Investigation of single MoFe3S4 cubane cluster: I. First successful synthesis by spontaneous self-assembly reaction and structure of (Et4N) [MoFe3S4(Et2NCSS)5]CH3CN

A single MoFe₃S₄ cubane-like cluster compound has been synthesized through spontaneous self-assembly of simple inorganic salts with organosulfur ligand for the first time. (Et₄N)-(MoFe₃S₄(Et₂NCSS)₅] CH₃CN(1) is quite stable in air. The crystal of 1 is monoclinic with space group P2/c, a=22.897 (3)Å, b= 12.399 (2)Å, c=20.928 (4)Å, β=97.15 (1)°, and Z=4. A full matrix least-squares refinement with 6725 unique reflections for all nonhydrogen atoms gives R=0.068. The anion of 1 is the first isolated single MoFe₃S₄ cubane cluster with core oxidation state [MoFe₃S₄]⁴⁺. The distance between the two 6-coordinate metal atoms (Mo, Fe) is 2.624 Å, which is the shortest M-M' bond observed for Mo-Fe-S clusters so far and the only one shorter than similar distances in FeMo-cofactor. The bond orders of this anion were calculated by EHMO method and the results coincide with the general rule. The structural feature and the unusual stability of 1 can be attributed to the bidentate chelating effect of Et₂NCSS-, which leads to high coordination of metal atoms and the various ligated types.     

Precursors to clusters with the topology of the P(N) cluster of nitrogenase: edge-bridged double cubane clusters [(Tp)2Mo2Fe6S8L4]z: synthesis, structures, and electron transfer series

Members of the cluster set [(Tp)2Mo2Fe6S8L4]z contain the core unit M2Fe6(mu3-S)6(mu4-S)2 in which two MoFe3S4 cubanes are coupled by two Fe-(mu4-S) interactions to form a centrosymmetric edge-bridged double cubane cluster. Some of these clusters are synthetic precursors to [(Tp)2Mo2Fe6S9L2]3-, which possess the same core topology as the P(N) cluster of nitrogenase. In this work, the existence of a three-member electron-transfer series of single cubanes [(Tp)MoFe3S4L3](z) (z = 3-, 2-, 1-) and a four-member series of double cubanes [(Tp)2Mo2Fe6S8L4]z (z = 4-, 3-, 2-, 1-) with L = F-, Cl-, N3, PhS- is demonstrated by electrochemical methods, cluster synthesis, and X-ray structure determinations. The potential of the [4-/3-] couple is extremely low (<-1.5 V vs SCE in acetonitrile) such that the 4- state cannot be maintained in solution under normal anaerobic conditions. The chloride double cubane redox series was examined in detail. The members [(Tp)2Mo2Fe6S8Cl4]4-,3-,2- were isolated and structurally characterized. The redox series includes the reversible steps [4-/3-] and [3-/2-]. Under oxidizing conditions, [(Tp)2Mo2Fe6S8Cl4]2- cleaves with the formation of single cubane [(Tp)MoFe3S4Cl3]1-. The quasireversible [2-/1-] couple is observed at more positive potentials than those of the single cubane redox step. Structure comparison of nine double cubanes suggests that significant dimensional changes pursuant to redox reactions are mainly confined to the Fe2(mu4-S)2 bridge rhomb. The synthesis and structure of [(Tp)2Mo2Fe6S9F2.H2O]3-, a new topological analogue of the P(N) cluster of nitrogenase, is described. (Tp = hydrotris(pyrazolyl)borate(1-)).     

Controlled Incorporation of Nitrides into W‐Fe‐S Clusters

Incorporation of monatomic 2p ligands into the core of iron–sulfur clusters has been researched since the discovery of interstitial carbide in the FeMo cofactor of Mo‐dependent nitrogenase, but has proven to be a synthetic challenge. Herein, two distinct synthetic pathways are rationalized to install nitride ligands into targeted positions of W‐Fe‐S clusters, generating unprecedented nitride‐ligated iron–sulfur clusters, namely [(Tp*)₂W₂Fe₆(μ₄‐N)₂S₆L₄]^2? (Tp*=tris(3,5‐dimethyl‐1‐pyrazolyl)hydroborate(1?), L=Cl^? or Br^?). ⁵⁷Fe Mössbauer study discloses metal oxidation states of W^IV₂Fe^II₄Fe^III₂ with localized electron distribution, which is analogous to the mid‐valent iron centres of FeMo cofactor at resting state. Good agreement of Mössbauer data with the empirical linear relationship for Fe–S clusters indicates similar ligand behaviour of nitride and sulfide in such clusters, providing useful reference for reduced nitrogen in a nitrogenase‐like environment.     

