Cluster oxalate complexes [M3(mu3-Q)(mu2-Q2)3(C2O4)3]2- and [Mo3(mu3-Q)(mu2-Q)3(C2O4)3(H2O)3]2- (M = Mo, W; Q = S, Se): mechanochemical synthesis and crystal structure

Mechanochemical reaction of cluster coordination polymers 1infinity[M3Q7Br4] (M = Mo, W; Q = S, Se) with solid K2C2O4 leads to cluster core excision with the formation of anionic complexes [M3Q7(C2O4)3]2-. Extraction of the reaction mixture with water followed by crystallization gives crystalline K2[M3Q7(C2O4)3].0.5KBr.nH2O (M = Mo, Q = S, n = 3 (1); M = Mo, Q = Se, n = 4 (2); M = W, Q = S, n = 5 (3)). Cs2[Mo3S7(C2O4)3].0.5CsCl.3.5H2O (4) and (Et4N)1.5H0.5K{[Mo3S7(C2O4)3]Br}.2H2O (5) were also prepared. Close Q...Br contacts result in the formation of ionic triples {[M3Q7(C2O4)3](2)Br}5- in 1-4 and the 1:1 adduct {[Mo3S7(C2O4)3]Br}3- in 5. Treatment of 1 or 2 with PPh(3) leads to chalcogen abstraction with the formation of [Mo3(mu3-Q)(mu2-Q)3(C2O4)3(H2O)3]2-, isolated as (Ph4P)2[Mo3(mu3-S)(mu2-S)3(C2O4)3(H2O)3].11H2O (6) and (Ph4P2[Mo3(mu3-Se)(mu2-Se)3(C2O4)3(H2O)3].8.5H2O.0.5C2H5OH (7). All compounds were characterized by X-ray structure analysis. IR, Raman, electronic, and 77Se NMR spectra are also reported. Thermal decomposition of 1-3 was studied by thermogravimetry.     

Rate coefficients for the reaction of OH with (E)-2-pentenal, (E)-2-hexenal, and (E)-2-heptenal

Rate coefficients for the gas-phase reaction of the OH radical with (E)-2-pentenal (CH(3)CH(2)CH[double bond]CHCHO), (E)-2-hexenal (CH(3)(CH(2))(2)CH[double bond]CHCHO), and (E)-2-heptenal (CH(3)(CH(2))(3)CH[double bond]CHCHO), a series of unsaturated aldehydes, over the temperature range 244-374 K at pressures between 23 and 150 Torr (He, N(2)) are reported. Rate coefficients were measured under pseudo-first-order conditions in OH with OH radicals produced via pulsed laser photolysis of HNO(3) or H(2)O(2) at 248 nm and detected by pulsed laser-induced fluorescence. The rate coefficients were independent of pressure and the room temperature rate coefficients and Arrhenius expressions obtained are (cm(3) molecule(-1) s(-1) units): k(1)(297 K)=(4.3 +/- 0.6)x 10(-11), k(1)(T)=(7.9 +/- 1.2)x 10(-12) exp[(510 +/- 20)/T]; k(2)(297 K)=(4.4 +/- 0.5)x 10(-11), k(2)(T)=(7.5 +/- 1.1)x 10(-12) exp[(520 +/- 30)/T]; and k(3)(297 K)=(4.4 +/- 0.7)x 10(-11), k(3)(T)=(9.7 +/- 1.5)x 10(-12) exp[(450 +/- 20)/T] for (E)-2-pentenal, (E)-2-hexenal and (E)-2-heptenal, respectively. The quoted uncertainties are 2sigma(95% confidence level) and include estimated systematic errors. Rate coefficients are compared with previously published room temperature values and the discrepancies are discussed. The atmospheric degradation of unsaturated aldehydes is also discussed.     

