Complexes of binucleating ligands. XVII. Some 3-atom N,C bridged palladium(II) complexes

The acetate-bridged complex, LPd₂(CH₃CO₂), in which L^3? is a binucleating ligand, reacts with 2-vinylpyridine in the presence of methanol or ethanol to generate the 3 atom N,C bridged complexes LPd₂(2-C₅H₄N·CH·CH₂OR) (R = Me or Et) whose ¹H and ¹³C nmr spectra indicate the presence in solution of two slowly interconverting forms at room temperature. The ¹H and ¹³C nmr spectra of two closely related pairs of 3 atom N,C bridged complexes of the form LPd₂(2-C₅H₄N·CH·X) and LPd₂ (HN = C(CH₃)·CH·X) (where X = COCH₃ or COOCH₃) show that the complexes with pyridine-containing bridges exist in solution at room temperature in two distinguishable forms whilst the corresponding imine-bridged complexes behave as single species. The existence of two forms of the complexes with pyridine-containing 3 atom N,C bridges, the natures of which are discussed in this paper, appears to be a consequence of steric interaction between the pyridine α hydrogen atom and the closely adjacent oxygen donor of L.     

Circular dichroism anisotrophy of DNA with different modifications at N7 of guanine.

The complexex DNA-Ag1+, DNA-Cu1+, protonated DNA and DNA methylated at N7 of guanine were oriented by pumping the solutions through a multicapillary cell in the direction of a light beam. The CD components along the DNA axis, delta epsilon parallel, and normal to it, 2 delta epsilon perpendicular, were calculated from the CD spectra of the oriented samples by the method of Chung and Holzwarth, (1975) J. Mol. Biol. 92, 449--466. It was shown that in most cases, except that of the protonated DNA, the degree of orientation was only slightly less than that for pure DNA. This demonstrated the absence of aggregation and of appreciable denaturation. In all cases the modifications of DNA give rise to a negative component 2 delta epsilon perpendicular, whose magnitude increased as the extent of modification increased. From both the CD spectra of non-oriented samples and the absorption spectra, an inference is drawn that Ag1+ and Cu1+ are attached to the same site as CH3 groups i.e., to the N7 atom of guanine. Proton transfer along the H-bond from the N1 atom of G to the N3 atom of the complementary cytosine is suggested to be a result of the modifications, although the case of H+-DNA may differ from the others. Based on the CD spectra for the anisotropic components, delta epsilon parallel and 2 delta epsilon perpendicular, it is proposed that ligand binding is accompanied by winding of the DNA helix.     

Substitution and racemization of 3-hydroxy- and 3-alkoxy-1,4-benzodiazepines in acidic aqueous solutions

Oxazepam (OX), 3-O-methyloxazepam, 3-O-ethyloxazepam, temazepam (TMZ), 3-O-methyltemazepam, and 3-O-ethyltemazepam underwent acid-catalyzed nucleophilic substitution reaction (hydrolysis) in an acetonitrile–oxygen-18 water mixture to form either OX or TMZ in which the 3-hydroxyl group was either partially or fully labeled with an oxygen-18 atom. The dependence of the hydrolysis rates on solvent composition, temperature, ionic strength, and in deuterated solvent was studied by reversed-phase high-performance liquid chromatography (HPLC). The rates of racemization of enantiomeric compounds in acidic aqueous solutions were studied by both spectropolarimetry and chiral stationary phase HPLC. In acetonitrile: 2.5 M H₂SO₄ (4:1, v/v) at 50°C, enantiomers of OX and TMZ underwent racemization at rates ≥40-fold faster than the rates of hydrolysis. Enantiomeric 3-O-alkyl derivatives of OX and TMZ in acidic aqueous solutions did not themselves undergo racemization and it was their hydrolysis products (either OX or TMZ) that underwent racemization. © 1995 Wiley-Liss, Inc.     