Synthesis,Structures and Magnetic Properties of Cyano‐bridged FeIII/MnIII Heterobimetallic 1D Chain Complexes

Using the tricyanometalate building block, (nBu₄N)[(Tp*)Fe(CN)₃] [Bu₄N⁺ = tetrabutylammonium cation; Tp*^– = hydrotris(3,5‐dimethylpyrazol‐1‐yl)borate], and bidentate Schiff base ligands, HL1 or HL2 {HL1 = 2‐[[(2‐phenylethyl)imino]methyl]phenol; HL2 = 4‐methoxy‐2‐[[(2‐phenylethyl)imino]methyl]phenol}, two heterobimetallic one‐dimensional (1D) chain complexes, [Mn(L1)₂Fe(Tp*)(CN)₃]_n ( 1 ) and [Mn(L2)₂Fe(Tp*)(CN)₃]_n ( 2 ), were synthesized. Single crystal X‐ray diffraction reveal the formation of neutral cyano‐bridged zigzag single chains in 1 and 2 . Magnetic studies demonstrate that both complexes show ferromagnetic interactions between central Fe^III and Mn^III atoms.     

Synthesis and Structure of Tetrameric Germa‐closo‐dodecaborate Silver Halides

The reaction of germa‐closo‐dodecaborate with oneequivalent of silver halide AgX (X = Cl, Br) leads to the tetrameric1:1 adducts [Et₃MeN]₈[{AgCl(GeB₁₁H₁₁)}₄] ( 1 ) and [Et₃MeN]₈[{AgBr(GeB₁₁H₁₁)}₄] ( 2 ). A cubane‐like structure was determined in the solid state by single‐crystal X‐ray diffraction. The compounds were characterized by crystal structure analysis, ¹¹B NMR spectroscopy and elemental analysis.     

Kohlenwasserstoffverbrückte Metallkomplexe. L Dicarbonyl‐cyclopentadienyl‐pyridoyl‐eisen‐Komplexe als Liganden

Hydrocarbon‐bridged Metal Complexes. L Dicarbonyl Cyclopentadienyl Pyridoyl Iron Complexes as Ligands Dicarbonyl‐cyclopentadienyl‐2‐ and 3‐pyridoyl‐iron (L¹, L²) and 2,6‐dicarbonyl‐pyridine‐bis(dicarbonyl‐cyclopentadienyl‐iron) (L³) function as ligands in metal complexes and the N,O‐chelates [(OC)₄M(L¹)] (M = Mo, W, 8 a, b ) and [(Ph₃P)₂Cu(L¹)]⁺BF₄^– ( 9 ) were prepared. Monodentate coordination of L¹ and L² through the pyridine N‐atom occurs in the palladium(II) complexes [Cl₂Pd(PnBu₃)(L¹)] ( 10 ), [Cl₂Pd(PnBu₃)(L²)] ( 11 ) and [Cl₂Pd(L²)₂] ( 12 ). Ligand L³ forms the O,N,O‐bis(chelate) [Cl₂Zn(L³)] ( 13 ). The crystal and molecular structures of L¹, 8 b (M = W), 9–11 and 13 were determined by X‐ray diffraction.     

Borohydride, azide, and chloride anions as terminal ligands on Fe/Mo/S clusters. Synthesis, structure and characterization of [(Cl4-cat)(PPr3) MoFe3S4(X)2]2(Bu4N)4 and [(Cl4-cat)(PPr3)MoFe3S4 (PPr3)(X)]2(Bu4N)2 (X = N3-, BH4-, Cl-) double-fused cubanes. NMR reactivity studies of [(Cl4-cat)(PPr3) MoFe3S4(BH4)2]2(Bu4N)4

