A correlation between isomer shifts of237Np Mössbauer spectra and coordination numbers of Np atoms in neptunyl(V) compounds

Five neptunyl(V) compounds were synthesized and studied by²³⁷Np Mössbauer spectroscopy. The isomer shifts (δ) of the Mössbauer spectra ranged from ?18.6 to ?19.1 mm/s for the compounds with Np atoms surrounded by 7 oxygen atoms (coordination number (CN) 7). On the other hand, the larger value of δ was obtained for the compound with CN 8. from the comparison of the present results with those reported on neptunyl(V) and (VI) compounds, it is concluded that there is a correlation between the δ and the CN for neptunyl(V) compounds, and the distribution of δ is narrower for neptunyl(V) compounds than that of neptunyl(VI) compounds.     

Theoretical study of the structural properties of plutonium(IV) and (VI) complexes

The structural properties of several plutonium(IV) and (VI) complexes have been examined in the gaseous and aqueous phases using Kohn-Sham density functional theory calculations with scalar relativistic effective core potentials and the polarizable continuum solvation model. The aquo and nitrate complexes of PuO(2)(2+) and Pu(4+) were considered in addition to the aquo-chloro complexes of PuO(2)(2+). The nitrate and chloro- complexes formed with triphenylphosphine oxide (TPPO) and tributylphosphate (TBP) respectively were also studied. The structural parameters of the plutonyl complexes were compared to their uranyl and neptunyl analogues. The bond lengths and vibrational frequencies of the plutonyl complexes can generally be computed with sufficient accuracy with the pure PBE density functional with shorter bond lengths being predicted by the B3LYP functional. The structural parameters of the [PuO(2)Cl(2)L(2)] systems formed with TPPO and TBP as well as the aqueous [PuO(2)Cl(2)(H(2)O)(3)] complex are matched to previous experimental results. Overall, the inclusion of ligands in the equatorial region results in significant changes in the stretching frequency of the plutonyl group. The structural features of the plutonyl (VI) systems are rather similar to those of their 5f(0) uranyl and 5f(1) neptunyl counterparts. For the Pu(IV) aquo and nitrate complexes, the average of the calculated Pu-OH(2) and Pu-O(nitrate) bond lengths are generally within 0.04 ? of the reported experimental values. Overall Kohn-Sham DFT can be used successfully in predicting the structures of this diverse set of Pu(VI) and Pu(IV) complexes.     

The first structural and spectroscopic characterization of a neptunyl polyoxometalate complex

The reaction between PW9O349- and NpO2+ has yielded the first structurally characterized neptunyl(V) polyoxometalate complex, [Na2(NpO2)2(A-PW9O34)2]14-. This complex is isostructural with the uranyl(VI) analogue, and there is also spectroscopic evidence for its existence in solution. The complex is readily extracted into toluene, and this may have significance in the sequestering and/or separation of the neptunyl ion in terms of nuclear waste management.     

Mössbauer spectroscopy of neptunyl species

Systematics of hyperfine parameters from ²³⁷Np Mössbauer resonance data of compounds with Np in a high formal charge state are discussed with respect to electronic structure properties. In neptunyl(VI) species, we find a linear correlation between the isomer shift and the strength of quadrupole interaction. Both scale linearly with the actinide-oxygen bond length, stressing the central role of this parameter. Some compounds show paramagnetic relaxation spectra which makes their analysis difficult. The hyperfine interactions are often not rotational symmetric indicating a deviation from the simple linear O-Np-O configuration. Mössbauer spectra of NpO₃·2H₂O reveal that this compound should be described as a neptunyl. A comparison of hyperfine parameter systematics indicates that the Np valence electron properties in Np(VII) species are basically similar to those in Np(VI) neptunyls.     

Synthesis,characterization, pharmacological,molecular modeling and antimicrobial activity evaluation of novel isomer quinoline derivatives