When identical functional groups are not identical: A DFT study of the effects of molecular environment on sulfur K-edge X-ray absorption spectra

Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations have been used to elucidate differences in the sulfur K-edge spectra of three pairs of related compounds: methionine and , cystine and (±)6-thioctic amide, and (Me)₂SO₃ and (CH₂)₂SO₃. TD-DFT is shown to accurately reproduce all the experimental XAS spectra. The 2 eV energy difference in the sulfur K-edge rising edge position between methionine and trimethylsulfonium is shown to derive from changes in bonding rather than the increase in effective nuclear charge. A similar insensitivity to effective nuclear charge is found in the XAS spectra of cystine and (±)6-thioctic amide. These surprising results are traced back to the fact that XAS spectra reflect orbital energy differences, rather than a measure of the atomic potential. The change in atomic potential following oxidation or reduction affects the core and valence orbitals almost equally. In all cases DFT calculations showed that the dramatic differences in sulfur K-edge spectra found between functional groups in alternative molecular environments derive from the variations in orbital mixing and energies following from bonding. However, XAS rising-edge energy positions have a near linear correlation with oxidation state. This is attributed to the fact that bond strength typically increases with oxidation state. Therefore, although XAS rising-edge energies are an approximate measure of the oxidation state of the absorbing atom, it is important to recognize that the correlation of XAS edge energy with effective nuclear charge is not direct. This result is finally applied to the question of quantitative sulfur speciation in complex materials of chemical, biological, or geological origin.     

Synthesis,Chiroptical Properties and Density Functional Theory Calculations of 3,3’‐Biphenyl‐2,2’‐BiTropone

The synthesis of new bitropone derivatives, namely, 3,3'‐biphenyl‐2,2'‐bitropone and 7,7’‐biphenyl‐2,2'‐bitropone, are reported. Isolation of enantiomers arising from restricted rotation around the C‐C bond connecting the tropone moieties was attempted by means of chiral high performance liquid chromatography (HPLC). No separation was obtained for 7,7’‐biphenyl‐2,2'‐bitropone. For 3,3'‐biphenyl‐2,2'‐bitropone, difficulties were encountered because of the low separation factor of the peaks and the presence of a rapid racemization process. However, quantitative chiroptical data on the antipodes were obtained by linking a circular dichroism (CD) spectrometer and a UV–vis spectrophotometric detector in series to the HPLC instrument. The analysis of the CD and UV–vis spectra in terms of absolute conformations was done with the help of theoretical calculations performed at the Density Functional Theory (DFT) level. The most stable conformations of the 3,3'‐biphenyl‐2,2'‐bitropone in its ground state were obtained. Starting from these minimum energy conformations, it was possible to compute theoretical CD and UV absorption spectra that fit well with the experimental ones. From this comparison the absolute configuration to the antipodes was assigned. Finally, the effect of the presence of the two lateral phenyl substituents on the structure of the bitropone and hence on the CD spectrum is discussed. Chirality 25:648–655, 2013. © 2013 Wiley Periodicals, Inc.     

Theoretical study on the optical response behavior to hydrogen chloride gas of a series of Schiff-base-based star-shaped structures

Schiff-base compounds have many applications in the field of optoelectronic materials and chemical sensing because of their appealing coordination ability, and simple and easily accessible use in structural modification. Herein, five kinds of star-shaped Schiff-base compounds were designed and their optical response behavior to hydrogen chloride (HCl) gas was studied using dependent/time-dependent density functional theory (DFT/TDDFT). Moreover, the relationship between structures and properties was investigated upon changing the benzene group into N atom or triazine group at the core-position and introducing a methoxyl (–OCH₃) or nitro (–NO₂) group into the star-shaped Schiff-bases at the tail of the branches. The results show that all five Schiff-bases could be candidates for HCl gas sensing materials. Furthermore, introducing an electron-donating group at either the core or the tail forms a charge transfer channel with the electron deficient H-bonded imino group, which is convenient for charge transfer and subsequently promotes a red-shift in absorption spectra and fluorescence quenching.     

Microsolvation effect and hydrogen-bonding pattern of taurine-water TA-(H2O)n (n = 1-3) complexes

The microsolvation of taurine (TA) with one, two or three water molecules was investigated by a density functional theory (DFT) approach. Quantum theory of atoms in molecules (QTAIM) analyses were employed to elucidate the hydrogen bond (H-bond) interaction characteristics in TA-(H₂O)_n (n = 1–3) complexes. The results showed that the intramolecular H-bond formed between the hydroxyl and the N atom of TA are retained in most TA-(H₂O)_n (n = 1–3) complexes, and are strengthened via cooperative effects among multiple H-bonds from n = 1–3. A trend of proton transformation exists from the hydroxyl to the N atom, which finally results in the cleavage of the origin intramolecular H-bond and the formation of a new intramolecular H-bond between the amino and the O atom of TA. Therefore, the most stable TA-(H₂O)₃ complex becomes a zwitterionic complex rather than a neutral type. A many-body interaction analysis showed that the major contributors to the binding energies for complexes are the two-body energies, while three-body energies and relaxation energies make significant contributions to the binding energies for some complexes, whereas the four-body energies are too small to be significant.     

