Nitrosyl complexes of cobalt with hybrid bidentate ligands containing phosphorus and sulfur donor atoms

Nitric oxide reacts with [Co(PSR)₂](BF₄)₂ (PSR  1-(thioalkyl)-2-(diphenylphosphino)ethane) to form five-coordinate mononitrosyl {CoNO}⁸ complexes. On the basis of infrared and NMR data the [Co(NO)(PSR)₂]²⁺ cations are believed to have a trigonal–bipyramidal geometry, with a linear Co–NO linkage. The mononitrosyl derivatives disproportionate in solution giving [Co(NO)₂(PSR)₂]⁺ species, and probably Co(III) compounds. The stoichiometry of this reaction was examined in different solvents and in the presence of added halide or pseudohalide ions by NMR and IR techniques. The cobalt(III) complex [Co(NCS)₂(PSEt)₂]BF₄ has been isolated and characterized.     

Structure and O2 uptake properties of a novel nickel(II) complex of pyridyl-pendant dioxocyclam [1-(2-pyridyl)methyl-5,7-dioxo-1,4,8,11-tetraazacyclotetradecane]

 Novel potentially five-coordinate pyridyl–pendant dioxocyclam [1-(2-pyridyl)methyl-5,7-dioxo-1,4,8,11-tetraazacyclotetradecane (H₂L) and its homologs (6-methyl and 6,6-dimethyl derivatives)] have been synthesized to study nickel(II) complexation. A purple nickel(II) complex with a deprotonated amide (NiHL) was isolated from aqueous equimolar solution of H₂L and Ni(ClO₄)₂. A yellow nickel(II) complex with two deprotonated amides (NiL) was crystallized from an H₂O/CH₃CN solution of H₂L and Ni(OH)₂. The X-ray crystal study of NiL showed a square-planar nickel(II) complex with the pyridyl–pendant remaining uncoordinated. It is concluded from the visible absorption and NMR study of NiL in aqueous solution that the four-coordinate NiL is in equilibrium with a five-coordinate square-pyramidal nickel(II) complex with the apical coordination of the pyridyl–pendant. A voltammetric study disclosed a low nickel(II/III) redox potential of +0.29 V vs SCE for NiL at pH 9.5 and 25  °C with 0.10 M Na₂SO₄. The nickel(II) complex NiL absorbed an equimolar amount of O₂ at pH 9.5 and 25  °C, and the O₂ was activated to cleave plasmid DNA. Received: 5 August 1996 / Accepted: 24 October 1996     

The crystal and molecular structures of dioxo mo(VI) complexes of tripodal,tetradentate N,S-donor ligands

The crystal and molecular structures of the complexes MoO₂((SCH₂CH₂)₂NCH₂CH₂SCH₃), I and MoO₂((SCH₂CH₂)₂NCH₂CH₂N(CH₃)₂), II, have been determined from X-ray intensity data collected by counter methods. Compound I crystallizes in two forms, Ia and Ib. In form Ia the space group is P2₁/n with cell parameters a = 7.235(2), b = 7.717(2), c = 24.527(6) Å, β = 119.86(2)°, V = 1188(1) ų, Z = 4. In form Ib the space group is P2₁/c with cell parameters a = 14.945(5), b = 11.925(5), c = 14.878(4) Å, β = 114.51(2)°, V = 2413(3) ų, Z = 8. The molecules of I in Ia and Ib are very similar having an octahedral structure with cis oxo groups, trans thiolates (cis to both oxo groups) and N and thioether sulfur atoms trans to oxo groups. Average ditances are MoO = 1.70, MoS (thiolate) = 2.40, MoN = 2.40 and MoS (thioether) = 2.79 Å. Molecule II crystallizes in space group P2₁2₁2₁ with a = 7.188(1), b = 22.708(8), c = 7.746(2) Å, V = 1246(1) ų and Z = 4. The coordination about Mo is octahedral with cis oxo groups, trans thiolates and N atoms trans to oxo. Distances in the first coordination sphere are MoO = 1.705(2), 1.699(2), MoS = 2.420(1), 2.409(1) and MoN = 2.372(2), 2.510(2) Å. The conformational features of the complexes are discussed. Complex I displays MoO and MoS distances which are very similar to those found by EXAFS in sulfite oxidase. This similarity is discussed.     