Spectrophotometric studies on ion-pair extraction equilibria of the iron(ii) and iron(III) complexes with 4-(2-pyridylazo)resorcinol

The ion-pair extraction equilibria of the iron(II) and iron(III) chelates of 4-(2-pyridylazo)resorcinol (PAR, H(2)L) are described. The anionic chelates were extracted into chloroform with benzyldimethyltetradecylammonium chloride (QC1) as counter-ion. The extraction constants were estimated to be K(ex1)(Fe(II)) = [Q{Fe(II)(HL)L}](0)/[Q(+)][{Fe(II)(HL)L}(-)] = 10(8.59 +/- 0.11), K(ex2)(Fe(II)) = [Q(2){Fe(II)L(2)}](o)/ [Q(+)](2)[{Fe(II)L(2)}(2-)] = 10(12.17 +/- 0.10) and K(ex1)(Fe(III)) = [Q{Fe((III))L(2)}](o)/(Q(+)][{Fe(III)L(2)}(-)] = 10(6.78 +/- 0.15) at I = 0.10 and 20 degrees , where [ ](o) is concentration in the chloroform phase. Aggregation of Q{Fe(III)L(2)} in chloroform was observed and the dimerization constant (K(d) = [Q(2){Fe(III)L(2)}(2)](o)/[Q{Fe(III)L(2)}](o)(2)) was evaluated as log K(d) = 4.3 +/- 0.3 at 20 degrees . The neutral chelates of {Fe(II)(HL)(2)} and {Fe(III)(HL)L}, and the ion-pair of the cationic chelate, {Fe(III)(HL)(2)}ClO(4), were also extracted into chloroform or nitrobenzene. The relationship between the forms and extraction properties of the iron(II) and iron(III) PAR chelates are discussed in connection with those of the nickel(II) and cobalt(III) complexes. Correlation between the extraction equilibrium data and the elution behaviour of some PAR chelates in ion-pair reversed-phase partition chromatography is also discussed.     

Synthesis of 2-substituted (+/-)-(2r,3r,5r)-tetrahydrofuran-3,5-dicarboxylic acid derivatives

An efficient synthesis of 2-substituted (+/-)-(2R,3R,5R)-tetrahydrofuran-3,5-dicarboxylic acid derivatives has been developed. Starting from 5-norborne-2-ol, the key intermediate (+/-)-methyl 5,6-exo,exo-(isopropylidenedioxy)-2-oxabicyclo[2.2.1]heptane-3-exo-carboxylate (15) was synthesized in an efficient six-step sequence. The key transformation is the base-catalyzed methanolysis-rearrangement of (+/-)-6,7-exo,exo-(isopropylidenedioxy)-4-exo-iodo-2-oxabicyclo[3.2.1]octan-3-one (14). Further manipulation of the 3-substituent of (+/-)-methyl 5,6-exo,exo-(isopropylidenedioxy)-2-oxabicyclo[2.2.1]heptane-3-exo-carboxylate (15) followed by deprotection of the diol moiety and ring opening catalyzed by RuCl(3)/NaIO(4) gave the title compounds in good yield.     

A study of the sequential acid-catalyzed hydroxylation of dodecahydro-closo-dodecaborate(2-)

The closo-[B12H12-n(OH)n]2- (n = 1-4) ions have been synthesized by the reaction of cesium dodecahydro-closo-dodecaborate(2-), Cs21, with aqueous sulfuric acid. Variation of the reaction temperature, time, and acid concentration results in the stepwise introduction of from one to four hydroxyl groups. Each individual hydroxylation step proceeds regioselectively, affording only one isomer per step. Further substitution of the hydroxylated cluster preferentially takes place at a B-H vertex meta to a B-OH vertex. The closo-[B12H12-n(OH)n]2- (n = 1-4) species, designated 2-5, respectively, are characterized by one- and two-dimensional 11B NMR spectroscopy, IR spectroscopy, and high-resolution fast atom bombardment (FAB) mass spectrometry. A rationale that qualitatively explains the influence of the hydroxyl group on the chemical shifts of the individual boron vertices is developed. Furthermore, the solid state structures of closo-[B12H11(OH)]2-, 2, and closo-1,7-[B12H10(OH)2]2-,3, are determined by X-ray diffraction. Crystallographic data are as follows: For [MePPh3](2)2, monoclinic, space group P2(1)/n, a = 890.1(5) pm, b = 1814(1) pm, c = 1270.5(7) pm, beta = 101.66(2) degrees, Z = 2, R = 0.055; for [MePPh3](2)3, monoclinic, space group P2(1)/n, a = 887.6(4) pm, b = 1847.2(8) pm, c = 1271.1(5) pm, beta = 101.17(1) degrees, Z = 2, R = 0.065. In addition, synthetic routes to O-derivatized species of the anions 2-5 such as closo-[B12H11(OTiCpCl2)]2-, 7, closo-1,7-[B12H10(OTiCpCl2)2]2-, 8, closo-1,7,9-[B12H9(OTiCpCl2)3]2-, 9, closo-[B12H11(OCONHPh)]2-, 10, and closo-1,7-[B12H10(OSO2Me)2]2-, 11, are described. The crystal structures of 7 and 11 are determined by single-crystal X-ray diffraction. Crystallographic data are as follows: For [MePPh3](2)7, monoclinic, space group Cc, a = 2530.5(2) pm, b = 1653.3(1) pm, c = 1281.3(1) pm, beta = 118.79(2) degrees, Z = 4, R = 0.085; for [HPy](2)11, monoclinic, space group P2(1)/n, a = 1550.9(8) pm, b = 993.1(5) pm, c = 1726.5(9) pm, beta = 112.36(2) degrees, Z = 4, R = 0.061.     