Our explorations of the reactivity of Fe/Mo/S clusters of some relevance to the FeMoco nitrogenase have led to new double-fused cubane clusters with the Mo2Fe6S8 core as derivatives of the known (Cl4-cat)2Mo2Fe6S8(PPr3)6 (I) fused double cubane. The new clusters have been obtained by substitution reactions of the PPr3 ligands with Cl-, BH4-, and N3-. By careful control of the conditions of these reactions, the clusters [(Cl4-cat)(PPr3)MoFe3S4(BH4)2]2(Bu4N)4 (II), [(Cl4-cat)(PPr3)MoFe3S4(PPr3)(BH4)]2(Bu4N)2 (III), [(Cl4-cat)(PPr3)MoFe3S4(N3)2]2(Bu4N)4 (IV), [(Cl4-cat)(PPr3)MoFe3S4(PPr3)(N3)]2(Bu4N)2 (V), and [(Cl4-cat)(PPr3)MoFe3S4Cl2]2(Et4N)4 (VI) have been obtained and structurally characterized. A study of their electrochemistry shows that the reduction potentials for the derivatives of I are shifted to more positive values than those of I, suggesting a stabilization of the reduced clusters by the anionic ligands BH4- and N3-. Using 1H NMR spectroscopy, we have explored the lability of the BH4- ligand in II in coordinating solvents and its hydridic character, which is apparent in its reactivity toward proton sources such as MeOH or PhOH.     

Haloperoxidase‐like Compounds: Synthesis,Structure and Properties of Two New Oxidovanadium‐Poly(pyrazolyl)borate‐Carboxylate Complexes

Two new oxidovanadium (IV) complexes: TpVO(L₁) ( 1 ) and Tp*VO(pzH*)(L₂) ( 2 ) [Tp = hydrotris(pyrazolyl)borate, HL₁ = 5‐methyl‐1H‐pyrazole‐3‐carboxylic acid, Tp* = hydrotris(3,5‐dimethylpyrazolyl)borate, pzH* = 3,5‐dimethylpyrazole, HL₂ = 5‐phenyl‐1H‐pyrazole‐3‐carboxylic acid] have been synthesized and characterized by elemental analysis and IR spectroscopy. The single‐crystal structures of the complexes shows that the vanadium ion is in a distorted octahedral environment with a N₄O₂ donor set in each complex. Additionally, hydrogen bonding interaction exits in both complexes. Interestingly, the molecules of 1 are held together to form a 1D hydrogen bonded polymer along the b axis, whereas complex 2 is a hydrogen bonded dimer. In addition, the catalytic activities of complexes 1 and 2 in bromination reactions in phosphate buffer with phenol red as a trap were evaluated primary by UV/Vis spectroscopy. Furthermore, ab initio calculations of complexes 1 and 2 were performed.     

Bis(acetonitrile‐κN)bis[hydridotris(3,5‐dimethylpyrazol‐1‐yl‐κN2)borato]di‐μ3‐sulfido‐tetra‐μ2‐sulfido‐di‐μ2‐thiocyanato‐κ2N:S;κ2S:N‐tetracopper(I)ditungsten(VI)

Reactions of (Et₄N)[Tp*WS₃] [Tp* is hydridotris(3,5‐dimethylpyrazol‐1‐yl)borate] with CuSCN in MeCN in the presence of melamine afforded the title neutral dimeric cluster [Cu₄W₂(C₁₅H₂₂BN₆)₂(NCS)₂S₆(C₂H₃N)₂] or [Tp*W(μ₂‐S)₂(μ₃‐S)Cu(μ₂‐SCN)(CuMeCN)]₂, which has two butterfly‐shaped [Tp*WS₃Cu₂] cores bridged across a centre of inversion by two (CuSCN)⁻ anions. The S atoms of the bridging thiocyanate ligands interact with the H atoms of the methyl groups of the Tp* units of a neighbouring dimer to form a C—H...S hydrogen‐bonded chain. The N atoms of the thiocyanate anions interact with the H atoms of the methyl groups of the Tp* units of neighbouring chains, affording a two‐dimensional hydrogen‐bonded network.     

Structure and Reactivity of an Asymmetric Synthetic Mimic of Nitrogenase Cofactor

The Mo nitrogenase catalyzes the ambient reduction of N₂ to NH₃ at its M‐cluster site. A complex metallocofactor with a core composition of [MoFe₇S₉C], the M‐cluster, can be extracted from the protein scaffold and used to facilitate the catalytic reduction of CN^?, CO, and CO₂ into hydrocarbons in the isolated state. Herein, we report the synthesis, structure, and reactivity of an asymmetric M‐cluster analogue with a core composition of [MoFe₅S₉]. This analogue, referred to as the Mo‐cluster, is the first synthetic example of an M‐cluster mimic with Fe and Mo positioned at opposite ends of the cluster. Moreover, the ability of the Mo‐cluster to reduce C₁ substrates to hydrocarbons suggests the feasibility of developing nitrogenase‐based biomimetic approaches to recycle C₁ waste into fuel products.     