Cobalt hexafluoroacetylacetonate polyether adducts for thin films of cobalt oxides

The novel [Co(C₅F₆HO₂)₂ · 2H₂O · CH₃(OCH₂CH₂)₂OCH₃] and [Co(C₅F₆HO₂)₂ · 2H₂O · CH₃(OCH₂CH₂)₃OCH₃] low-melting adducts have been synthesized and characterized by elemental analysis, IR spectroscopy, mass spectra and TG-DTG thermal measurements. The former adduct is liquid at room temperature, whilst very mild heating of the latter results in a thermal stable liquid compound. Both adducts can easily be evaporated. Deposition experiments, in a low-pressure horizontal hot-wall reactor, on optical transparent SiO₂ substrates, using these precursors, result in CoO or Co₃O₄ films, depending on the deposition conditions. XRD measurements provide evidence that CoO and Co₃O₄ consist of cubic, highly oriented, (2 0 0) and (3 1 1) crystals, respectively. The mean crystallite sizes were evaluated from the XRD line broadening. Both optical spectra and resistivity measurements of Co₃O₄ films show that they are semi-conducting and their band-gap was determined from the optical induced transitions. The film cross section and the surface atomic composition were investigated by SEM and XPS analyses, respectively.     

Mechanism of toxicity of platinum(II) compounds in repair-deficient strains of Escherichia coli

The survival of wild-type and repair-deficient Escherichia coli treated with cis-Pt(NH₃)₂Cl₂, trans-Pt(NH₃)₂Cl₂ and [Pt(dien)Cl]Cl (dien = H₂NCH₂CH₂NHCH₂CH₂NH₂) was inversely correlated with the ability of these compounds to inhibit DNA synthesis in different bacterial strains. The relative amounts of these 3 compounds covalently bound to DNA immediately after treatment with the same dose were, respectively, 1:?2:1, their relative abilities to inhibit DNA synthesis were 6:1:0 and their relative toxicities toward the wild-type and uvrA strains were 3–5:1:0. More repair synthesis, as measured by density-gradient centrifugation techniques, was observed in wild-type bacteria after treatment with the cis than with the trans isomer whereas no repair synthesis was detected after exposure to [Pt(dien)Cl]Cl.These results are consistent with the hypothesis that cis-Pt(NH₃)Cl₂ binds to DNA and inhibits DNA synthesis thereby killing the cell. The lower toxicity of this compound toward wild-type bacteria compared with repair-deficient strains is in part a consequence of DNA repair. trans-Pt(NH₃)₂Cl₂ and [Pt(dien)Cl]Cl are less toxic than the cis isomer; this lesser toxicity is not a consequence of low levels of DNA binding or enhanced repair of the lesions but appears to reflect a weaker inhibition of DNA synthesis by these Pt-DNA adducts.     

Some ambiguities in using the esr spectra of high-spin CoII species as “Structure Markers”

Co(ethylenethiourea)₂(CH₃CO₂)₂, with a pseudo-tetrahedral structure but having a long-bonded fifth ligand, gives an esr spectrum almost identical with that of Co-Bovine Carbonic Anhydrase-OH; a previous assignment of a similar structure to the Co^II-containing enzyme is then substantiated. Several other tetrahedral and trigonal-bipyramidal Co^II complexes have also been investigated. Although none gives δ values close to those of CoBCAOH and the correlation high δ = trigonal bipyramidal, low δ = tetrahedral seems to hold, the influence of even minor distortions within pseudo-tetrahedral symmetry on the esr spectra indicates that, used alone, esr spectra may not be an unambiguous structure marker for Co^II enzymes.     

Solvent Effects in the Spin Trapping Of Lipid Oxyl Radicals

Studies documenting spin trapping of lipid radicals in defined model systems have shown some surprising solvent effects with the spin trap DMPO. In aqueous reactions comparing the reduction of H₂O₂ and methyl linoleate hydroperoxide (MLOOH) by Fe^z+, hydroxyl (HO·) and lipid alkoxyl (LO·) radicals produce identical four-line spectra with line intensities 1:2:2:1. Both types of radicals react with commonly-used HO· scavengers, e.g. with ethanol to produce ·C(CH₃)HOH and with dirnethylsulfoxide (DMSO)togive ·CH₃. However, DMSO radicals (either ·CH₃or ·OOCH₃) react further with lipids, and when radicals are trapped in these MLOOH systems, multiple adducts are evident. When acetonitrile is added to the aqueous reaction systems in increasing concentrations, ·CH₂CN radicals resulting from HO· attack on acetonitrile are evident, even with trace quantities of that solvent. In contrast, little, if any, reaction of LO· with acetonitrile occurs, even in 100% acetonitrile. A single four-line signal persists in the lipid systems as long as any water is present, although the relative intensity of the two center lines decreases as solvent-induced changes gradually dissociate the nitrogen and β-hydrogen splitting constants. Extraction of the aqueous-phase adducts into ethyl acetate shows clearly that the identical four-line spectra in the H₂0₂ and MLOOH systems arise from different radical species in this study, but the lack of stability of the adducts to phase transfer may limit the use of this technique for routine adduct identification in more complex systems. These results indicate that the four-line 1:2:2:1. a_N = a_H = 14.9G spectrum from DMPO cannot automatically be assigned to the HO· adduct in reaction systems where lipid is present, even when the expected spin adducts from ethanol or DMSO appear confirmatory for HO-. Conclusive distinction between HO· and LO· ultimately will require use of ¹³C-labelled DMPO or HPLC-MS separation and specific identification of adducts when DMPO is used as the spin trap.     

