulfur clusters of diverse nuclearities constitute the active sites of a large and prominent family of metalloproteins which play essential roles in all living organisms, such as in electron transfer chains, reduction catalysis, photosynthesis, the respiratory chain and nitrogen fixation. This review is devoted to the presentation of the current state of understanding of their electronic and magnetic properties, which is here derived from their Mössbauer, EPR and ENDOR spectroscopic properties. These techniques constitute fine tools for characterization and provide knowledge of the different oxidation states of these proteins, although our interest here will be mainly centered on the [4Fe–4S*]ⁿ⁺ clusters (with n=1–3). A qualitative physical model involving the competing magnetic interactions in these clusters is discussed. Moreover, this article contains new developments on two more specialized subjects:

• 1.some quantitative consequences of an already published theory of the g-tensors of [4Fe–4S*]ⁿ⁺ clusters (n=1,3) will be derived in Section 3;
• 2.a model permitting the rationalization, from very simple ingredients and formulae, of the redox potentials of a whole set of known synthetic redox clusters (with 1, 2, 3, 4 and 6 iron atoms) will be presented in the final Section 6.

     

Syntheses,structures and magnetic properties of isonicotinate-bridged heterometallic Ln(III)–Cu(II) coordination polymers

The heterometallic Ln(III)–Cu(II) coordination polymers [CuLn₂(IN)₈(H₂O)₄] _n (IN?=?isonicotinate, Ln?=?Gd (1), Dy (2), Er(3)) have been synthesized by hydrothermal reactions and characterized by elemental analysis, IR and single crystal X-ray diffraction. The compounds are isomorphous and crystallize in monoclinic space group P2₁/c, adopting a one-dimensional chain structure with alternately arranged [Ln₂(IN)₆(H₂O)₄] and [Cu(IN)₂] building blocks bridged by isonicotinates. Temperature-dependent magnetic susceptibility for complex 1 was studied, and a very weak ferromagnetic interaction between metal ions was observed.     

Syntheses, crystal structures, and magnetic properties of four one-dimensional metal–nitroxide coordination polymers linked by flexible dicarboxylate anions

Four new one-dimensional coordination polymers [Co(IM4Py)₂(adi)(H₂O)₂] _n , [Zn(IM4Py)₂(adi)(H₂O)₂] _n , [Cd(IM4Py)₂(adi)(H₂O)₂] _n , and [Ni(IM4Py)₂(glu)(H₂O)₂] _n (IM4Py = 2-(4′-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl, adi = adipate anion and glu = glutarate anion) were synthesized and structurally characterized. The single-crystal X-ray analyses indicate that all four complexes crystallize in neutral one-dimensional chains in which the nitroxide–metal–nitroxide units are bridged by the flexible dicarboxylate anions. The adipate anions adopt the anti/gauche/anti and anti/anti/anti conformations in the Co(II), Zn(II), and Cd(II) complexes, while the glutarate anions only possess the anti/anti conformation in the Ni(II) complex. The magnetic properties of the Co(II) and Ni(II) complexes show the occurrence of weak antiferromagnetic interactions between the metal atoms and the nitroxide radicals.     

Synthesis,structures and luminescent properties of 4d–4f heterometallic coordination frameworks based on lanthanide oxalate substructures with nicotinate bridging ligands

Four transition–lanthanide metal–organic coordination polymers, namely [Ag₂Ln(nic)₄(H₂O)₄ · (ClO₄) · H₂O] [Ln = Eu (1), Gd (2)] and [AgLn(nic)₂(ox)_0.5(H₂O)₂ · (ClO₄) · H₂O] [Ln = Tb (3), Yb (4)] (nic = nicotinate; ox = oxalate) have been synthesized by the hydrothermal reactions of 4d and 4f metal salts with N-/O-donor ligands. The isostructural complexes 1 and 2 exhibit novel 2D wave-like heterometallic layers constructed by the assembly of 1D chains of lanthanide–carboxylate with Ag(nic)₂ subunits. Complexes 3 and 4 show another unusual 3D heterometallic coordination framework constructed from 2D lanthanide–oxalate layers and pillar-like Ag(nic)₂ subunits. Furthermore, the luminescent properties of complexes 1 and 3 were studied.     

