Electronic and Structural Properties of the Double Cubane Iron-Sulfur Cluster

The double-cubane cluster (DCC) refers to an [Fe8S9] iron-sulfur complex that is otherwise only known to exist in nitrogenases. Containing a bridging µ2-S ligand, the DCC in the DCC-containing protein (DCCP) is covalently linked to the protein scaffold via six coordinating cysteine residues. In this study, the nature of spin coupling and the effect of spin states on the cluster’s geometry are investigated computationally. Using density functional theory (DFT) and a broken symmetry (BS) approach to study the electronic ground state of the system, we computed the exchange interaction between the spin-coupled spins of the four FeFe dimers contained in the DCC. This treatment yields results that are in excellent agreement with both computed and experimentally determined exchange parameters for analogously coupled di-iron complexes. Hybrid quantum mechanical (QM)/molecular mechanical (MM) geometry optimizations show that cubane cluster A closest to charged amino acid side chains (Arg312, Glu140, Lys146) is less compact than cluster B, indicating that electrons of the same spin in a charged environment seek maximum separation. Overall, this study provides the community with a fundamental reference for subsequent studies of DCCP, as well as for investigations of other [Fe8S9]-containing enzymes.

Tetranuclear copper(ii) cubane complexes derived from self-assembled 1,3-dimethyl-5-(o-phenolate-azo)-6-aminouracil: structures, non-covalent interactions and magnetic property

A new doubly opened 4 + 2 Cu4O4 cubane cluster exhibits strong antiferromagnetic exchange coupling with J1 = −110.1 cm−1, and J2 = −27.1 cm−1.

Synthesis of Novel Tetra(µ3-Methoxo) Bridged with [Cu(II)-O-Cd(II)] Double-Open-Cubane Cluster: XRD/HSA-Interactions, Spectral and Oxidizing Properties

A new double-open-cubane core Cd(II)-O-Cu(II) bimetallic ligand mixed cluster of type [Cl2Cu4Cd2(NNO)6(NN)2(NO3)2].CH3CN was made available in EtOH/CH3CN solution. The 1-hydroxymethyl-3,5-dimethylpyrazole (NNOH) and 3,5-dimethylpyrazole (NNH) act as N,O-polydentate anion ligands in coordinating the Cu(II) and Cd(II) centers. The structure of the cluster in the solid state was proved by XRD study and confirmed in the liquid state by UV-vis analysis. The XRD result supported the construction of two octahedral and one square pyramid geometries types around the four Cu(II) centers and only octahedral geometry around Cd(II) two centers. Interestingly, NNOH ligand acts as a tetra-µ3-oxo and tri-µ2-oxo ligand; meanwhile, the N-N in NNH acts as classical bidentate anion/neutral ligands. The interactions in the lattice were detected experimentally by the XRD-packing result and computed via Hirschfeld surface analysis (HSA). The UV-vis., FT-IR and Energy Dispersive X-ray (EDX), supported the desired double-open cubane cluster composition. The oxidation potential of the desired cluster was evaluated using a 3,5-DTB-catechol 3,5-DTB-quinone as a catecholase model reaction.

Synthesis, characterization and crystal structure of a novel tetranuclear Co(II) cubane cluster

A new tetranuclear Co(II) cubane cluster 1, [Co4(L1)4(L2)4]·4CH3CH2OH (HL1 = 2-Methylquinolin-8-ol, HL2 = t-Bu-COOH), has been synthesized and characterized by X-ray single crystal diffraction, FT-IR, TG/DSC, and elementary analysis. The data reveals that it has a very interesting structural motif consisting of a [Co4O4] core in the form of a cube with the Co and O occupying opposite corners. In the crystal structure of complex 1, the molecules are linked by intramolecular C−H···O hydrogen bonding interactions and Van der Waals forces, forming a three-dimensional network structure. Crystal data for complex 1: C60H68Co4N4O12, triclinic, space group P-1 (no. 2), with a = 12.0644(4), b = 12.0996(3), c = 20.2858(7) Å, α = 92.005(3)o, β = 92.182(3)°, γ = 97.943(3)°, Z = 2, V = 2928.25(16) Å3, T = 293 K, μ(MoKα) = 1.178 mm-1, Dcalc = 1.444 g/cm3, 16737 reflections measured (3.00° ≤ θ ≤ 28.53°), 9010 unique (Rint = 0.024, Rsigma = 0.0574) which were used in all calculations. The final R1 was 0.039 (I≥2σ(I)) and wR2 was 0.090 (all data).

ATP-dependent substrate reduction at an [Fe8S9] double-cubane cluster

Chemically demanding reductive conversions in biology, such as the reduction of dinitrogen to ammonia or the Birch-type reduction of aromatic compounds, depend on Fe/S-cluster–containing ATPases. These reductions are typically catalyzed by two-component systems, in which an Fe/S-cluster–containing ATPase energizes an electron to reduce a metal site on the acceptor protein that drives the reductive reaction. Here, we show a two-component system featuring a double-cubane [Fe8S9]-cluster [{Fe4S4(SCys)3}2(μ2-S)]. The double-cubane–cluster-containing enzyme is capable of reducing small molecules, such as acetylene (C2H2), azide (N3−), and hydrazine (N2H4). We thus present a class of metalloenzymes akin in fold, metal clusters, and reactivity to nitrogenases.