Synthesis and structure of cluster compounds containing a novel cluster core {Re4STe3}

Three novel cluster compounds K₄[Re₄STe₃(CN)₁₂]·₄H₂O (I), [{Cu(en)₂}₂Re₄STe₃(CN)₁₂]·₅H₂O (II) and [{Cu(trien)}₂Re₄STe₃(CN)₁₂]·2H₂O (III) (en is ethylenediamine, trien is triethylenetetraamine) containing a new cluster core {Re₄STe₃} have been prepared and structurally characterized. According to single crystal X-ray diffraction data, compound I is ionic and represents the arrangement of ions K⁺ and [Re₄STe₃(CN)₁₂]^4?; compounds II and III are molecular and formed by two cationic moieties {Cu(en)₂}²⁺ and {Cu(trien)}²⁺, respectively, coordinated to one cluster anion. In the solid state, S atom positions in the tetrahedron Q₄ (Q = S, Te) are disordered for all three compounds: in I and III sulfur atoms are split over all four Q positions, while in II over two positions.     

Self-assembly of a tetranuclear Ni4 cluster with an S = 4 ground state: the first 3d metal cluster bearing a mu4-eta2:eta2-O,O carbonate ligand

Reaction of nickel(II) acetate with H(3)L (2-(5-bromo-2-hydroxyphenyl)-1,3-bis[4-(5-bromo-2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) yields [Ni(2)L(OAc)(H(2)O)(2)].3MeCN.2H(2)O (1.3MeCN.2H(2)O), crystallographically characterized. 1 is unstable in solution for a long time and hydrolyzes to give [Ni(2)L(o-OC(6)H(3)BrCHO)(H(2)O)].2.25MeCN.H(2)O (2.2.25MeCN.H(2)O). In addition, 1 uptakes CO(2) from air in a basic methanol/acetonitrile solution, yielding [[Ni(2)L(MeOH)](2)(CO(3))].1.5MeOH.MeCN.H(2)O (3.1.5MeOH.MeCN.H(2)O). The X-ray characterization of 3 reveals that it is a tetranuclear nickel cluster, which can be considered as the result of a self-assembly process from two dinuclear [Ni(2)L](+) blocks, joined by a mu(4)-eta(2):eta(2)-O,O carbonate ligand. The coordination mode of the carbonate anion is highly unusual and, to the best of our knowledge, it has not been described thus far for first-row transition metal complexes or magnetically studied until now. Magnetic characterization of 1 and 3 shows net intramolecular ferromagnetic coupling between the metal atoms in both cases, with S = 2 and S = 4 ground states for 1 and 3, respectively.     

Synthesis and molecular and electronic structure of an unusual paramagnetic borohydride complex Mo(NAr)2(PMe3)2(eta2-BH4)

Reaction of Mo(NAr)2Cl2(DME) (Ar=2,6-C6H3iPr2, DME=1,2-dimethoxyethane) with NaBH4 and PMe3 in THF formed the paramagnetic Mo(V) d1 borohydride complex Mo(NAr)2(PMe3)2(eta2-BH4) (1). Compound 1, which was characterized by EPR spectroscopy and X-ray diffraction analysis, provides a rare example both of a paramagnetic bis(imido) group 6 compound and a structurally characterized molybdenum borohydride complex. Density functional theory calculations were used to determine the electronic structure and bonding parameters of 1 and showed that it is best viewed as a 19 valence electron compound (having a primarily metal-based SOMO) in which the BH4- ligand behaves as a sigma-only, 2-electron donor.     

Synthesis and molecular and electronic structures of a series of Mo3CoSe4 cluster complexes with three different metal electron populations