The structural and spectroscopic characteristics of the synthesized structurally novel compound 4-chloro-6-methylquinoline-2(1H)-one (4C6MQ) and its isomer 4-chloro-8-methylquinoline-2(1H)-one (4C8MQ) have been examined by means of experimental and computational quantum chemical methods like density functional theory (DFT). The crystal structure of the 4C6MQ compound has been brought to light by single-crystal x-ray diffraction (SCXRD) method which consists of two independent molecules (A and B) in the asymmetric unit with similar conformations. Both the isomer compounds are characterized spectroscopically by FTIR, FT-Raman, UV-Vis, and NMR spectrum and compared with DFT results. The geometries of the isomer compounds have been optimized by using DFT/B3LYP method with the 6-311G++(d,p) basis sets. From the optimized geometry of the compounds, geometric parameters (bond lengths, bond angles, and torsion angles); vibrational analysis; chemical shifts; and electronic absorption of the isomer compounds have been computed and compared with the experimental result. The detailed assignments of vibrational wave numbers have been prepared based on potential energy distribution (PED) which was carried out in the VEDA4 program. In addition, natural bonding orbital analysis, frontier molecular orbital, and molecular electrostatic potential have been explained theoretically. The in silico (absorption, distribution, metabolism, excretion and toxicity) studies were analyzed to identify the potential drug likeliness of the isomer compounds. The implications of the inhibitory activity of isomer compounds against DNA gyrase and lanosterol 14 α-demethylase enzyme by molecular docking are discussed. Further, the isomer compounds were screened for their antibacterial and antifungal activities.     

Structural and spectroscopic trends in actinyl iodates of uranium,neptunium, and plutonium

Two neptunyl(VI) iodates, NpO(2)(IO(3))(2)(H(2)O) (1) and NpO(2)(IO(3))(2).H(2)O (2), have been prepared from the aqueous reactions of Np(V) in HCl with KIO(4) or H(5)IO(6) at 180 degrees C and have been characterized by single crystal X-ray diffraction and Raman spectroscopy. Both compounds consist of two-dimensional arrangements of pentagonal bipyramidal [NpO(7)] polyhedra with axial neptunyl, NpO(2)(2+), dioxocations. In 1, the neptunium centers are bound in the equatorial plane by four bridging iodate anions and one terminal water molecule. The iodate anions link the [NpO(7)] units into corrugated sheets that interact with one another through intermolecular IO(3)(-)...IO(3)(-) interactions as also observed in UO(2)(IO(3))(2)(H(2)O). Compound 2 is isostructural with the recently reported PuO(2)(IO(3))(2).H(2)O, where oxygen atoms from bridging iodate anions occupy the five equatorial sites around the neptunyl moieties. The iodate anions occur as both mu(2)- and mu(3)-units and link the neptunyl polyhedra into sheets. Both types of iodate anions have their stereochemically active lone-pair of electrons aligned on one side of each layer creating a polar structure. Raman spectra of 1, UO(2)(IO(3))(2)(H(2)O), and PuO(2)(IO(3))(2).H(2)O show a sequential shift of the nu(1)(AnO(2)(2+)) stretch to lower wavenumber as the atomic number of the actinide is increased. Crystallographic data: 1, orthorhombic, space group Pcan, a = 7.684(2) A, b = 8.450(2) A, c = 12.493(3) A, Z = 4; 2, orthorhombic, space group Pna2(1), a = 7.314(1) A, b = 11.631(2) A, c = 9.449(2) A, Z = 4.     

Cyclic silylamides of vanadium, niobium, tantalum and hafnium. Crystal and molecular structures of spirocyclic tetraamides of V, CH3Nb and Hf

The spirocyclic silylamides M[(NR)₂SiMe₂]₂ (R = t-Bu: M = Hf (III), V (IV); R = SiMe₃: M = V (V), NbCl (VI), TaCl (VII)) have been prepared by reaction of the HfCl₄, VCl₄, NbCl₅ and TaCl₅, respectively, with Me₂Si[N(Li)R]₂. Methylation of VI and VII with MeLi yields the respective NbCH₃ and TaCH₃ derivatives (VIII and IX). The effective magnetic moments of IV and V are 1.67 and 1.66 μ_B respectively. Infrared and Raman spectra are given, and the ¹H, ¹³C and ²⁹Si chemical shifts for the diamagnetic compounds are reported. Single-crystal X-ray studies have been performed on III, IV and VIII. The structures of III and IV possess distorted tetrahedral symmetry (D_2d), with mean M---N distance of 2.030(4) and 1.853(5) Å, respectively. Distorted trigonal-bipyramidal coordination with an equatorial methyl group is found for each Nb atom of the two crystallographically independent molecules of VIII. Mean Nb---C, Nb---N (equatorial) and Nb---N (axial) bond lengths are 2.218(9), 1.997(4) and 2.026(5) Å, respectively.     