Synthesis of cobalt(III) complexes with novel open chain oxime ligands and metal-ligand coordination in aqueous solution

Cobalt(III) complexes with new open chain oxime ligands: N,N′-bis(2-hydroxyiminopropionyl)-1,2-aminoethane (H₂pen) and N,N′-bis(2-hydroxyiminopropionyl)-1,3-diaminopropane (H₂pap) have been investigated. Single crystals of Co(papH₋₁)(Im₂)·CH₃OH (1) and Co(papH₋₁)(MEA)₂·1.5H₂O (2) (where Im = imidazole, MEA = monoethanolamine) suitable for X-ray crystallography were grown by slow evaporation of methanol/water solutions at room temperature. The molecular structures have been determined using single-crystal X-ray diffraction methods. The potentiometric and spectrophotometric results in aqueous solution reveal that both of the open chain ligands show a very high efficacy in the coordination of Co(II) ions. As it has been indicated, differences between the two oxime ligands in complexing ability may be attributed to the longer -CH₂- chain in H₂pap and by that a better fit of the relatively large Co(II) ion to the accessible binding site. One of the complex species confirmed under inert atmosphere, namely of type Co(LH₋₁)⁻ (where L = pap or pen), has been shown as the “active” form, capable of dioxygen uptake followed by irreversible oxidation to Co(III).     

Crystal structure of [chloro(diethyldithiocarbamato)butyl phenyl]tin(IV)

The crystal structure of the title compound, SnCl(C₆H₅)(C₄H₉)[S₂CN(C₂H₅)₂], was determined and refined to an R factor of 3.2% for 4876 reflections. The molecule contains five-coordinate tin in a distorted trigonal bipyramidal arrangement with the tin atom lying 0.20 Å below the equatorial plane formed by one of the sulphur atoms, S(1), and the donor carbons of the butyl and phenyl groups. The chlorine and the other sulphur atom, S(2), occupy axial sites, making a S(2)SnCl angle of 156.85(1)°. The SnS(2) bond is markedly elongated (2.764(1) Å) compared to the SnCl bond (2.449(1) Å) and the SnS(1) bond (2.454(1) Å). The structure resembles those of analogues such as (C₆H₅)₂Sn(glygly) in having both hydrocarbon ligands located in the equatorial plane. Crystal data: space group P$\text{1}$: a = 8.291(2) Å, b = 14.726(3) Å, c = 9.509(2) Å, α = 96.24(2)°, β = 107.02(3)°, γ = 116.70(2)°, Z = 2, R = 3.2% for 4876 independent reflections.     

Synthesis and crystal and molecular structure of a methyl N,N-diethylcarbamylmethylenephosphonato dysprosium thiocyanate complex

Bis-Methyl N,N-diethylcarbamylmethylenephosphonato dysprosium thiocyanate, Dy[O₂P(OCH₃)CH₂C(O)N(C₂H₅)₂]₂(NCS) was prepared from the combination of ethanolic solutions of Dy(NCS)₃·xH₂O and (CH₃O)₂P(O)CH₂C(O)N(C₂H₅)₂. The complex was characterized by infrared and NMR spectroscopy, and single crystal X-ray diffraction methods. The crystal structure was determined at 25 °C from 3727 independent reflections by using a standard automated diffractometer. The complex was found to crystallize in the monoclinic space group P2₁/c with a = 13.282(4) Å, b = 19.168(5) Å, c = 9.648(2) Å, β = 90.09(2)°, Z = 4, V = 2456.4 ų and ?_cald = 1.72 g cm^?3. The structure was solved by standard heavy atom techniques, and blocked least-squares refinement converged with R_f = 4.7% and R_wF = 4.9%. The Dy atom is seven coordinate and bonded in a bidentate fashion to two anionic phosphonate ligands [O₂P(OCH₃)CH₂C(O)N(C₂H₅)₂^?] through the carbonyl oxygen atoms and one of two phosphonate oxygen atoms. In addition, each Dy atom is coordinated to two phosphonate oxygen atoms from two neighboring complexes and to the nitrogen atom of a thiocyanate ion. This coordination scheme gives rise to a two-dimensional polymeric structure. Some important bond distances include DyNCS 2.433(8) Å, DyO(carbonyl)_avg 2.39(2) Å, DyO(equat. phosphoryl)_avg 2.303(8) Å, DyO(axial phosphoryl)_avg 2.25(2), PO(phosphoryl)_avg 1.493(3) Å and CO(carbonyl)_avg 1.25(1) Å.     