The (SO2)2N3- anion

The recently proposed (SO2)2N3- anion was structurally characterized by single-crystal X-ray diffraction of the [Cs][(SO2)2N3] salt (P2(1)/c, a = 8.945(2) A, b = 10.454(2) A, c = 8.152(2) A, beta = 109.166(3) degrees, Z = 4, and R1 = 0.0329 at 130 K). In the (SO2)2N3- anion, both SO2 ligands are coordinated to one terminal nitrogen atom of the N3- anion.     

New 3-（4-arylpiperazin-1-yl）-1-（benzo[b]thiophen-3-yl）-2-methylpropanol derivatives：Synthesis and evaluation for dual 5-HT1A/SSRI activities

A series of 3-（4-arylpiperazin-1-yl）-1-（benzo[b]thiophen-3-yl）-2-methylpropanol derivatives were designed and synthesized based on 5-HT1A/SSRI drugs design strategies.The synthesized compounds were evaluated for their dual 5-HT1A/5-HTT activities.     

2'-O-[2-(amino)-2-oxoethyl] oligonucleotides

[structure: see text] Oligonucleotides with novel modifications, 2'-O-[2-(amino)-2-oxoethyl] (2'-O-NAc), 2'-O-[2-(methylamino)-2-oxoethyl] (2'-O-NMAc), 2'-O-[2-(dimethylamino)-2-oxoethyl] (2'-O-DMAc), and 2'-O-[2-[[2-(dimethylamino)ethyl]amino]-2-oxoethyl] (2'-O-DMAEAc), have been synthesized. These modified oligonucleotides exhibit high binding affinity to complementary RNA (and not to DNA) and considerably enhance the nuclease stability of oligonucleotides with t(1/2) > 24 h.     

Comparison of oxygen and sulfur effects on keto-enol chemistry in benzolactone systems: benzo[b]-2,3-dihydrofuran-2-one and -2-thione and benzo[b]-2,3-dihydrothiophene-2-one and -2-thione

Carbon-acid ionization constants, Q(K)(a)(concentration quotient at ionic strength = 0.10 M), were determined by spectrophotometric titration in aqueous solution for benzo[b]-2,3-dihydrofuran-2-one (3, pQ(K)(a) = 11.87), benzo[b]-2,3-dihydrothiophene-2-one (2, pQ(K)(a) = 8.85), and benzo[b]-2,3-dihydrofuran-2-thione (1, pQ(K)(a) = 2.81). Rates of approach to keto-enol equilibrium were also measured for the latter two substrates in perchloric acid, sodium hydroxide, and buffer solutions, and the rate profiles constructed from these data gave the ionization constants of the enols ionizing as oxygen or sulfur acids pQ(E)(a) = 5.23 for 2 and pQ(E)(a) = 2.69 for 1. Combination of these acidity constants with the carbon-acid ionization constants according to the relationship Q(K)(a)/Q(E)(a) = K(E) then gave the keto-enol equilibrium constants pK(E) = 3.62 for 2 and pK(E) = 0.12 for 1. The fourth, all-sulfur, member of this series, benzo[b]-2,3-dihydrothiophene-2-thione (4), proved to exist solely as the enol in aqueous solution, and only the enol ionization constant pQ(E)(a) = 3.44 could be determined for this substance; the limits pK(E) < 1.3 and pQ(K)(a) < 2.1, however, could be set. The unusually high acidities and enol contents of these substances are discussed, as are also the relative values of the ketonization and enolization rate constants measured; in the latter cases, Marcus rate theory is used to determine intrinsic kinetic reactivities, free of thermodynamic effects.     