The synthesis, crystal structure, and magnetic properties of [Mo 3(CoCO)Se 4(dmpe) 3Cl 3] ( 1), [Mo 3(CoCl)Se 4(dmpe) 3Cl 3] ( 2), and [Mo 3(CoCl)Se 4(dmpe) 3Cl 3](TCNQ) ([ 2](TCNQ)) (dmpe = 1,2-bis(dimethylphosphanyl)ethane; TCNQ = 7,7,8,8-tetracyanoquinomethane) cubane-type complexes with 16, 15, and 14 metal electrons, respectively, are reported. These compounds complete the series of cobalt-containing Mo 3CoQ 4 (Q = S, Se) cubane-type complexes, which allows a complete analysis of the consequences of replacing the inner chalcogen and the metal electron count on the structural, magnetic, and electrochemical properties. The experimental evidence is theoretically supported and rationalized on the basis of density-functional theory calculations. For the 15-metal electron [Mo 3(CoCl)Se 4(dmpe) 3Cl 3] complex with S = (1)/ 2, both electron paramagnetic resonance and theoretical studies give support to a spin density mainly located on the heteroatom. The nature of the highest occupied molecular orbital upon chalcogen exchange within the Mo 3CoQ 4 (Q = S, Se) series remains essentially unchanged, whereas the nature of the ligand attached to Co (Cl or CO) results in a different ordering of the molecular orbital scheme. This behavior is explained by the absence of backdonation between an occupied d orbital of Co to an empty pi* Cl orbital, to yield frontier orbitals that differ from those of previous models.     

Synthesis, structure and reactivity of cuboidal-type cluster aqua complexes with W3PdS4 4+ core

The reaction of PdCl(2) with [W3S4(H2O)9]4+ in the presence of hypophosphorous acid in 2 M HCl gives cuboidal cluster [W3(PdCl)S4(H2O)9]3+ (1) which undergoes condensation and crystallises from Hpts solutions as edge-linked double cubane cluster [{W3PdS4(H2O)9}2](pts)(8).19H2O (pts = p-toluenesulfonate) (1'). The substitution of Cl- in (1) by different ligands was explored. The Pd atom in the cluster shows an exceptionally high reactivity in the isomerisation of the hydrophosphoryl H2P(O)(OH), HP(O)(OH)2, HPPh(O)(OH) and HPPh2(O) molecules into the corresponding hydroxo tautomers HP(OH)2, P(OH)3, PhP(OH)2 and Ph2P(OH) stabilised by coordination at Pd. The reactions were followed by UV-Vis spectrophotometry and 31P NMR. Formation constants of the 1 : 1 coordination of [M3(PdCl)S4(H2O)9]3+ (M = Mo, W) with HP(OH)2 and As(OH)3 were obtained. The structures of cucurbit[6]uril (C36H36N24O12, CUC[6]) adducts [W3(PdP(OH)3)S4(H2O)8Cl]-(C36H36N24O12)Cl3.12.5H2O (2), and [W3Pd(PhP(OH)2)S4(H2O)7Cl2]2(C36H36N24O12)Cl4.9H2O (3) were determined by single-crystal X-ray diffraction.     

Heterometallic cuboidal complexes as derivatives of the [MO3S4(H2O)9]4+ cluster

Heterometallic atoms can be incorporated into the Mo ₃ ^IV trinuclear ion [Mo₃S₄(H₂O)₉]⁴⁺ to give cuboidal complexes of the kind Mo₃MS₄, or related edge-linked species {Mo₃MS₄}₂, or corner-shared Mo₃S₄MS₄Mo₃ double cubes, depending on the heteroatom used. All of the products formed can be obtained as aqua ions. With four recent additions there are now 15 different heterometal atoms participating in this chemistry from Cr in Group 6 to Bi in Group 15. Preparative procedures, X-ray crystal structures, and distinctive properties including UV-Vis spectra, elution characteristics using Dowexcation exchange chromatography, ICP metal analyses, and the stoichiometries of reactions in which the heterometallic product is oxidized back to [Mo₃S₄(H₂O)₉]⁴⁺ (with release of the heterometal in an ionic form) are considered.Dedicated to Professor Jiaxi Lu on the occasion of his 80th birthday.     