Racemic and chiral 1‐[N‐(chloro­acetyl)carbamoylamino]‐2,3‐dihydro‐1H‐inden‐2‐yl chloroacetate

In the racemic crystals of (1S,2R)‐ or (1R,2S)‐1‐[N‐(chloro­acetyl)­carbamoyl­amino]‐2,3‐di­hydro‐1H‐inden‐2‐yl chloro­acetate, C₁₄H₁₄Cl₂N₂O₄, (I), the enantiomeric mol­ecules form a dimeric structure via the N—H?O cyclic hydrogen bond of the carbamoyl moieties. In the chiral crystals of (—)‐(1S,2R)‐1‐[N‐(chloro­acetyl)­carbamoyl­amino]‐2,3‐di­hydro‐1H‐inden‐2‐yl chloro­acetate, C₁₄H₁₄Cl₂N₂O₄, (II), the N—­H?O intermolecular hydrogen bond forms a zigzag chain around the twofold screw axis. The melting points and calculated densities of (I) and (II) are 446 and 396 K, and 1.481 and 1.445 Mg m^?3, respectively.     

Controllable ring‐opening copolymerization of L‐lactide and (3S)‐benzyloxymethyl‐(6S)‐methyl‐morpholine‐2,5‐dione initiated by a biogenic compound creatinine acetate

Ring‐opening copolymerization (ROCP) of L ‐lactide (L ‐LA) and (3S)‐benzyloxymethyl‐(6S)‐methyl‐morpholine‐2,5‐dione [(3S, 6S)‐BMMD] initiated by creatinine acetate, a biogenic organic compound, was performed in the bulk at 130 °C. The copolymerization was well controlled as evidenced by that both the measured values of number‐average molecular weight (M_n,NMR(OH) and M_n,NMR(COOH)) and serine molar fraction (F_Bz.ser) of synthesized copolymers were close to the corresponding theoretical values; and that the higher isotacticity of synthesized copolymers (85–86%) and lower racemization degree of the ROCP. After removing O‐benzyls of the copolymers with Et₃SiH/Et₃N/CH₂Cl₂ under catalysis of PdCl₂, functional biodegradable copolymers of L ‐lactic acid (L ‐Lac) and L ‐Ser with designed molar fraction of serine (F_ser 1.35%, 3.57%, 5.41%), narrow molecular weight distribution (polydispersity index 1.10–1.36), and improved hydrophilicity (θ_stat 82.3–89.6°) were finally obtained. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis of a molecular Mo2Fe6S9 cluster with the topology of the PN cluster of nitrogenase by rearrangement of an edge-bridged Mo2Fe6S8 double cubane

The structures of the P cluster and cofactor cluster of nitrogenase are well-defined crystallographically. They have been obtained only by biosynthesis; their chemical synthesis remains a challenge. Synthetic routes are sought to the P cluster in the P(N) state in which two cuboidal Fe(3)S(3) units are connected by a mu(6)-S atom and two Fe-(mu(2)-S(Cys))-Fe bridges. A reaction scheme affording a Mo(2)Fe(6)S(9) cluster in molecular form having the topology of the P(N) cluster has been devised. Reaction of the single cubane [(Tp)MoFe(3)S(4)Cl(3)](1)(-) with PEt(3) gives [(Tp)MoFe(3)S(4)(PEt(3))(3)](1+) (2), which upon reduction with BH(4)(-) affords the edge-bridged all-ferrous double cubane [(Tp)(2)Mo(2)Fe(6)S(8)(PEt(3))(4)] (4) (Tp = tris(pyrazolylhydroborate(1-)). Treatment of 4 with 3 equiv of HS(-) produces [(Tp)(2)Mo(2)Fe(6)S(9)(SH)(2)](3)(-) (7) as the Et(4)N(+) salt in 86% yield. The structure of 7 is built of two (Tp)MoFe(3)(mu(3)-S)(3) cuboidal fragments bridged by two mu(2)-S atoms and one mu(6)-S atom in an arrangement of idealized C(2) symmetry. The cluster undergoes three one-electron oxidation reactions and is oxidatively cleaved by p-tolylthiol to [(Tp)MoFe(3)S(4)(S-p-tol)(3)](2)(-) and by weak acids to [(Tp)MoFe(3)S(4)(SH)(3)](2-). The cluster core of 7 has the bridging pattern [Mo(2)Fe(6)(mu(2)-S)(2)(mu(3)-S)(6)(mu(6)-S)](1+) with the probable charge distribution [Mo(3+)(2)Fe(2+)(5)Fe(3+)S(9)](1+). Cluster 7 is a topological analogue of the P(N) cluster but differs in having two heteroatoms and two Fe-(mu(2)-S)-Fe instead of two Fe-(mu(2)-S(Cys))-Fe bridges. A best-fit superposition of the two cluster cores affords a weighted rms deviation in atom positions of 0.38 A. Cluster 7 is the first molecular topological analogue of the P(N) cluster. This structure had been prepared previously only as a fragment of complex high-nuclearity Mo-Fe-S clusters.     