Mononuclear (Pd, Pt), heterodinuclear (PdAg, PtAg), and tetranuclear (Pd2Ag2, Pt2Ag2) 1,1-ethylenedithiolato complexes

lp;&-5q;1 The reactions of [Tl2[S2C=C[C(O)Me]2]]n with [MCl2L2] (1:1) or with [MCl2(NCPh)2] and PPh3 (1:1:2) give complexes [M[eta2-S2C=C[C(O)Me]2]L2] [M = Pt, L2 = 1,5-cyclooctadiene (cod) (1); L2 = bpy, M = Pd (2a), Pt (2b), L = PPh3, M = Pd (3a), Pt (3b)] whereas with MCl2 and QCl (2:1:2) anionic derivatives Q2[M[eta2-S2C=C[C(O)Me]2]2] [M = Pd, Q = NMe4 (4a), Ph3P=N=PPh3 (PPN) (4a'), M = Pt, Q = NMe4 (4b)] are produced. Complexes 1 and 3 react with AgClO4 (1:1) to give tetranuclear complexes [[ML2]2Ag2[mu2,eta2-(S,S')-[S2C=C[C(O)Me]2]2]](ClO4)2 [L = PPh3, M = Pd (5a), Pt (5b), L2 = cod, M = Pt (5b')], while the reactions of 3 with AgClO4 and PPh3 (1:1:2) give dinuclear [[M(PPh3)2][Ag(PPh3)2][mu2,eta2-(S,S')-S2C=C[C(O)Me]2]]]ClO4 [M = Pd (6a), Pt (6b)]. The crystal structures of 3a, 3b, 4a, and two crystal forms of 5b have been determined. The two crystal forms of 5b display two [Pt(PPh3)2][mu2,eta2-(S,S')-[S2C=C[C(O)Me]2]2] moieties bridging two Ag(I) centers.     

Structure and reactivity of trans-bis[2-(2-chloroethyl)pyridine]palladium chloride (1). A study on the elimination reaction of 1 and 2-(2-chloroethyl)pyridine induced by quinuclidine in acetonitrile

[reaction: see text] The trans-bis[2-(2-chloroethyl)pyridine]palladium chloride (1) has been prepared and structurally characterized by X-ray spectroscopy and computational study. The X-ray structure of 1 is consistent with the trans isomer (with respect to Pd). The NMR spectrum and the computational study are in agreement with an equilibrium in CD3CN solution between two isomers of the trans structure. The reaction of the palladium complex with quinuclidine in CH3CN, at 25 degrees C, leads to competing elimination and displacement reactions with formation of vinylpyridine and chloroethylpyridine in a ratio of 1.5:1. However, the rate constant for formation of uncoordinated (vinyl)pyridine monitored by HPLC (kQ(HPLC) = 2.3 x 10(-3) M(-1) s(-1)) is nearly 3 times slower than a rate constant monitored spectrophotometrically (kQ = 6.5 x 10(-3) M(-1) s(-1)). This suggests that the initial product of elimination is a palladium complex of vinylpyridine and that displacement from this complex is partially rate determining in the formation of the uncoordinated product. A study by UV spectroscopy at lambda = 295 nm of trans-bis[2-(2-chloroethyl)pyridine-d2]palladium chloride with quinuclidine (Q) has shown the presence of a significant primary kinetic isotope effect, kQ(H)/kQ(D) = 1.8, for the elimination reaction within the Pd complex, 1. The second-order rate constant for the beta-elimination reaction from 2-(2-chloroethyl)pyridine induced by quinuclidine in CH3CN at 25 degrees C is kQ(FREE) = 6.2 x 10(-6) M(-1) s(-1). It can be observed as a significant activation (about 3 orders of magnitude) of the beta-elimination reaction within the complex 1 with respect to the free 2-(2-chloroethyl)pyridine. The possible mechanism in agreement with these results is discussed.     