Reaction of the Mo3S4 cluster with dimethylacetylenedicarboxylate: an ESR-active cluster and an organometallic cluster formed by alpha,beta-conjugate addition

A seven-electron cluster [Mo3(mu3-S){mu3-SC(CO(2)CH(3))=C(CO(2)CH(3))S}{mu-SC(CO(2)CH(3))=CH(CO(2)CH(3))}(dtp)3(mu-OAc)] [2, S2P(OC(2)H(5))2-; dtp = diethyldithiophosphate] and an organometallic cluster [Mo3(mu3-S){mu3-SC(CO(2)CH(3))=C(CO(2)CH(3))S}{mu-SC(CO(2)CH(3))CH(OCH(3))(CO2)}(dtp)2(CH(3)OH)(mu-OAc)](Mo-C) (3) were obtained by reaction in methanol of the sulfur-bridged trinuclear complex [Mo3(mu3-S)(mu-S)3(dtp)3(CH(3)CN)(mu-OAc)] (1) with dimethylacetylenedicarboxylate (DMAD). The X-ray structures of 2 and 3 revealed the adduct formation of two DMAD molecules to the respective Mo(3)S(4) cores. 2 is paramagnetic and obeys the Curie-Weiss law: the mu(eff) value at 300 K is 1.90 muB. The electron spin resonance signal was observed at 173 K. The density functional theory calculation of 2 demonstrated that the main components of the singly occupied molecular orbitals of alpha and beta spins are Mo d electrons and the main components of lowest unoccupied molecular orbitals are of Mo and the olefin moiety with one C-S bond. A one-electron reversible oxidation process of 2 was observed at E1/2 = -0.11 V vs Fc/Fc+. The electronic spectrum of 2 has a peak at 468 nm (epsilon = 2170 M(-1) cm(-1)) and shoulders at 640 (918) and 797 (605) nm, and 3 has shoulders at 441 (1740) and 578 (625) nm and a distinct peak at 840 (467) nm. An intermediate [Mo3(mu3-S){mu3-SC(CO(2)CH(3))=C(CO(2)CH(3))S}{mu-SC(CO(2)CH(3))=CH(CO(2)CH(3))}(dtp)3(mu-OAc)]+ (4) is tentatively suggested: a one-electron reduction of 4 gives 2, and a nucleophilic conjugate addition of CH(3)O- to the alpha,beta-unsaturated carbonyl group of 4 gives 3.     

A novel nonanuclear CuII carboxylate-bridged cluster aggregate with an S= 7/2 ground spin state

The Cu(II) aggregate in [Cu(9)(cpida)(6)(MeOH)(6)].6(MeOH)[H(3)cpida = 2-(carboxyphenyl)iminodiacetic acid] is made up of two weakly ferromagnetically coupled carboxylate-bridged Cu(4) units that are antiferromagnetically linked through a central Cu(II) to give a Cu(9) core with an S= 7/2 spin ground state.     

Photoelectron spectrum and ground state electronic structure of chromyl chloride vapor

The electronic structure of chromyl chloride CrO₂Cl₂ has been investigated by ultraviolet (HeI) photoelectron spectroscopy. Mulliken-Wolfsberg-Helmholtz molecular orbital calculations have been performed in order to provide a model for interpretation of the photoelectron spectra and to assist in assigning the low-energy optical absorption and emission transitions. The first ionization potential of CrO₂Cl₂ at 11.8 eV is due to ionization of the near-degenerate oxygen and chlorine nonbonding 2a₂, 4b₁, and 4b₂ MO's. The first unoccupied orbital is basically a chromium dπ^* orbital. The excitations (2a₂, 4b₁, 4b₂)→ 7a₁^* correlate well with the three low energy absorption transitions observed.     

Electronic structure of the Fe3S4 cluster and its quasi-aromaticity

The localized molecular orbitals and their energy levels for the clusters [Fe₃S₄(SH)₃]^2–, [(HS)₃Fe₃S₄·Ni(PH₃)]^2–, [Mo₃S₄(OH₂)₉]⁴⁺, and [Mo₃S₄·Ni]⁴⁺ have been calculated by mean of the Edmiston-Ruedenberg energy localization technique under the CNDO/2 approximation in order to reveal the resemblance between [Fe₃S₄]⁺ and [Mo₃S₄]⁴⁺ in the geometrical configurations and the addition reactivities with heterometal atoms. It is shown that in these two cluster species with core {M ₃(₃-S)(-S)₃} of similar structure (M = Mo, Fe) there exist three synergically connected three-centered two-electron (M-S-M) -bonds around the puckered six-membered {M₃S₃} rings on account of delocalization of a lone electron pair on each bridging S atom; these (M-S-M) -bonds are thus capable of forming cubane-like heterometal clusters with intruder metal atoms through the ( M) bonding. It is therefore seen that unlike the [Mo₃S₄]⁴⁺ with appreciable bonding between the Mo atoms, the extra d-electrons on the metal atoms in the [Fe₃S₄]⁺ cluster are localized on the Fe atoms, exhibiting an electronic structure significantly different from that of the [Mo₃S₄]⁴⁺ cluster.     