Synthesis,structures and magnetic properties of four 3D heterometallic cobalt(II)–barium(II) coordination polymers

Four heterometallic complexes, namely {[CoBa(2,5-pdc)₂(H₂O)₃]_n·2nH₂O} (1), [CoBa(2,5-pdc)₂(H₂O)₄]_n (2), [CoBa(2,5-pdc)₂(H₂O)₅]_n (3) and [CoBa₂(2,5-pdc)₃(μ₂-H₂O)₂(H₂O)₄]_n (4) (2,5-H₂pdc?=?pyridine-2,5-dicarboxylic acid), have been hydrothermally synthesized and characterized both structurally and magnetically. All four complexes exhibit 3D frameworks, in which the Co(II) centers are chelated by pyridine nitrogen and carboxyl oxygen atoms in a five-membered ring. The Ba(II) centers are chelated and bridged by carboxyl oxygen atoms to extend the structures into 3D frameworks. The networks of the complexes can be controlled via rationally choosing the appropriate ligand and tuning the ratio of the two types of metal centers. The magnetic properties of complexes 1, 2 and 4 have been investigated from 2 to 300 K.     

Two new lanthanide–radical complexes: synthesis,structure, and magnetic properties

Two new lanthanide–radical complexes, [Tb(hfac)₃(EtVNIT)₂] (1) and [Dy(hfac)₃(EtVNIT)₂] (2) (EtVNIT?=?2-(4′-ethoxy-3′-methoxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, hfac?=?1,1,1,5,5,5-hexafluoroacetylacetonate), were synthesized; both display radical–Ln(III)–radical (Ln=Tb (1), Dy (2)) tri-spin structures. Magnetic studies reveal that interactions between the lanthanide ions and radicals are ferromagnetic.     

Synthesis and crystal structures of coordination polymers,networks and complexes of an adamantane shaped phosphorus–nitrogen cage ligand and cuprous chloride

Reactions of cuprous chloride with the phosphorus–nitrogen cage ligand 2,4,6,8,9,10-hexamethyl-2,4,6,8,9,10-hexaaza-1,3,5,7-tetraphosphaadamantane, P₄(NCH₃)₆, in acetonitrile form distinct solids depending on the ligand-to-metal ratio. Three structurally characterized compounds include: a solvated 3-D network of formula [P₄(NCH₃)₆]₂(CuCl)₃(CH₃CN)₂; a “ladder-type” polymer {[μ₂-P₄(NCH₃)₆]₂(CuCl)₂}_∞; and a monomeric complex [P₄(NCH₃)₆]₂CuCl. Thermal decomposition of the solvated network results in formation of two more materials [P₄(NCH₃)₆]₂(CuCl)₃, and [P₄(NCH₃)₆](CuCl)₂ that are not isolated from solution reactions. The variety of products isolated based solely on ligand-to-metal ratio suggest that this system participates in solution equilibria common to many phosphorus(III) ligands and multiple solubility equilibria.     

Synthesis,structures and magnetic properties of two 2D → 3D entangled Cobalt(II) coordination polymers

Two Co(II) coordination polymers, namely Co(HBTC)(4-bpdb)·H₂O (1) and Co(HBTC)(3-bpdb)·H₂O (2) (H₃BTC = 1,3,5-benzenetricarboxylic acid, 4-bpdb = 1,4-bis-(4-pyridyl)-2,3-diaza-1,3-butadiene, 3-bpdb = 1,4-bis(3-pyridyl)-2,3-diaza-1,3- butadiene), have been hydrothermally synthesized and characterized both structurally and magnetically. Compound 1 exhibits a (2D → 3D) polythreaded architecture. It is assembled from HBTC^2? ligands to form a 2D puckered (4,4) layer plus 4-bpdb ligands which are orientated above and below each layer. The structure of compound 2 consists of a 2D (3,5) wavelike sheet constructed from HBTC^2? anions and 3-bpdb spacers. The uncoordinated carboxyl groups of the HBTC^2? ligands protrude from both sides of the wavelike sheet to form a 2D → 3D interdigitated motif. The magnetic properties of both compounds are also investigated, indicating antiferromagnetic interactions between the adjacent metal centers.     

Sandwich heterometallic coordination polymers consisting of copper-cluster pillars and layered networks of {Ln6} wheels: synthesis,structures, spectroscopic properties and Judd–Ofelt analysis

Transition Metal Chemistry - Two novel 3-D Ln(III)–Cu(I) heterometallic coordination polymers, [Ln2Cu2(L3)4(C2O4)2]·H2O (Ln?=?Sm, Eu; HL3?=?5-aminonicotinic...     

pH-Controlled assembly of two POM-based inorganic–organic hybrid copper coordination polymers: synthesis,structures and properties

Transition Metal Chemistry - Two POM-based copper coordination polymers constituted by Keggin-type polyoxometalates (POMs), [Cu2 (SiW12O40)2 (Fbtx)3 (H2O)4]n (1) and {[Cu2 (SiW12O40) (Fbtx)2...     