Cucurbituril binding of trans-[{PtCl(NH3)2}2(micro-NH2(CH2)8NH2)]2+ and the effect on the reaction with cysteine

The effect of encapsulation by cucurbiturils Q[7] and Q[8] on the rate of reaction of the anti-cancer dinuclear platinum complex trans-[{PtCl(NH3)2}2(micro-NH2(CH2)8NH2)]2+ with the model biological nucleophiles glutathione and cysteine has been examined by NMR spectroscopy. It was expected that the octamethylene linking chain would fold inside the cucurbituril host and hence position the reactive platinum centres close to the cucurbituril portals, and thereby, confer resistance to degradation by biological nucleophiles. The upfield shifts of the resonances from the methylene protons in the linking ligand observed in 1H NMR spectra of the platinum complex upon addition of either Q[7] or Q[8] indicate that the cucurbituril is positioned over the linking ligand, with the Pt(II) centres projecting out of the portal. Furthermore, the relative changes in chemical shift of the methylene resonances suggest that the octamethylene linking chain folds within the cucurbituril cavity, particularly in Q[8]. Simple molecular models, based on the observed relative changes in chemical shift, could be constructed that were consistent with the proposed folding of the linking ligand within the cucurbituril cavity. Encapsulation by Q[7] was found to reduce the rate of reaction of the platinum complex with glutathione. Encapsulation by Q[7] and Q[8] was also found to reduce the rate of reaction of the platinum complex with cysteine, with Q[8] slowing the reaction to a greater extent than Q[7], consistent with the inferred encapsulation geometries. Encapsulation of dinuclear platinum complexes within the cucurbituril cavity may provide a novel way of reducing the reactivity and degradation of these promising chemotherapeutic agents with blood plasma proteins.     

An unusual reaction of 2-(2-pyridylcarbonyl)- and 2-(2-quinolylcarbonyl)benzoyl chlorides with p-nitroaniline

In the reaction of 2-(2-pyridylcarbonyl)benzoyl chloride, which exists in the form of 6,11-dioxo-6,11dihydrobenzo[b]quinolizinium chloride, with p-nitroaniline, 2-(4-nitrophenylimino)-6, 11-dihydro-2H-benzo-[b]quinolizine-6, I I -dione is unexpectedly formed. When it reacts with water or methanol there is an opening of the quinolizine ring and aromatization of the quinoid fragment with the formation of 2-[4-(4nitrophenylamino)-2-pyridylcarbonyl]benzoic acid or its methyl ester. Under the action of antimony pentachloride, 2- 2-quinolylcarbonyl)benzoylchloride-3 (2-quinolyl)-3-chloro- 1, 3-dihydrobenzo[c]furan-1 -one -is converted to 3-(2-quinolyl)-1,3-dihydrobenzo[c]furan-1-on-3-ylium hexachlorantimonate, which undergoes isomerizing recyclization upon heating to 7,12-dioxo-7,12-dihydrobenzo[b/ hexachloroantimonate. The latter enters into an analogous reaction with p-nitroaniline, thereby forming 5-(4-nitrophenylimino)-7,12-dihydro-5H-dibenzo[b,f]quinolizine-7,2-dione.Riga Technical University, Riga LV-1048. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 938–944, July, 1995. Original article submitted May 31, 1995.     

Dipolar cycloaddition of ethyl isocyanoacetate to 3-chloro-2-(methylthio)/2-(methylsulfonyl)quinoxalines: highly regio- and chemoselective synthesis of substituted imidazo[1,5-a]quinoxaline-3-carboxylates

An efficient route for regio- and chemoselective synthesis of substituted 3-(carboethoxy)imidazo[1,5-a]quinoxalines and novel diimidazo[1,5-a:5',1'-c]quinoxalines via base-induced cycloaddition of ethyl isocyanoacetate to unsymmetrically substituted 3-chloro-2-(methylthio)/2-(methylsulfonyl)quinoxalines has been reported.     