X-ray emission and X-ray photoelectron studies of the electronic structure of the polymeric cubane cluster compounds Mo4S4Cl4, GaMo4S8, and GaMo4S4Te4

X-ray emission and X-ray photoelectron spectroscopy was used to study the electronic structures of the polymeric cubane cluster compounds Mo₄S₄Cl₄, GaMo₄S₈, and GaMo₄S₄Te₄. It is revealed that the ligand orbitals make significant contributions to the highest occupied molecular orbitals (M−M bonds). Substitution in the series Cl−S−Te increases the covalence of the metal—bridging ligand bonds. The experimental spectra allowed the construction of a qualitative scheme of the electronic structure of Mo₄S₄Cl₄. Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 6, pp. 1038–1045, November–December, 1995. Translated by I. Izvekova     

An evolved explanation for the molecular geometry and electronic structure of diphenyl-substituted cyclic trimethylenemethane in the ground state: a nearly planar conformation with a considerably localized electronic state

[structures: see text] We reinvestigated the molecular geometry and electronic structure of the diphenyl-substituted, five-membered cyclic trimethylenemethane (TMM) diradical (Berson's TMM, 3**) using UV/VIS absorption and emission spectroscopy combined with density functional theory (DFT) and time-dependent (TD)-DFT calculations. Two intense absorption bands, A and B, with lambda(ab) at 298 and 328 nm, respectively, a weak absorption band C, with lambda(ab) at 472 nm, and an intense emission band D, with lambda(em) at 491 nm, were observed for 3**. By comparing the spectrum of 3** with those of the 1,1-diphenylethyl (7*) and cyclopent-2-en-1-yl (9*) radicals, it was found that bands B, C, and D originated from the diphenylmethyl radical moiety (subunit I), while band A should most likely be assigned to an electronic transition related to an interaction between subunit I and residual subunit II, the cyclopentenyl radical moiety. An UB3LYP/cc-pVDZ calculation indicated that, in the ground state, the two unpaired electrons of 3** are mainly localized in subunits I and II, respectively, and the interaction between them is inefficient, despite the nearly planar conformation (theta = +23.5 degrees). Furthermore, a TD-UB3LYP/cc-pVDZ calculation suggested that absorption band A is assigned to an electronic transition involved with enhancement of the electron density of the C-2-C-3 bond. Substituent effects on the absorption and emission spectra of 3** using 11** and 13** support the conclusion based on the experiments and calculations. Therefore, we propose an evolved explanation for the molecular geometry and electronic structure of the ground state of 3** in a low-temperature matrix, a nearly planar conformation with a considerably localized electronic state, which alone accounts for the spectroscopic characteristics.     

Molecular structure,conformational stability,energetic and intramolecular hydrogen bonding in ground,and electronic excited state of 3-mercapto propeneselenal

In the present work, a conformational analysis of 3-mercapto propeneselenal is performed using several computational methods, including DFT (B3LYP), MP2, and G2MP2. At the DFT and G2MP2 levels the most stable conformers of title compound are characterized by an extended backbone structure, minimizing the steric repulsions between the sulfur and selenium lone pairs. Two conformers exhibit hydrogen bonding. This feature, although not being the dominant factor in energetic terms, appears to be of foremost importance to define the geometry of the molecule. The influence of the solvent on the stability order of conformers and the strength of intramolecular hydrogen bonding was considered using the PCM, SCI–PCM, and IEF–PCM methods. The results of analysis by quantum theory of “Atoms in Molecules” and natural bond orbital method fairly support the DFT results. The calculated HOMO and LUMO energies showed that charge transfer occurs within the molecule. Further verification of the obtained transition state structures was implemented via intrinsic reaction coordinate analysis. Calculations of the ¹H NMR chemical shift at GIAO/B3LYP/6–311++G** levels of theory are also presented. The excited-state properties of intramolecular hydrogen bonding in hydrogen-bonded systems have been investigated theoretically using the time-dependent density functional theory method.     