A Three-dimensional Heteronuclear Polymer of [Ag2Fe（SCN）5（DMF）]n Containing Channels and One-dimensional Ag2S2-S-Ag2S2 Chains with Ag…Ag Interaction

Introduction So far, considerable attention has been paid to mag-netic interaction between two different metal ions.1-3 As a potential bridging ligand, thiocyanate can coordinate to a harder metal center with N atom and softer ones with S atom at the same time, resulting in the formation of small ferromagnetic coupling.2 On the other hand, the Fe(III) atom is a good candidate as a hard acid and Ag(I) is a good candidate as a soft acid, so that the Fe(III) centers could be expected to conn…     

Reactions of Stable α‐Chlorosulfanyl Chlorides with CS‐Functionalized Compounds

The smooth reaction of 3‐chloro‐3‐(chlorosulfanyl)‐2,2,4,4‐tetramethylcyclobutanone ( 3 ) with 3,4,5‐trisubstituted 2,3‐dihydro‐1H‐imidazole‐2‐thiones 8 and 2‐thiouracil ( 10 ) in CH₂Cl₂/Et₃N at room temperature yielded the corresponding disulfanes 9 and 11 (Scheme 2), respectively, via a nucleophilic substitution of Cl^? of the sulfanyl chloride by the S‐atom of the heterocyclic thione. The analogous reaction of 3‐cyclohexyl‐2,3‐dihydro‐4,5‐diphenyl‐1H‐imidazole‐2‐thione ( 8b ) and 10 with the chlorodisulfanyl derivative 16 led to the corresponding trisulfanes 17 and 18 (Scheme 4), respectively. On the other hand, the reaction of 3 and 4,4‐dimethyl‐2‐phenyl‐1,3‐thiazole‐5(4H)‐thione ( 12 ) in CH₂Cl₂ gave only 4,4‐dimethyl‐2‐phenyl‐1,3‐thiazol‐5(4H)‐one ( 13 ) and the trithioorthoester derivative 14 , a bis‐disulfane, in low yield (Scheme 3). At ?78°, only bis(1‐chloro‐2,2,4,4‐tetramethyl‐3‐oxocyclobutyl)polysulfanes 15 were formed. Even at ?78°, a 1 : 2 mixture of 12 and 16 in CH₂Cl₂ reacted to give 13 and the symmetrical pentasulfane 19 in good yield (Scheme 5). The structures of 11, 14, 17 , and 18 have been established by X‐ray crystallography.     

Synthesen und Kristallstrukturen neuer heterobimetallischer Tantal‐Münzmetall‐Chalkogenido‐Cluster