The kinetics of ligand substitution in bis(N-alkylsalicylaldiminato)nickel(II) Complexes: a study on the reactivity of square-planar versus octahedral coordination

The bis(N-alkylsalicylaldiminato)nickel(II) complexes Ni(R-sal)₂ with R = CH(CH₂OH)CH(OH)Ph (I), R = CH(CH₃)CH(OH)Ph (II) and R = CH₂CH₂Ph (III; Ph = phenyl) were prepared and characterized. In the solid state I and II are paramagnetic (μ = 3.2 and 3.3 BM at 20 °C, respectively), whereas III is diamagnetic. It follows from the UV-Vis spectra that in acetone solution I is six-coordinate octahedral and III is four-coordinate planar, the spectrum of II showing characteristics of both modes of coordination. Vis spectrophotometry and stopped-flow spectrophotometry were applied to study the kinetics of ligand substitution in I–III by H₂salen (= N,N′-disalicylidene-ethylenediamine) in the solvent acetone at different temperatures. The kinetics follow a second-order rate law, rate = k[H₂-salen] [complex]. At 20 °C the sequence of rate constants is k(III):k(II):k(I) = 11 850:40.6:1. The activation parameters are ΔH^≠(I) = 112, ΔH^≠(II) = 40.7, ΔH^≠(III) = 35.7 kJ mol⁻¹ and ΔS^≠(I) = 92, ΔS^≠(II) = −103, ΔS^≠(III) = −89 J K⁻¹ mol⁻¹. The enormous difference in rate between complexes I, II and III, which is less pronounced in methanol, is attributed to the existence of a fast equilibrium planar ⇌ octahedral, which is established in the case of I and II by intramolecular octahedral coordination through the hydroxyl groups present in the organic group R. An A-mechanism is suggested to control the substitution in the sense that the entering ligand attacks the four-coordinate planar complex, the octahedral complex being kinetically inert.     

Reactions of methylcobalamin with tin and lead compounds

Reactions of CH₃[Co] with (CH₃)_nM^(4?n)+ (n = 2, 3; M = Sn, Pb) at concentrations high enough to detect (CH₃)₄M in the head space (yields 7.08×10^?5?2.06×10^?5%), indicate that dismutation is the major route of production. Similarly, kinetic reactions at lower concentrations show that no demethylation of CH₃[Co] by (CH₃)₃M⁺ (M = Sn, Pb) occurs after 60 days. From the methylation of SnCl₂ by CH₃[Co] at pD 1.0 and under aerobic conditions, the following hydrolysis species were observed in the 400 MHz ¹H NMR spectrum: CH₃- Sn(OH)Cl₂·2H₂O (63.6%), [CH₃Sn(OH)(H₂O)₄]²⁺ (17.6%) and CH₃Sn(OH)₂Cl·nH₂O (18.8%). No methylation products were observed from similar reactions with Pb(II) salts.     

Investigation on the coordination modes: Syntheses, characterization and crystal structures of diorganotin (IV) dichloride with 4(5)-imidazoledithiocarboxylic acid

A series of diorganotin (IV) complexes of the types of R₂SnCl(SSCC₃H₃N₂) (R = CH₃1, ⁿBu 2, C₆H₅3 and C₆H₅CH₂4), R₂Sn(SSCC₃H₃N₂)₂ (R = CH₃5, ⁿBu 6, C₆H₅7 and C₆H₅CH₂8) and R₂Sn(SSCC₃H₂N₂) (R = CH₃9, ⁿBu 10, C₆H₅11 and C₆H₅CH₂12) have been obtained by reactions of 4(5)-imidazoledithiocarboxylic acid with diorganotin (IV) dichlorides in the presence of sodium ethoxide. All complexes are characterized by elemental, IR, ¹H, ¹³C and ¹¹⁹Sn NMR spectra analyses. Also, the complexes 1, 7 and 9 are characterized by X-ray crystallography diffraction analyses, which reveal that the complex 1 is monomeric structure with five-coordinate tin (IV) atom, the complex 7 is monomeric structure with six-coordinate tin (IV) atom and the complex 9 is one-dimensional chain with five-coordinate tin (IV) atom.     