Synthesis, structure, and bonding of BaTl(3): an unusual competition between cluster and classical bonding in the thallium layers.

The new BaTl(3) compound has been synthesized and characterized by physical property measurements and electronic structure calculations. Its structure (Cmcm) is a new intermediate in the Ni(3)Sn family (P6(3)/mmc), and consists of thallium layers formed from two-center bond formation between the parallel chains of face-sharing octahedral clusters. The valence electron concentration (VEC) of the thallium layers is consistent with their two-dimensional nature, in comparison with those in other AX(3)-type compounds with one- or three-dimensional anionic networks with the same building blocks and different VECs. The unique geometric features of the anionic thallium layers bring on an unusual competition between inter- and intracluster bonds. Detailed studies of the energetics of BaTl(3) reveal for the first time the important role of cation-anion interactions in the bonding competition in such an anionic substructure.     

Slow magnetic relaxation of a ferromagnetic Ni(II)5 cluster with an S = 5 ground state

Complex [Ni 5{pyCOpyC(O)(OMe)py} 2(O 2CMe) 4(N 3) 4(MeOH) 2].2MeOH.2.6H 2O ( 1.2MeOH.2.6H 2O) was synthesized by the reaction of Ni(O 2CMe) 2.4H 2O with pyCOpyCOpy and NaN 3 in refluxing MeOH. It crystallizes in the monoclinic C2/ c space group and consists of five Ni (II) atoms in a helical arrangement. Direct current magnetic susceptibility studies reveal ferromagnetic interactions between the Ni (II) ( S = 1) ions, stabilizing an S = 5 ground state. Alternating current susceptibility experiments revealed the existence of out-of-phase signals indicative of slow magnetic relaxation. Analysis of the signals showed that they are composite, suggesting more than one relaxation process, while analysis of their magnitudes suggests not all molecules undergo slow magnetic relaxation. Magnetization field-sweep experiments revealed hysteresis at 1.8 K, and magnetization decay experiments clearly verified the appearance of slow magnetic relaxation at that temperature.     

Synthesis and molecular structure of 6-aryl-3-ethoxycarbonyl-4-hydroxypyridazines

EthylZ-5-aryl-2-diazo-5-hydroxy-3-oxopent-4-enoates interact with triphenylphosphine to give 6-aryl-3-ethoxycarbonyl-4-hydroxypyridazines (Ar=Ph, 4-MeC₆H₄, 4-ClC₆H₄). Quantum-chemical calculations (MNDO) were performed to estimate the tautomeric equilibrium in the latter using a 6-phenyl-substituted derivative as an example. Acetylation of the 4-hydroxypyridazines led to 4-acetoxy-6-aryl-3-ethoxycarbonylpyridazines. The structure of the latter was confirmed by an X-ray diffraction analysis of 4-acetoxy-3-ethoxycarbonyl-6-(p-tolyl)pyridazine. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2260–2263, December, 1997.     

Probing the intrinsic electronic structure of the cubane [4Fe-4S] cluster: nature's favorite cluster for electron transfer and storage

The cubane [4Fe-4S] is the most common multinuclear metal center in nature for electron transfer and storage. Using electrospray, we produced a series of gaseous doubly charged cubane-type complexes, [Fe4S4L4]2- (L = -SC2H5, -SH, -Cl, -Br, -I) and the Se-analogues [Fe4Se4L4]2- (L = -SC2H5, -Cl), and probed their electronic structures with photoelectron spectroscopy and density functional calculations. The photoelectron spectral features are similar among all the seven species investigated, revealing a weak threshold feature due to the minority spins on the Fe centers and confirming the low-spin two-layer model for the [4Fe-4S](2+) core and its "inverted level scheme". The measured adiabatic detachment energies, which are sensitive to the terminal ligand substitution, provide the intrinsic oxidation potentials of the [Fe4S4L4]2- complexes. The calculations revealed a simple correlation between the electron donor property of the terminal thiolate as well as the bridging sulfide with the variation of the intrinsic redox potentials. Our data provide intrinsic electronic structure information of the [4Fe-4S] cluster and the molecular basis for understanding the protein and solvent effects on the redox properties of the [4Fe-4S] active sites.