A comparison of neptunyl(V) and neptunyl(VI) solution coordination: the stability of cation-cation interactions

The solution coordination environments of pentavalent and hexavalent Np are studied by high-energy X-ray scattering. Np5+ and Np6+ both exist as the neptunyl moiety coordinated with five equatorial waters at Np-O distances of 2.46(2) and 2.37(2) A, respectively. NpO2(2+) also has a second coordination sphere of 6-10 waters at 4.37(3) A. The NpO2+ scattering is complicated by the presence of scattering at about 4.2 A that is attributed to Np-Np cation-cation interactions. The analysis of changing intensity of this peak as a function of Np concentration is used to determine a stability constant of Keq=0.74(9) M(-1) for the dimeric complex.     

Systematic DFT study of gas phase and solvated uranyl and neptunyl complexes [AnO2X4]n (An = U, Np; X = F, Cl, OH, n = -2; X = H2O, n = +2)

The six-valent uranyl and neptunyl complexes [An(VI)O2X4]n (An = U, Np; X = F, Cl, OH, n = -2; X = H2O, n = +2) have been studied within the framework of density functional theory. The relative stabilities of the cis and trans isomers, structural properties, charge distribution, and ligand binding energies have been determined using the modified Perdew-Burke-Ernzerhof functional at the all-electron scalar relativistic level. Uranyl and neptunyl complexes with different ligands have been compared in a systematic fashion, demonstrating close similarity of these actinides in oxidation state VI. In addition, the effect of an aqueous solution has been taken into account with the polarizable continuum model COSMO. Computed averaged ligand binding energies permit one to rationalize the observed different stabilities of the title species in aqueous media.     

Synthesis, structure, and infrared spectroscopy of the first Np5+ neptunyl silicates, Li6(NpO2)4(H2Si2O7)(HSiO4)2(H2O)4 and K3(NpO2)3(Si2O7)

Two Np(5+) silicates, Li(6)(NpO(2))(4)(H(2)Si(2)O(7))(HSiO(4))(2)(H(2)O)(4) (LiNpSi1) and K(3)(NpO(2))(3)(SiO(3)OH)(2) (KNpSi1), were synthesized by hydrothermal methods. The crystal structures were determined using direct methods and refined on the basis of F(2) for all unique data collected with Mo Kalpha radation and an APEX II CCD detector. LiNpSi1 crystallizes in orthorhombic space group Pnma with a =13.189(6) A, b = 7.917(3) A, c = 10.708(5) A, V = 1118.1(8) A3, and Z = 2. KNpSi1 is hexagonal, P62m, a = 9.734(1) A, c = 3.8817(7) A, V = 318.50(8) A3, and Z = 1. LiNpSi1 contains chains of edge-sharing neptunyl pentagonal bipyramids linked into two-dimensional sheets through direct linkages between the neptunyl polyhedra and the vertex sharing of the silicate tetrahedra. The structure contains both sorosilicate and nesosilicate units, resulting in a new complex neptunyl silicate sheet. KNpSi1 contains edge-sharing neptunyl square bipyramids linked into a framework structure through the sharing of vertices with the silicate tetrahedra. The neptunyl silicate framework contains channels approximately 6.0 A in diameter. These structures exhibit significant departures from other reported Np(5+) and U(6+) compounds and represent the first reported Np(5+) silicate structures.     

Electronic spectra and excited states of neptunyl and its [NpO2Cl4]2- complex

Electronic states and spectra of NpO(2)(2+) and NpO(2)Cl(4)(2-) with a Np 5f(1) ground-state configuration, related to low-lying 5f-5f and ligand-to-metal charge-transfer (CT) transitions, are investigated, using restricted-active-space perturbation theory (RASPT2) with spin-orbit coupling. Restrictions on the antibonding orbital occupations have little influence on the 5f-5f transition energies, but an important impact on the CT states with an open bonding orbital shell. The present calculations provide significant improvement over previous literature results. The assignment of the experimental electronic spectra of Cs(2)NpO(2)Cl(4) is refined, based on our calculations of NpO(2)Cl(4)(2-). Assignments on the basis of bare NpO(2)(2+) are less reliable, since the equatorial Cl ligands perturb the excited-state energies considerably. Calculated changes of the Np-O bond lengths are in agreement with the observed short symmetric-stretching progressions in the f-f spectra and longer progressions in the CT spectra of neptunyl. A possible luminescence spectrum of the lowest quartet CT state is predicted.     