An equilibrium analysis of the aqueous H+-MoO4(2-)-(HP)O(3)2- and H+-MoO4(2-)-(HP)O(3)2--HPO4(2-) systems

The speciation in the phosphitomolybdate system, H+-MoO4(2-)-(HP)O(3)2-, has been determined from combined potentiometric and 31P NMR measurements in 0.600 M Na(Cl) medium at 298(1) K. Potentiometric titration data were collected in the ranges 2.5<-log[H+]<6.2, 40.0相似文献   

2-(Phenyltelluromethyl)tetrahydrofuran (L) and 2-(2-{4-methoxyphenyl}telluroethyl)-1,3- dioxolane (L) and their palladium(II) and platinum(II) complexes

The nucleophile [ArTe⁻] generated in situ borohydride solution of Ar₂Te₂, reacts with 2-(chloromethyl) tetrahydrofuran and 2-(2-bromoethyl)-1,3-dioxolane resulting in L¹ and L², respectively. The complexes of palladium(II) and platinum(II) with L¹/L² having stoichiometries [MCl₂·L₂], [ML₂](ClO₄)₂, [(DPPE)ML₂](ClO)₄)₂, [(PPh₃)₂ML₂](ClO₄)₂ and [(phen)ML₂](ClO₄)₂ (where L = L¹/L² DPPE = Ph₂PC H₂CH₂PPh₂, PHEN = 1,10-phenanthroline and M = Pd/Pt) have been synthesized. IR, ¹H, ¹²⁵Te{¹H} and ³¹P{¹H} NMR and UV-vis spectral data of these species in conjunction with their molar conductance and molecular weight data have been used to authenticate the new species. In all complexes (1–20) the ligands L¹ and L² are coordinated through tellurium and in the complexes of formula [ML₂](ClO₄)₂ (M = Pd, Pt) the ligand is bidentate with the oxygen atom used in complexation. In solution, complexes PtCl₂L₂ exist as a mixture of cis and trans isomers whereas only the trans isomer was observed for the palladium analogues. The [(phen)PdL₂](ClO₄)₂(Q) quenches ¹O₂ readily. The plot of log [Q] vs time is linear. Mechanism compatible with the experimental observations is proposed.     

Preparation and properties of the full series of cuboidal clusters [Mo(x)W4-xSe4(H2O)12]n+ (n = 4-6) and their derivatives

Hydrothermal reactions between incomplete cuboidal cluster aqua complexes [M3Q4(H2O)9]4+ and M(CO)6 (M = Mo, W; Q = S, Se) offer easy access to the corresponding cuboidal clusters M4Q4. The complete series of homometal and mixed Mo/W clusters [Mo(x)W4-xQ4(H2O)12]n+ (x = 0-4, n = 4-6) has been prepared. Upon oxidation of the mixed-metal clusters, it is the W atom which is lost, allowing selective preparation of new trinuclear clusters [Mo2WSe4(H2O)9]4+ and [MoW2Se4(H2O)9]4+. The aqua complexes were converted by ligand exchange reactions into dithiophosphato and thiocyanato complexes, and crystal structures of [W4S4((EtO)2PS2)6], [MoW3S4((EtO)2PS2)6], [Mo4Se4((EtO)2PS2)6], [W4Se4((i-PrO)2PS2)6], and (NH4)6[W4Se4(NCS)12]-4H20 were determined. Cyclic voltammetry was performed on [Mo(x)W4-xCO4(H2O)12]n+, showing reversible redox waves 6+/5+ and 5+/4+. The lower oxidation states are more difficult to access as the number of W atoms increases. The [Mo2WSe4(H2O)9]4+ and [MoW2Se4(H2O)9]4+ species were derivatized into [Mo2WSe4(acac)3(py)3]+ and [MoW2Se4(acac)3(py)3]+, which were also studied by CV. When appropriate, the products were also characterized by FAB-MS and NMR (31P, 1H) data.     