Experimental and theoretical study on the structure and electronic spectra of imiquimod and its synthetic intermediates

Crystal structure of the imiquimod has been determined by single crystal X-ray analysis, imiquimod crystallizes in orthorhombic space group P2(1)2(1)2(1) and the molecules are linked along the c axis by the strong N-H ... N hydrogen bonds. A density functional theory (DFT) study on the electronic properties of imiquimod and its synthetic intermediates has been performed at B3LYP/6-31G* level, while taking solvent effects into account. Both the single configuration interaction (CIS) method and the time-dependent DFT (TDDFT) approaches have been used to calculate the electronic absorption spectra, and there is a good agreement between the calculated and experimental UV-visible absorption spectra. The fluorescence emission spectra of these three compounds in solution have also been measured, the relatively low fluorescence intensity is attributed to a chlorine-modulated heavy atom effect that enhances intersystem crossing between excited singlet and triplet states, and the relatively high fluorescence intensity of imiquimod results from an extended pi-conjugated system which enhances S(1)-->S(0) radiant transition.     

Enzymic racemization of allantoin

Allantoin racemase was isolated from cells of Candida utilis, and purified by chromatography on columns of DEAE-cellulose and Sephadex G-100. Using this purified enzyme, the racemization of allantoin in deuterium oxide was investigated. Polarimetric and PMR spectroscopic analyses showed that racemization of allantoin by the enzyme proceeded in parrallel with release of the hydrogen atom (5-H) attached to the asymmetric carbon (C-5) of allantoin. Non-enzymic racemization of allantoin, which was examined for comparison, however, was accompanied by much less or almost no release of allantoin 5-H. This indicates that the mechanism of racemization by the enzyme differs from that of non-enzymic racemization.     

Effect of H-bonding on the ambivalence of SCN towards copper(II)

Condensations of 2-(2-aminoethyl)pyridine with 4-methylimidazole-5-carboxaldehyde and 1-methyl-2-imidazolecarboxaldehyde generate the tridentate N donor ligands L and L′ respectively. Reactions of Cu(NCS)₂ with L and L′ yield respectively CuL(SCN)(NCS) (1) containing a CuN₄S core and CuL′(NCS)₂ (2) having a CuN₅ core. Both the cores are square pyramidal with SCN⁻ bound in 1 at the axial position through the S end. This differential behaviour of SCN⁻ in the two complexes despite the ligands being very similar, is investigated by DFT calculations at the B3LYP/TZV level. It is found that DFT calculations predict isolation of the Cu(ligand)(NCS)₂ species for both the ligands L and L′. Presence of an offsetting intermolecular H-bonding between the N atom of the thiocyanate and the N-H proton of the ligand L of an adjacent molecule makes the binding of SCN⁻ via the S end feasible in 1 resulting in the H-bonded dimer Cu₂L₂(SCN)₂(NCS)₂. The strength of the H-bond is estimated as 27.1 kJ mol⁻¹ from the DFT calculations. The question of such H-bonding does not arise with L′ as it lacks in a similar H atom. Dimeric 1 represents a case of two non-interacting spins.     

Activation of Ni Particles into Single Ni–N Atoms for Efficient Electrochemical Reduction of CO2

Electrochemical reduction of carbon dioxide (CO₂) to fuels and value‐added industrial chemicals is a promising strategy for keeping a healthy balance between energy supply and net carbon emissions. Here, the facile transformation of residual Ni particle catalysts in carbon nanotubes into thermally stable single Ni atoms with a possible NiN₃ moiety is reported, surrounded with a porous N‐doped carbon sheath through a one‐step nanoconfined pyrolysis strategy. These structural changes are confirmed by X‐ray absorption fine structure analysis and density functional theory (DFT) calculations. The dispersed Ni single atoms facilitate highly efficient electrocatalytic CO₂ reduction at low overpotentials to yield CO, providing a CO faradaic efficiency exceeding 90%, turnover frequency approaching 12 000 h^?1, and metal mass activity reaching about 10 600 mA mg^?1, outperforming current state‐of‐the‐art single atom catalysts for CO₂ reduction to CO. DFT calculations suggest that the Ni@N₃ (pyrrolic) site favors *COOH formation with lower free energy than Ni@N₄, in addition to exothermic CO desorption, hence enhancing electrocatalytic CO₂ conversion. This finding provides a simple, scalable, and promising route for the preparation of low‐cost, abundant, and highly active single atom catalysts, benefiting future practical CO₂ electrolysis.     