Cation-cation interactions: crystal structures of neptunyl(V) selenate hydrates, (NpO2)2(SeO4)(H2O)n (n=1, 2, and 4)

Green crystals of (NpO(2))(2)(SeO(4))(H(2)O)(4), (NpO(2))(2)(SeO(4))(H(2)O)(2), and (NpO(2))(2)(SeO(4))(H(2)O) have been prepared by hydrothermal methods. The structures of these compounds have been characterized by single-crystal X-ray diffraction. (NpO(2))(2)(SeO(4))(H(2)O)(4), isostructural with (NpO(2))(2)(SO(4))(H(2)O)(4), is constructed from layers comprised of corner-sharing neptunyl(V) pentagonal bipyramids and selenate tetrahedra that are further linked by hydrogen bonding with water molecules. Each NpO(2)(+) cation binds to four other NpO(2)(+) units through cation-cation interactions (CCIs) to form a distorted "cationic square net" decorated by SeO(4)(2-) tetrahedra above and below the layer. Each selenate anion is bound to two neptunyl(V) cations through monodentate linkages. (NpO(2))(2)(SeO(4))(H(2)O)(2) is isostructural with the corresponding sulfate analogue as well. It consists of puckered layers of neptunyl(V) pentagonal bipyramids that are further connected by selenate tetrahedra to form a three-dimensional framework. The CCI pattern in the neptunyl layers of dihydrate is very similar to that of tetrahydrate; however, each SeO(4)(2-) tetrahedron is bound to four NpO(2)(+) cations in a mondentate manner. (NpO(2))(2)(SeO(4))(H(2)O) crystallizes in the monoclinic space group P2(1)/c, which differs from the (NpO(2))(2)(SO(4))(H(2)O) orthorhombic structure due to the slightly different connectivities between NpO(2)(+) cations and anionic ligands. The structure of (NpO(2))(2)(SeO(4))(H(2)O) adopts a three-dimensional network of distort neptunyl(V) pentagonal bipyramids decorated by selenate tetrahedra. Each NpO(2)(+) cation connects to four other NpO(2)(+) units through CCIs and also shares an equatorial coordinating oxygen atom with one of the other units in addition to the CC bond to form a dimer. Each SeO(4)(2-) tetrahedron is bound to five NpO(2)(+) cations in a monodentate manner. Magnetic measurements obtained from the powdered tetrahydrate are consistent with a ferromagnetic ordering of the neptunyl(V) spins at 8(1) K, with an average low temperature saturation moment of 1.98(8) μ(B) per Np. Well above the ordering temperature, the susceptibility follows Curie-Weiss behavior, with an average effective moment of 3.4(2) μ(B) per Np and a Weiss constant of 14(4) K. Correlations between lattice dimensionality and magnetic behavior are discussed.     

Synthesis, characterization, electrochemistry, electronic structure, and isomerization of mononuclear oxo-molybdenum(V) complexes: the serine gate hypothesis in the function of DMSO reductases

Crystal structures of DMSO reductases isolated from two different sources and the crystal structure of related trimethylamine-N-oxide reductase indicate that the angle between the terminal oxo atom on the molybdenum and the serinato oxygen varies significantly. To understand the significance of this angular variation, we have synthesized two isomeric compounds of the heteroscorpionato ligand (L1OH) (cis- and trans-(L1O)Mo(V)OCl(2)), where the phenolic oxygen mimics the serinato oxygen donor. Density functional and semiempirical calculations indicate that the trans isomer is more stable than the cis. The lower stability of the cis isomer can be attributed to two factors. First, a strong antibonding interaction between the phenolic oxygen with molybdenum d(xy) orbital raises the energy of this orbital. Second, the strong trans influence of the terminal oxo group in the trans isomer places the phenol ring, and hence the bulky tertiary butyl group, in a less sterically hindered position. In solution, the cis isomer spontaneously converts to the thermodynamically favorable trans isomer. This geometric transformation follows a first-order process, with an enthalpy of activation of 20 kcal/mol and an entropy of activation of -9 cal/mol K. Computational analysis at the semiempirical level supports a twist mechanism as the most favorable pathway for the geometric transformation. The twist mechanism is further supported by detailed mass spectral data collected in the presence of excess tetraalkylammonium salts. Both the cis and trans isomers exhibit well-defined one-electron couples due to the reduction of molybdenum(V) to molybdenum(IV), with the cis isomer being more difficult to reduce. Both isomers also exhibit oxidative couples because of the oxidation of molybdenum(V) to molybdenum(VI), with the cis isomer being easier to oxidize. This electrochemical behavior is consistent with a higher-energy redox orbital in the cis isomer, which has been observed computationally. Collectively, this investigation demonstrates that by changing the O(t)-Mo-O(p) angle, the reduction potential can be modulated. This geometrically controlled modulation may play a gating role in the electron-transfer process during the regeneration steps in the catalytic cycle.     