The direct electrochemical synthesis of zinc and cadmium derivatives of α,ω-alkanedithiols and their reaction with carbon disulphide

The anodic oxidation of zinc or cadmium in non-aqueous solutions of α,ω-alkanedithiols, HS(CH₂)_nSH (n=2−6) gives the corresponding M[S₂(CH₂)_n] species in high yield. When 2, 2′- bipyridine or 1, 10-phenanthroline are present in the cell, the products are the appropriate 1:1 adducts. These compounds react with carbon disulphide, but in general only one of the two MSC sites undergoes attack. The products are complexes involving one thiolato and one thioxanthato group in the ligand, and the thioxanthate is in the exocyclic

mode.     

The preparation and electrochemistry of cysteine-ester oxovanadium(IV) complexes

An improved synthesis of VO(CysOCH₃)₂, (CysOCH₃  the anion of cysteine methyl ester), is reported, as is an analogous preparation of VO(CysOCH₂CH₃)₂, (CysOCH₂CH₃  the anion of cysteine ethyl ester). These are the first two examples of isolated vanadium-cysteine compounds. The oxidation of VO(CysOCH₃)₂ in DMSO is a reversible one electron change at 0.24 V versus SCE followed by a rapid chemical reaction which produces a stable vanadium(V) species. This species is reduced back to the vanadium(IV) complex at −1.30 V. The electrochemistry of VO(Cys-OCH₂CH₃)₂ is nearly identical to that of the methyl ester compound.     

f-Element/crown ether complexes. 16. Synthesis,crystallization and crystal structure of [Dy(OH2)8]Cl3·18-crown-6·4H2O

When crystals of [Dy(OH₂)₇(OHMe)] [DyCl(OH₂)₂(18- crown-6)]₂Cl₇·2H₂O [1] are allowed to warm from 5 °C to ambient temperature (22 °C) under the original solvent mixture (1:3 CH₃OH: CH₃CN), they redissolve and the title complex can be isolated by slow evaporation of the resulting solution. The crystal structure of this complex, [Dy(OH₂)₈]Cl₃·18-crown-₆·4H₂O, has been determined. It crystallizes in the monoclinic space group, P2₁/c, with a = 10.395(1), b = 18.684(1), c = 16.259- (3) Å, β= 102.56(1)°, and D_calc = 1.61 g cm⁻³ for Z = 4. A final conventional R value of 0.041 was obtained by least-squares refinement using 3453 independent observed [F_o⩾5σ(F_o)] reflections. The [Dy(OH₂)₈]³⁺ cations and crown ether molecules are hydrogen bonded in a polymeric chain with the crown molecules separating the cations and a total of seven DyOH₂···O(crown ether) hydrogen bonds. The chains are connected by a hydrogen bonding network consisting of the cations, chloride ions, and uncoordinated water molecules. The geometry of the cation is best described as a bicapped trigonal prism with distortions on the reaction pathway toward dodecahedral symmetry. The two capping atoms average 2.41(1) Å from Dy, the remaining DyO distances average 2.38(2) Å. The 18-crown-6 molecule has the D_3d conformation normally observed except for a distortion of one OCCO unit containing the oxygen atom accepting two hydrogen bonds.     

Cobalt(II) and nickel(II) complexes with nitrogen-sulfur tripod ligands. Crystal and molecular structure of the five-coordinate complex bromotris(2-tert-butylthioethyl)aminecobalt(II) hexafluorophosphate (NS3Br donor set)