Structure and bonding of gold(I) and gold(III) nucleosides studied by 197Au Mössbauer spectroscopy

¹⁹⁷Au Mössbauer spectra of the series of complexes of gold(I), Au(nucl)₂Cl and gold(III), Au(nucl)Cl₃, Au(nucl - H⁺)Cl₂ and Au(nucl)₂Cl₃ were measured at 4.2 K, (nucl = nucleoside, e.g. guanosine(guo), inosine(ino), triacetylguanosine-(trguo) and triacetylinosine(trino)). It is concluded from the spectra that the gold(I) nucleosides have linear ClAuN coordination, with one coordinated nucleoside molecule per gold(I) ion, bound via the N(7) atom. The σ-donor strength of the guo ligand is somewhat higher than that of the ino ligand. The complexes Au(ino)Cl₃ and Au(guo)Cl₃, in the series Au(nucl)Cl₃, have significantly higher IS and QS values than the corresponding complexes with the triacetylnucleosides, Au(trino)Cl₃ and Au(trguo)Cl₃. This may be explained by a weak O(6)-interaction with gold(III), in a nearly trigonal bipyramidal configuration in the former case and by the presence of the strongly electron withdrawing acetyl groups in the latter, which reduces the donor strength of their N(7) atoms. The complexes of the Au(nucl - H⁺)Cl₂ series all appear to have a polymeric structure. The gold(III) ion is bound to the N(7) atom and the O(6) or the N(1) atom of the nucleosides. Finally, the Mössbauer spectra of the series Au(nucl)₂)Cl₃ can only be explained by assuming approximately octahedral AuN₂Cl₄ structures, with bridging chlorine atoms.     

Probing the geometric and electronic structures of the low-temperature azide adduct and the product-inhibited form of oxidized manganese superoxide dismutase

The geometric and electronic structures of the six-coordinate azide adduct of oxidized manganese superoxide dismutase (Mn3+ SOD) that is formed at low temperatures, LT N3-Mn3+ SOD, has been examined in detail through a combined spectroscopic/computational approach. Electronic absorption, circular dichroism (CD), magnetic CD (MCD) and variable-temperature, variable-field (VTVH) MCD spectroscopies were used to determine electronic transition energies and to obtain an estimate of zero-field splitting parameters for LT N3-Mn3+ SOD. These experimental data were utilized in conjunction with semiempirical intermediate neglect of differential overlap/spectroscopic parametrization-configuration interaction (INDO/S-CI) and time-dependent density functional theory (TD-DFT) computations to evaluate hypothetical active-site models of LT N3-Mn3+ SOD generated by constrained DFT geometry optimizations. Collectively, our spectroscopic/computational results indicate that N3- binding to Mn3+ SOD at low temperatures promotes neither protonation of the axial solvent ligand nor reorientation of the redox-active molecular orbital, both of which had been previously suggested. Using the same experimentally validated computational approach, models of the product-inhibited form of MnSOD were also developed and evaluated by their relative energies and TD-DFT-computed absorption spectra. On the basis of our computational results as well as previously published kinetic data, we propose that the product-inhibited form of MnSOD is best described as a side-on peroxo-Mn3+ adduct possessing an axial H2O ligand. Notably, attempts to generate a stable hydroperoxo-Mn3+ SOD species by protonation of the proximal O atom of the hydroperoxo ligand resulted in dissociation of HOO- and eventual H+ transfer from Tyr34 to HOO-, generating deprotonated Tyr34 and H2O2. The implications of these results with respect to the mechanism of O2*- dismutation by MnSOD are discussed.     