Two new neptunyl(V) selenites: a novel cation-cation interaction framework in (NpO2)3(OH)(SeO3)(H2O)2 3H2O and a uranophane-type sheet in Na(NpO2)(SeO3)(H2O)

Dark green crystals of (NpO(2))(3)(OH)(SeO(3))(H(2)O)(2)·H(2)O (1) have been prepared by a hydrothermal reaction of neptunyl(V) and Na(2)SeO(4) in an aqueous solution at 150 °C, while green plates of Na(NpO(2))(SeO(3))(H(2)O) (2) have been synthesized by evaporation of a solution of neptunyl(V), H(2)SeO(4), and NaOH at room temperature. Both compounds have been characterized by single-crystal X-ray diffraction. The structure of compound contains three crystallographically unique Np atoms that are bonded to two O atoms to form a nearly linear O═Np═O NpO(2)(+) cation. Neighboring Np(5+) ions connect to each other through a bridging oxo ion from the neptunyl unit, a configuration known as cation-cation interactions (CCIs), to build a complex three-dimensional network. More specifically, each Np(1)O(2)(+), Np(2)O(2)(+), and Np(3)O(2)(+) cation is involved in three, five, and four CCIs with other units, respectively. The framework of neptunyl(V) pentagonal bipyramids is decorated by selenite trigonal pyramids with one-dimensional open channels where uncoordinated waters are trapped via hydrogen bonding interactions. Compound adopts uranophane-type [(NpO(2))(SeO(3))](-) layers, which are separated by Na(+) cations and water molecules. Within each layer, neptunyl(V) pentagonal bipyramids share equatorial edges with each other to form a single chain that is further connected by both monodentate and bidentate selenite trigonal pyramids. Crystallographic data: compound, monoclinic, P2(1)/c, Z = 4, a = 6.6363(8) ?, b = 15.440(2) ?, c = 11.583(1) ?, β = 103.549(1)°, V = 1153.8(2) ?(3), R(F) = 0.0387 for I > 2σ(I); compound (2), monoclinic, C2/m, Z = 4, a = 14.874(4) ?, b = 7.271(2) ?, c = 6.758(2) ?, β = 112.005(4)°, V = 677.7(3) ?(3), R(F) = 0.0477 for I > 2σ(I).     

Electronic transitions and vibronic coupling in neptunyl compounds

The low-lying electronic transitions of the neptunyl (NpO(2)(2+)) ion are characterized as either charge transfer (CT) or intra- 5f. Comparison of these classes of electronic transitions reveals significantly different photophysical properties, especially in vibronic coupling. An empirical model developed for analyses of uranyl CT vibronic transitions is used here to simulate the absorption (excitation) spectra of neptunyl in two compounds of different chemical compositions and structural symmetries. Analyses reveal that CT vibronic coupling in neptunyl has the same characteristics as that in typical uranyl analogues. The primary profile of the CT spectra is similar for neptunyl respectively with respect to chloride- and oxide-neptunium bonding interactions. On the other hand, vibronic coupling to the CT transitions is significantly different from that of f-f transitions, even within a given neptunyl compound. Electronic energy levels, vibronic coupling strength, and frequencies of various vibration modes were evaluated for transitions to the excited states of different origins in the region from 8000 cm(-1) to 21000 cm(-1) for two neptunyl compounds.     

Isomerization and oxygen atom transfer reactivity in oxo-Mo complexes of relevance to molybdoenzymes

Both dioxo Mo(VI) and mono-oxo Mo(V) complexes of a sterically restrictive N2O heteroscorpionate ligand are found to exist as cis and trans isomers. The thermodynamically stable isomer differs for the two oxidation states, but in each case, we have isolated the kinetically labile isomer and followed its isomerization to the thermodynamically stable form. The Mo(VI) complex is more stable in the cis geometry and isomerizes more than 6 times faster than the Mo(V) complex, which prefers the trans geometry. In OAT reactions with PPh3, the trans isomer of the dioxo-Mo(VI) reacts approximately 20 times faster than the cis isomer. Thus, there are both oxidation state and donor atom dependent differences in isomeric stability and reactivity that could have significant functional implications for molybdoenzymes such as DMSO reductase.     