Crystal structures and magnetic properties of three cobalt(II)–organic frameworks with nanoscale channels

Three cobalt(II) coordination polymers, {[Co(nip)(4,4′-bpy)] · 3H₂O} _n (1), [Co(nip)(bpe)] _n (2), and [Co(nip)(bpp)(H₂O)] _n (3), were hydrothermally synthesized by the reaction of cobalt nitrate hexahydrate and nip with 4,4′-bpy, bpe, and bpp [nip = 5-nitro-1,3-benzenedicarboxylato, 4,4′-bpy = 4,4′-bipyridine, bpe = 1,2-bis(4-pyridyl)ethane, bpp = 1,3-bis(4-pyridyl)propane], respectively. Co(II) displays different coordination in the three complexes, resulting in different structures with nanoscale channels. Compounds 1 and 2 form 2-D layer structures, but 3 has a two-fold interpenetrated 3-D framework. The magnetic properties associated with their crystal structures were investigated.     

Synthesis,structure, and magnetic properties of lanthanide ferrocenoylacetonates with nitrate and 2,2′-bipyridine ligands

Ferrocenoylacetonate complexes of several lanthanides, [Ln(fca)₂(NO₃)(bpy)]·nMeC₆H₅ (Ln = Sm (1), Dy (3), Er (4), Yb (5), n = 1; Eu (2), n = 0.5; fca = FcC(O)CHC(O)Me; bpy = 2,2′-bipyridine), were synthesized and characterized by X-ray single-crystal analysis. Complexes 1, 4, and 5 are isostructural; 2 has a similar molecular structure with cis-disposition of fca ligands. The molecular structure of 3 is different, with trans-disposition of the fca ligands. Crystal lattices of the complexes are stabilized by π-stacking interactions. The Ln³⁺ ions in the complexes are eight-coordinate. According to mass spectroscopic data, the complexes are unstable in the gas phase. Magnetic properties of 2 and 4 were studied in a DC field; for 4, AC studies were also carried out. The values of spin-orbital parameters obtained using two estimation methods for 2 are in satisfactory agreement. Slow relaxation of the magnetization was found for the Er complex.     

Elastic properties and electronic structures of typical Al–Ce structures from first-principles calculations

The elastic property and electronic structure of three typical Al–Ce structures have been studied by means of first-principles calculations within GGA approximation. The optimized structural parameters for these precipitates agree very well with experimental data. The obtained negative cohesive energy and formation enthalpy show that all of these precipitates have strong structural stability. Elastic constants as well as other mechanical parameters such as bulk modulus B, shear modulus G, Young’s modulus E and Poisson’s ratio ν for these phases are computed and discussed. The calculated electronic densities of state and charge distribution show the covalent features of Ce–Ce and Al–Ce bonding in three phases, which reveals the underlying mechanism for the elastic properties of these Al–Ce structures.     

Synthesis and X-ray crystal structures of a series of 3d–4f lanthanide complexes: lanthanide(III)–copper(II) coordination polymers with 2,5-pyridinedicarboxylic acid ligand

A series of lanthanide–transition metal (Ln–M) complexes, namely, {[Ln₂Cu(pydc)₄(H₂O)₃]·H₂O} _n (Ln = Tb, Eu, Sm or Gd) (H₂pydc = 2,5-pyridinedicarboxylic acid) have been synthesized hydrothermally by self-assembly of the lanthanide ions, copper(II) ions and 2,5-pyridinedicarboxylic acid. All the complexes were characterized by physicochemical and spectroscopic methods; in addition, structural analyses revealed that all four complexes crystallized in monoclinic space group P2₁ /c. The molecular structure contains both Cu and Ln atoms, with pydc ligands bridging the four coordinate Cu(II) centers and eight coordinate lanthanide centers to form a 3-D net structure. Hence, copper is oxidized from Cu(I) to Cu(II) during the preparation. In addition, the thermogravimetric analysis of 1 is discussed. Contrary to expectations, compounds 1–3 show no photoluminescent properties. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

First principles study of the electronic and magnetic structures and bonding properties of UCoC2 ternary,characteristic of C–C units

The electronic structure of UCoC₂, a di-carbide with the C–C units is examined from ab initio with an assessment of the properties of chemical bonding. The energy–volume equation of state shows large anisotropy effects due to C–C alignment along tetragonal c-axis leading to high linear incompressibility. Relevant features of selective bonding of uranium and cobalt with carbon at two different Wyckoff sites and strong C–C interactions are remarkable. The vibrational frequencies for C⋯C stretching modes indicate closer behavior to aliphatic C–C rather than CC double bond. A ferromagnetic ground state is proposed from the calculations.     

Two isomorphous Mn(II) and Co(II) 5-amino-tetrazolate coordination polymers with magnetic Δ-chains: crystal structures and magnetic properties

Two Co(II) and Mn(II) coordination polymers, which have been synthesized under hydrothermal conditions, are isomorphous with magnetic Δ-chains containing trinuclear triangular [M(3)(μ(3)-OH)] clusters. The Δ-chains are bridged by isonicotinic spacers to generate a two-dimensional scalariform layer structure. Magnetic investigations indicate that Co(II) compound exhibits not only spin canting but also metamagnetic behaviors, while only spin-canted antiferromagnetic behaviors was observed in Mn(II) compound.     