New thiocyanato and azido adducts of the redox-active Fe(η-C5Me5)(η-dppe) center: Synthesis and study of the Fe(II) and Fe(III) complexes

The new thiocyanato- (5) and azido- (6) complexes were synthesized and studied under their Fe(II) and Fe(III) redox states. For the first time among the various [Fe(η⁵-C₅Me₅)(η²-dppe)]-based cationic radicals studied so far, the magnitude and spatial orientation of the g-tensor diagonal values were experimentally determined for 5[PF₆]. These data are in good agreement with those issued from a DFT modelization. The changes experienced by the electronic structure of the Fe(II) complexes subsequent to oxidation are reminiscent of these previously observed for the known arylalkynyl analogues, albeit some differences can be pointed out. Thus, the differences observed in the ¹H NMR spectra of 5[PF₆] and 6[PF₆] are attributed to a slower electronic spin relaxation and to the differently oriented magnetic anisotropy. The sizeable spin density evidenced by DFT on the terminal atom of the ligands of the Fe(III) complexes renders these new paramagnetic metallo-ligands quite appealing for accessing larger polynuclear molecular assemblies with magnetically interacting centers.     

Alkylation of nucleic acid components with ethylenimine and its derivatives. IV. Alkylation of homopolynucleotides and DNA]

Alkylation of homopolynucleotides and DNA by thio TEPA and monoaziridine diethyl phosphate was studied. The modification affected nucleic bases and terminal phosphate groups but not internucleotide phosphate groups. It was shown that the main center of modification in poly(A) was the N1 atom, whereas the products of N6- and N3-alkylations were formed in smaller amounts. In poly(G), the alkylation proceeded predominantly at the N7 and, insignificantly, at the N1 atom of guanine; the pyrimidine N3 atom is alkylated poorly in poly(C) and even worse in poly(U). In the case of DNA, the major alkylated sites are the guanine N7 and the adenine N3; this results in DNA denaturation and the subsequent formation of products modified at N1 and N6 of adenine, N1 of guanine, and N3 of cytosine. An increase in the pH and ionic strength of the solution as well as the DNA denaturation decrease the reaction rate, whereas ultrasonic fragmentation enhances it. Upon alkylation, melting temperatures decrease, CD and UV spectra change, and DNA luminescence appears. To separate the reaction mixtures and identify the DNA alkylation products, chemical hydrolysis, ion-exchange and reverse-phase HPLC, and UV spectroscopy were used.     

Synthesis and characterization of some aminoarsonium chlorides

R₃As reacts with NR′R″Cl to give good yields of a new homologous series of aminoarsonium chlorides, [R₃AsNR′R″]Cl, in which R = Me, Et, n-Pr, and Ph; R′ and/or R″ = H, Me. IR, NMR, mass, and X-ray spectral data suggest that the arsenic is tetra- coordinate. Electfical conductivity and temperature and concentration dependent NMR studies suggest that hydrogen-bonding interactions are important in solution. Quaternization of the arsenic produces a downfield ¹H NMR chemical shift for the protons in the alkyl chains and a change from non-equivalence to equivalence of the C-1 protons. The NMR data are compared with those for the analogous phosphorus compounds. The electron impact, chemical ionization, and negative ion mass spectral data and fragment ion identities are given for the compounds. Ions corresponding to a variety of AsCl containing species, in addition to those associated .with fragmentation of the R₃As moieties, are observed in the EI mass spectra. AsN, AsNAs, and AsNAsN containing fragments are observed in the Cl mass spectra and AsCl bonding species in the NI mass spectra. A preliminary X-ray diffraction study of [n-Pr₃AsNH₂]Cl indicates near tetrahedral geometry about the arsenic atom.     

The insertion reactions of the p-complex silylenoid H<Subscript>2</Subscript>SiLiF with Si-X (X=F,Cl, Br,O, N) bonds

The insertion reactions of the silylenoid H₂SiLiF with SiH₃XH_n-1 (X = F, Cl, Br, O, N; n = 1, 1, 1, 2, 3) have been studied by DFT calculations. The results indicate that the insertions proceed in a concerted manner, forming H₃SiSiH₂XH_n-1 and LiF. The essence of H₂SiLiF insertion into Si-X bonds reactions are the donations of the electrons of X into the p orbital on the Si atom in H₂SiLiF and the σ electrons on the Si atom in H₂SiLiF to the positive SiH₃ group. The order of reactivity by H₂SiLiF insertion in vacuum indicates the reaction barriers decrease for the same-row element X from right to left and the same-family element X from up down in the periodic table. The insertion reactions in ether are similar to those in vacuum. The energy barriers in vacuum are higher than those in ether. The silylenoid insertions are thermodynamically exothermic both in vacuum and in ether.     