Oxidation-state and metal-ion dependent stereoisomerization in oxo molybdenum and tungsten complexes of a bulky alkoxy heteroscorpionate ligand

Monooxo Mo(V) complexes of a N2O heteroscorpionate ligand designated (L10O) are found to exist as isolable cis and trans isomers. We have been able to trap the kinetically labile cis isomer and follow its isomerization to the thermodynamically more stable trans form. We have also followed the kinetics of isomerization between the cis and trans isomers of the corresponding dioxo Mo(VI) and W(VI) species. Here the trans is the labile isomer that spontaneously converts to the thermodynamically more stable cis. It is observed that at 60 degrees C in DMSO the Mo(VI) complex isomerizes approximately 6.5 times faster than the Mo(V) and nearly 5 times faster than the corresponding W(VI) analogs. The temperature dependence to the kinetics of the Mo(V) and Mo(VI) isomerizations give activation parameters that are similar for both oxidation states and consistent with those previously observed in [(L1O)MoOCl2] suggesting a similar twist mechanism is operating in all cases. Thus there are oxidation state, metal ion and donor atom dependent differences in isomeric stability that could have significant implications for understanding the mechanisms of both enzymatic and nonenzymatic oxo atom transfer reactions catalyzed by complexes of Mo, W and Re.     

Spectrophotometric Determination of Vanadium in Complex Materials Using N-m-TMBHA and Thiocyanate

Abstract

Vanadium(V) reacts with N-m-Tolyl-p-methoxy benzohydroxamic acid to form 1:2 (metal to ligand) complex containing a basic V=O group and an acidic V-OH group, which forms addition compounds with thiocyanate to give a hyper and bathochromic effect in chloroform. On the basis of this bathochromic effect of thiocyanate a rapid, selective and sensitive method for the spectrophotometric determination of vanadium(V) has been developed. The blue coloured complex of vanadium(V) is extractable in chloroform having absorption maxima at 580nm and max 7100 ±50 1. mole^?1 cm^?1. The method is free from interferences of Mo(VI), W(VI), Zr(IV) and has been successfully applied for the analysis of steels and other complex materials.     

Structural and models of dioxouranium(VI) with rhodanine azodyes--V.

The synthesis of several new coordination compounds of dioxouranium(VI) heterochelates with bidentate rhodanineazol compounds derived from rhodanine are described. The ligands and uranyl complexes have been charcaterized by various physico-chemical techniques. The bond lengths and the force constants have been calculated from asymmetric stretching frequency of O-U-O group. The infrared spectral studies showed a monobasic bidentate behaviour with the oxygen and azonitrogen donor system. The ligands contain intramolecular hydrogen bonds.     

Specific incorporation of chalcogenide bridge atoms in molybdenum/tungsten-iron-sulfur single cubane clusters

An extensive series of heterometal-iron-sulfur single cubane-type clusters with core oxidation levels [MFe(3)S(3)Q](3+,2+) (M = Mo, W; Q = S, Se) has been prepared by means of a new method of cluster self-assembly. The procedure utilizes the assembly system [((t)Bu(3)tach)M(VI)S(3)]/FeCl(2)/Na(2)Q/NaSR in acetonitrile/THF and affords product clusters in 30-50% yield. The trisulfido precursor acts as a template, binding Fe(II) under reducing conditions and supplying the MS(3) unit of the product. The system leads to specific incorporation of a μ(3)-chalcogenide from an external source (Na(2)Q) and affords the products [((t)Bu(3)tach)MFe(3)S(3)QL(3)](0/1-) (L = Cl(-), RS(-)), among which are the first MFe(3)S(3)Se clusters prepared. Some 16 clusters have been prepared, 13 of which have been characterized by X-ray structure determinations including the incomplete cubane [((t)Bu(3)tach)MoFe(2)S(3)Cl(2)(μ(2)-SPh)], a possible trapped intermediate in the assembly process. Comparisons of structural and electronic features of clusters differing only in atom Q at one cubane vertex are provided. In comparative pairs of complexes differing only in Q, placement of one selenide atom in the core increases core volumes by about 2% over the Q = S case, sets the order Q = Se > S in Fe-Q bond lengths and Q = S > Se in Fe-Q-Fe bond angles, causes small positive shifts in redox potentials, and has an essentially nil effect on (57)Fe isomer shifts. Iron mean oxidation states and charge distributions are assigned to most clusters from isomer shifts. ((t)Bu(3)tach = 1,3,5-tert-butyl-1,3,5-triazacyclohexane).