Syntheses, structures and properties of two unusual silver-organic coordination networks: 1D→1D tubular intertwinement and existence of an infinite winding water chain

Two unusual metal-organic frameworks {[Ag(2)(Hbtc)(bpy)(2)]·(H(2)O)(2)}(n) (1), {[Ag(3)(btc)(bpy)(3)(H(2)O)]·(H(2)O)(7)}(n) (2) (H(3)btc = 1,2,3-benzenetricarboxylic acid, bpy = 4,4'-bipyridine) have been synthesized and characterized by single crystal X-ray diffraction. Complex 1 features an infinite 1D→1D tubular intertwinement network, while complex 2 exhibits a double ladder structure which contains rare winding water chains. Both infinite 1D→1D tubular chains in complex 1 and double ladder in 2 are mutually interconnected by hydrogen bonding and π···π stacking interactions into three-dimensional (3D) supramolecular networks. In addition, thermogravimetric analysis, powder X-ray diffraction (XRD), and photoluminescent behavior of the complexes have also been investigated.     

Synthesis and magnetic properties of an iminonitroxide-substituted phenolate–Cu complex

A new spin-chelate, iminonitroxide-substituted phenolate–copper complex (1), was designed and prepared. The structure of the complex 1 was considerably deviated from a square-planar geometry. The dihedral angle between the two planes defined by a set of copper, oxygen and nitrogen atoms was about 41°. The complex was found to have a relatively strong ferromagnetic interaction and a weaker antiferromagnetic interaction: J/k_B=+250 K and θ=−17 K using a three-spin model. The ferromagnetic interaction was assigned to the intramolecular interaction between the copper atom and the iminonitroxide. The antiferromagnetic interaction was assigned as an intermolecular interaction. These assignments were supported by susceptibility measurements for the diluted sample in polyvinyl chloride (PVC) film. The antiferromagnetic interaction was tentatively assigned due to the observed short intermolecular contacts between the C5 and O1 atoms or between the H5 and O1 atoms.     

Dipyridyl β-diketonate complexes and their use as metalloligands in the formation of mixed-metal coordination networks

The iron(III) and aluminium(III) complexes of 1,3-di(4-pyridyl)propane-1,3-dionato (dppd) and 1,3-di(3-pyridyl)propane-1,3-dionato (dmppd), [Fe(dppd)(3)] 1, [Fe(dmppd)(3)] 2, [Al(dppd)(3)] 3 and [Al(dmppd)(3)] 4 have been prepared. These complexes adopt molecular structures in which the metal centres contain distorted octahedral geometries. In contrast, the copper(II) and zinc(II) complexes [Cu(dppd)(2)] 5 and [Zn(dmppd)(2)] 6 both form polymeric structures in which coordination of the pyridyl groups into the axial positions of neighbouring metal centres links discrete square-planar complexes into two-dimensional networks. The europium complex [Eu(dmppd)(2)(H(2)O)(4)]Cl·2EtOH·0.5H(2)O 7 forms a structure containing discrete cations that are linked into sheets through hydrogen bonds, whereas the lanthanum complex [La(dmppd)(3)(H(2)O)]·2H(2)O 8 adopts a one-dimensional network structure, connected into sheets by hydrogen bonds. The iron complexes 1 and 2 act as metalloligands in reactions with silver(I) salts, with the nature of the product depending on the counter-ions present. Thus, the reaction between 1 and AgBF(4) gave [AgFe(dppd)(3)]BF(4)·DMSO 9, in which the silver centres link the metalloligands into discrete nanotubes, whereas reactions with AgPF(6) and AgSbF(6) gave [AgFe(dppd)(3)]PF(6)·3.28DMSO 10 and [AgFe(dppd)(3)]SbF(6)·1.25DMSO 11, in which the metalloligands are linked into sheets. In all three cases, only four of the six pyridyl groups present on the metalloligands are coordinated. The reaction between 2 and AgNO(3) gave [Ag(2)Fe(dmppd)(3)(ONO(2))]NO(3)·MeCN·CH(2)Cl(2)12. Compound 12 adopts a layer structure in which all pyridyl groups are coordinated to silver centres and, in addition, a nitrate ion bridges between two silver centres. A similar structure is adopted by [Ag(2)Fe(dmppd)(3)(O(2)CCF(3))]CF(3)CO(2)·2MeCN·0.25CH(2)Cl(2)13, with a bridging trifluoroacetate ion playing the same role as the nitrate ion in 12.