Syntheses and Crystal Structures of Novel Heterobimetallic Tantalum Coin Metal Chalcogenido Clusters In the presence of phosphine the thiotantalats (Et₄N)₄[Ta₆S₁₇] · 3MeCN reacts with copper to give a number of new heterobimetallic tantalum copper chalcogenide clusters. These clusters show metal chalcogenide units some of which here already known from the chemistry of vanadium and niobium. New Ta—M‐chalcogenide clusters could also be synthesised by reaction of TaCl₅ and silylated chalcogen reagents with copper or silver salts in presence of phosphine. Such examples are: [Ta₂Cu₂S₄Cl₂(PMe₃)₆] · DMF ( 1 ), (Et₄N)[Ta₃Cu₅S₈Cl₅(PMe₃)₆] · 2MeCN ( 2 ), (Et₄N)[Ta₉Cu₁₀S₂₄Cl₈(PMe₃)₁₄] · 2MeCN ( 3 ), [Ta₄Cu₁₂Cl₈S₁₂(PMe₃)₁₂] ( 4 ), (Et₄N)[Ta₂Cu₆S₆Cl₅(PPh₃)₆] · 5MeCN ( 5 ), (Et₄N)[Ta₂Cu₆S₆Cl₅(PPh₂Me)₆] · 2MeCN ( 6 ), (Et₄N)[Ta₂Cu₆S₆Cl₅(P^tBu₂Cl)₆] · MeCN ( 7 ) [Ta₂Cu₂S₄Br₄(PPh₃)₂(MeCN)₂] · MeCN ( 8 ), [Cu(PMe₃)₄]₂[Ta₂Cu₆S₆(SCN)₆(PMe₃)₆] · 4MeCN ( 9 ), [TaCu₅S₄Cl₂(dppm)₄] · DMF ( 10 ), [Ta₂Cu₂Se₄(SCN)₂(PMe₃)₆] ( 11 ), [Cu(PMe₃)₄]₂[Ta₂Cu₆Se₆(SCN)₆(PMe₃)₆] · 4MeCN ( 12 ), [TaCu₄Se₄(PⁿPr₃)₆][TaCl₆] ( 13 ), [Ta₂Ag₂Se₄Cl₂(PMe₃)₆] · MeCN ( 14 ), _∞[TaAg₃Se₄(PMe₃)₃] ( 15 ). The structures of these compounds were obtained by X‐ray single crystal structure analysis.     

Novel and Stereospecific Synthesis of (2S)‐3‐(2,4,5‐Trifluorophenyl)propane‐1,2‐diol from D‐Mannitol

A stereospecific synthesis of (2S)‐3‐(2,4,5‐trifluorophenyl)propane‐1,2‐diol from D ‐mannitol has been developed. The reaction of 2,3‐O‐isopropylidene‐D ‐glyceraldehyde with 2,4,5‐trifluorophenylmagnesium bromide gave [(4R)‐2,2‐dimethyl‐1,3‐dioxolan‐4‐yl](2,4,5‐trifluorophenyl)methanol in 65% yield as a mixture of diastereoisomers (1 : 1). The Ph₃P catalyzed reaction of the latter with C₂Cl₆ followed by reduction with Pd/C‐catalyzed hydrogenation gave (2S)‐3‐(2,4,5‐trifluorophenyl)propane‐1,2‐diol with >99% ee and 65% yield.     

[MoFe3S4]3+ and [MoFe3S4]2+ cubane clusters containing a pentamethylcyclopentadienyl molybdenum moiety

A series of organometallic molybdenum/iron/sulfur clusters of the general formula [Cp¹MoFe₃S₄L_n]^m (Cp¹ = η⁵-C₅Me₅; L = S^tBu, SPh, Cl, I, n = 3, m = 1−; L_n = I₂(P^tBu₃), m = 0; L = 2,6-diisopropylphenylisocyanide (ArNC), n = 7, m = 1+) have been synthesized. A cubane cluster (PPh₄)[Cp¹MoFe₃S₄(S^tBu)₃] (2) was isolated from a self-assembly reaction of Cp¹Mo(S^tBu)₃ (1), FeCl₃, LiS^tBu, and S₈ followed by cation exchange with PPh₄Br in CH₃CN, while an analogous cluster (PPh₄)[Cp¹MoFe₃S₄(SPh)₃] (3) was obtained from the Cp¹MoCl₄/FeCl₃/LiSPh/PPh₄Br reaction system or from a ligand substitution reaction of 2 with PhSH. Treatment of 2 with benzoyl chloride gave rise to (PPh₄)[Cp¹MoFe₃S₄Cl₃] (4), which was in turn converted to (PPh₄)[Cp¹MoFe₃S₄I₃] (5) by the reaction with NaI. A neutral cubane cluster Cp¹MoFe₃S₄I₂(P^tBu₃) (6) was generated upon treating 5 with P^tBu₃. Although reduction of 4 by cobaltocene under the presence of ArNC resulted in a disproportionation of the cubane core to give Fe₄S₄(ArNC)₉Cl (7), a similar reduction reaction of 5 produced [Cp¹MoFe₃S₄(ArNC)₇]I (8), where the MoFe₃S₄ core was retained. The crystal structures of 4–6, and 8 were determined by the X-ray analysis.     