The tripod ligands tris(2-alkylthioethyl)amine, with alkyl = ethyl, iso-propyl, and tert-butyl, give with cobalt(II) and nickel(II) halides high-spin complexes with formulae [MLX₂], [MLX]Y, and [MLX]₂[MX₄] (where X = Cl, Br, I; Y = BPh₄, PF₆). The nickel complexes are either six- or five-coordinate: the coordination number decreases as the bulkiness of the alkyl group bound to the sulfur is increased. All the cobalt complexes contain the five-coordinate cation [CoLX]⁺. The crystal and molecular structure of the [Co(NS₃-t-Bu)Br]PF₆ complex has been determined by standard X-ray methods, and refined to R = 0.061. The crystals are monoclinic, space group P2¹/n. The unit cell dimensions are: a = 27.420 (2), b = 11.923 (4), c = 17.082 (1) Å, β = 102.40 (1)°, Z = 8. The complex cation has a trigonal bipyramidal geometry with the nitrogen and bromine atoms at the apexes, and the three sulfur atoms in the equatorial plane. The tetrahedral distortion is relatively small (mean BrCoS angle = 98.5°), and similar to that found for the [Co (Me₆tren)Br]Br complex [Me₆tren = tris(2-dimethylaminoethyl)amine).     

Transition-metal(II) thiocyanate coordination compounds containing 4-allyl-1,2,4-triazole. Structure and magnetic properties.

The synthesis and characterisation of a series of dinuclear and polynuclear coordination compounds with 4-allyl-1,2,4-triazole are described. Dinuclear compounds were obtained for Mn(II) and Fe(II) with composition [M₂(Altrz)₅(NCS)₄], and for Co(II) and Ni(II) with composition [M₂(Altrz)₄(H₂O)(NCS)₄](H₂O)₂. The crystal structure of [Co₂(Altrz)₄(H₂O)(NCS)₄](H₂O)₂ was solved at room temperature. It crystallizes in the monoclinic space group P2₁/n. The lattice constants are a = 18.033(3) Å, b = 13.611(2) Å, c = 15.619(3) Å, β = 92.04(2)° Z = 4. One cobalt ion has an octahedrally arranged donor set of ligands consisting of three vicinal nitrogens of 1,2-bridging triazoles (CoN = 2.14–2.15 Å), one terminal triazole nitrogen (CoN = 2.12 Å) and two N-bonded NCS anions (CON = 2.08 Å). The other Co(II) ion has the same geometry, but the terminal triazole ligand is replaced by H₂O (CoO = 2.15 Å). The crystal structure is stabilised by hydrogen bonding through H₂O molecules, S-atoms of the NCS anions and the lone-pair electron of the monodentate triazole. The magnetic exchange in the Mn, Co and Ni compounds is antiferromagnetic with J-values of ?0.4 cm^?1, ?10.9 cm^?1 and ?8.7 cm^?1 respectively. The Co compound was interpreted in terms of an Ising model. For [Zn₂(Altrz)₅(NCS)₂]∞[Zn(NCS)₄], [Cu₂(Altrz)₃(NCS)₄]∞ and [Cd₂(Altrz)₃(NCS)₄]∞ chain structures are proposed. In the Cu compound thiocyanates appear to be present, bridging via the nitrogen atom, as deduced from the IR spectrum.     

Structural comparison of octahedral MoO22+ complexes of bidentate and linear tetradentate N,S-donor ligands

The structures of MoO₂[NH₂C(CH₃)₂CH₂S]₂ and MoO₂[SC(CH₃)₂CH₂NHCH₂CH₂NHCH₂C(CH₃)₂S] have been determined using X-ray diffraction intensity data collected by counter techniques. MoO₂[NH₂C(CH₃)₂CH₂S]₂ crystallizes in space group Pbca with a = 11.234(3), b = 11.822(3) and c = 20.179(5) Å, V = 2680(2) ų and Z = 8. Its structure is derived from octahedral coordination with cis oxo groups [MoO = 1.705(3) and 1.705(3)], trans thiolate donors cis to the oxo groups [MoS = 2.416(1) and 2.402(1) and N donors trans to oxo [MoN = 2.325(3) and 2.385(4) Å]. MoO₂[SC(CH₃)₂CH₂NHCH₂CH₂NHCH₂C(CH₃)₂S] crystallizes in the space group P2₁/c with a = 10.798(5), b = 6.911(2), c = 20.333(9) Å, β = 95.20°, V = 1511(2) Å₃ and Z = 4. Its structure is very similar to that of MoO₂[NH₂C(CH₃)₂CH₂S]₂ with MoO = 1.714(2) and 1.710(2), MoS = 2.415(1) and 2.404(1) and MoN = 2.316(3) and 2.362(3). The small differences in the geometries of the two compounds are attributed to the constraints of the extra chelate ring in the complex with the tetradentate ligand. The structures in this paper stand in contrast to those reported for complexes of similar ligands wherein steric hindrance produces complexes with a skew trapezoidal bipyramidal structure.