Conformational states of N-acylalanine dithio esters: correlation of resonance Raman spectra with structures

The conformational states of N-acylalanine dithio esters, involving rotational isomers about the RC(=O)NH--CH(CH3) and NHCH(CH3)--C(=S) bonds, are defined and compared to those of N-acylglycine dithio esters. The structure of N-(p-nitrobenzoyl)-DL-alanine ethyl dithio ester has been determined by X-ray crystallographic analysis; it is a B-type conformer with the amide N atom cis to the thiol sulfur. Raman and resonance Raman (RR) measurements on this compound and for the B conformers of solid N-benzoyl-DL-alanine ethyl dithio ester and N-(beta-phenylpropionyl)-DL-alanine ethyl dithio ester and its NHCH(CD3)C(=S) and NHCH(CH3)13C(=S) analogues are used to set up a library of RR data for alanine-based dithio esters in a B-conformer state. (Methyloxycarbonyl)-L-phenylalanyl-L-alanine ethyl dithio ester crystallizes in an A-like conformational state wherein the alanine N atom is nearly cis to the thiono S atom (C=S) [Varughese, K.I., Angus, R.H., Carey, P.R., Lee, H., & Storer, A.C. (1986) Can. J. Chem. 64, 1668-1673]. RR data for this solid material in its isotopically unsubstituted and CH(C-D3)C(=S) and CH(CH3)13C(=S) forms provide information on the RR signatures of alanine dithio esters in A-like conformations. RR spectra are compared for the solid compounds, for N-(p-nitrobenzoyl)-DL-alanine, N-(beta-phenylpropionyl)-DL-alanine, and (methyloxycarbonyl)-L-phenylalanyl-DL-alanine ethyl dithio esters, and for several 13C=S- and CD3-substituted analogues in CCl4 or aqueous solutions. The RR data demonstrate that the alanine-based dithio esters take up A, B, and C5 conformations in solution.(ABSTRACT TRUNCATED AT 250 WORDS)     

EPR and H NMR spectroscopy and DFT study of pentaammineruthenium(III)phenylcyanamide complexes

The EPR and ¹H NMR spectroscopy of seven [Ru(NH₃)₅L]²⁺ complexes, where L = 3,5-dimethoxyphenylcyanamide (MeO₂pcyd), 3,4,5-trimethoxyphenylcyanamide (MeO₃pcyd), 4-nitrophenylcyanamide (NO₂pcyd), 2,3-dichlorophenylcyanamide (Cl₂pcyd), 2,4,6-trichlorophenylcyanamide (Cl₃pcyd), 2,3,5,6-tetrachlorophenylcyanamide (Cl₄pcyd) and pentachlorophenylcyanamide (Cl₅pcyd), was performed. EPR spectra of the complexes showed an axial signal with g_|| and g_⊥ at high and low field, respectively. The g_|| axis is suggested to lie along the Ru-cyanamide bond. Gas-phase DFT calculations of [Ru(NH₃)₅ phenylcyanamide]²⁺ showed spin density localized mostly on the phenylcyanamide ligand, in disagreement with EPR data. DFT/polarizable continuum model (PCM, water solvation) calculations shifted spin density towards ruthenium so that spin density was shared between ruthenium and phenylcyanamide ligand. Proton contact shifts were determined from NMR and EPR data and were used to estimate spin density distributions on phenyl ring carbons. The results showed that the DFT/PCM calculation overestimated spin density on phenyl ring carbons by approximately one order of magnitude. Donor-acceptor interactions between the solute and solvent that are not fully accounted for in the DFT/PCM method are suggested to stabilize the Ru(III) oxidation state.     

95Mo NMR studies of complexes containing the Mo2O52+ core and crystal structure of Mo2O5[SC6H4NHCH2C5H4N]2(C3H7NO)3

The crystal structure of Mo₂O₅[SC₆H₄NHCH₂C₅H₄N]₂(C₃N₇NO)₃ is reported and seen to consist of a single oxo-bridged species with each Mo atom bonded to cis dioxo groups and the nitrogen atoms and thiolate group of the tridentate ligand. ⁹⁵Mo NMR spectra of this and three related complexes are presented and attempts made to interpret them in terms of their crystal structures.