Synthesis,Structure and Magnetic Properties of a Cyano‐bridged Dinuclear Compound fac‐{[FeIII(pzTp)(CN)2(μ‐CN)] CuII(TPyA)}·Et2O·ClO4 (pzTp = tetrakis(pyrazolyl)borate)

The reaction of tricyanometallate precursor, (Bu₄N)[(pzTp)Fe(CN)₃] with Cu(ClO₄)₂·6H₂O in the presence of the tetradentate ligand tris(2‐pyridylmethyl)amine (TPyA) afford the dinuclear compound fac‐{[Fe^III(pzTp)(CN)₂(μ‐CN)]Cu^II(TPA)}·Et₂O·ClO₄ ( 1 ) (pzTp = tetrakis(pyrazolyl)borate). The molecular structure was determined by single‐crystal X‐ray diffraction. In compound 1 , the Fe^III ion is coordinated by three cyanide carbon atoms and three nitrogen atoms of pzTp anions. Whereas, the Cu^II ion is surrounded by one cyanide nitrogen atom and four nitrogen atoms from the TPyA ligand. Magnetic measurements indicate the intramolecular ferromagnetic coupling is observed for compound 1 , and it has S = 1 ground states.     

Synergism in molybdenum iron sulphur cluster compounds. Synthetic,structural, magnetic,cyclic voltammetric evidence and the reaction of dicubane clusters containing [MoFe3S4] unit

Summary Dicubane cluster compounds (Et₄N)₄[Mo₂Fe₇S₈(SR)₁₂] (2A) (R=Ph,a;o-tolyl,b;m-tolyl,c;p-tolyl,d) were made by reaction of (Et₄N)₂[Fe₄(SR)₁₀] (1) with (Et₄N)₂MoS₄ in MeCN at room temperature. The structure,¹Hn.m.r.,⁵⁷Fe Mössbauer spectrum, magnetic susceptibility and cyclic voltammogram are described. (Et₄N)₃[Mo₂Fe₆S₈Cl₆(SR)₃] (3) (R=Ph,a;m-tolyl,b) was obtained from the reaction of (2Aa) or (2Ac) with acetyl chloride in MeCN. This is the first time that compound of structural type (2) is transformed into that of structural type (3) by chemical conversion. Compound (2Aa) crystallizes in the triclinic space group P with Z=1 and unit cell dimensionsa=12.775(4),b=13.076(3), andc=20.576(4) Å; the structure was refined to R=7.7% using 4031 unique data with I>3(I_o). Compound (2Ac) 2THF crystallizes in the monoclinic space group P2₁/n with Z=2 and unit cell dimensionsa=18.022(2),b=18.375(2) andc=22.254(3) Å; the structure was refined to R=6.4% using 5173 unique data with I>3(I_o). Compound (3b) crystallizes in the hexagonal space groupP6₃/m with Z=2 and unit cell dimensionsa=b=16.827(3) andc=15.951(16) Å; the structure was refined to R=4.9% using 1296 unique data with I>3(I_o). Its characteristics are discussed and compared with those of known compounds. The ratios of core volumes S₄/M₄ are within the 2.34–2.40 range for core oxidation level [MoFe₃S₄]³⁺ indicating that distortion of the cubane core is a general phenomenon. Different thiolato ligands induce significant changes of structural parameters only at the Fe(SR)₆ region for compound (2A) while terminal chlorides induce changes over the whole molecule of (3b) with the latter structure more comparable to [Mo₂Fe₆S₈(SPh)₉]^5– (3f) with [MoFe₃S₄]²⁺ core than to [Mo₂Fe₆S₈(SPh)₉]^3– (3d). The isotropic shifts of (2A) originate mainly from -contact interaction. Both¹H n.m.r. spectra and magnetic susceptibility measurements indicate practically no magnetic interaction among the three magnetic centres,i.e. a Fe(SR)₆ bridge and two [MoFe₃S₄(SR)₃] units. CV studies showed that the reduction of cubane unit having aromatic thiolates is easier than that having aliphatic thiolates as the aliphatic group is electron-donating. In addition, the very similar differences of E_p,c for first and second cubane units in compounds (2A) and in (3d) and (3e) imply that the effect of the first reduced unit [MoFe₃S₄]²⁺ upon the second unit [MoFe₃S₄]³⁺ is very similar in the two types of dicubane cluster compounds. Synergism in Mo–Fe–S cluster compounds is thus proposed to play an important role in their structural correlation with reactivities and must function in nitrogenase.