Synthesis of (2S,3S)-[3-(2)H1]-4-methyleneglutamic acid and (2S,3R)-[2,3-(2)H2]-4-methyleneglutamic acid

(2S,3S)-[3-(2)H1]-4-Methyleneglutamic acid 1a and (2S,3R)-[2,3-(2)H2]-4-methyleneglutamic acid 1b have been synthesised for use in biosynthetic and metabolic studies.     

Preparation and magnetic properties of Mn(hfac)(2)-complexes of 2-(5-pyrimidinyl)- and 2-(3-pyridyl)-substituted nitronyl nitroxides

Mn(hfac)(2) complexes of [2-(5-pyrimidinyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H- imidazoline-1-oxyl 3-oxide] (1) and its 2-(3-pyridyl) analogue (2) were prepared. Both complexes formed similar dimer structures. However, their packing patterns were considerably different. The pyrimidine dimers were aligned to form a linear chain structure, and each dimer was weakly bound by two sets of O6-C2 short contacts. In the pyridine dimer complex, two structurally similar but independent dimers were alternatively arranged, and two dimer-dimer contacts, O6-C2 (3.13 A) and O6-C3 (3.30 A), were observed. The pyrimidine complex showed strong antiferromagnetic behavior in the high temperature region (150-300 K) and weak ferromagnetic behavior below 100 K. Two models were used to analyze these magnetic properties. One is a quintet-septet thermal equilibrium model with mean-field approximation, which can reproduce the round minimum observed at about 150 K in chi(p)T plots (J(1)/k(B) = -148 +/- 2 K with theta = +2.5 +/- 0.1 K). The other is a ferromagnetic S = 2 chain model to fit the chi(p)T values in the lower temperature region (J(S=2)/k(B) = +0.31 +/- 0.01 K). The pyridine complex showed antiferromagnetic interactions both in the high and low temperature regions. The magnetic behavior was similarly analyzed with the following parameters: J(1)/k(B) = -140 +/- 2 K with theta = -0.55 +/- 0.05 K, and J(S=2)/k(B) = -0.075 +/- 0.003 K. The ligand-ligand interactions for both of the complexes were theoretically analyzed. The calculated results agreed well with the experiments. The stronger antiferromagnetic behavior observed in both the complexes at high temperatures was attributed to the magnetic interaction between the Mn(II) and the coordinating nitroxide oxygen atom. The weaker ferromagnetic interaction, J(S=2)/k(B) = +0.31 +/- 0.01 K, in the pyrimidine complex was attributed to the coulombic O6-C2 contact. Antiferromagnetic interaction J(S=2)/k(B) = -0.075 +/- 0.003 K in the pyridine complex was attributed to the O6-C3 contact.     

A family of oxo-chalcogenide molybdenum and tungsten complexes, (n-Bu4N)2[M2O2(mu-Q)2(1,3-dithiole-2-thione-4,5-dithiolate)2] (M = Mo, W; Q = S, Se): new synthetic entries, structure, and gas-phase behavior

A new series of complexes with the general formula (n-Bu4N)2[M2O2(micro-Q)2(dmit)2] (where M = Mo, W; Q = S, Se; dmit = 1,3-dithiole-2-thione-4,5-dithiolate) have been prepared. Fragmentation of the trinuclear cluster (n-Bu4N)2[Mo3(micro3-S)(micro-S2)3(dmit)3] in the presence of triphenylphosphine (PPh3) gives the dinuclear compound (n-Bu4N)2[Mo2O2(micro-S)2(dmit)2] [(n-Bu4N)2[2]], which is formed via oxidation in air from the intermediate (n-Bu4N)2[Mo3(micro3-S)(micro-S)3(dmit)3] [(n-Bu4N)2[1]] complex. Ligand substitution of the molybdenum sulfur bridged [Mo2O2(micro-S)2(dimethylformamide)6]2+ dimer with the sodium salt of the dmit dithiolate also affords the dianionic compound (n-Bu4N)2[2]. The whole series, (n-Bu4N)2[Mo2O2(micro-Se)2(dmit)2] [(n-Bu4N)2[3]], (n-Bu4N)2[W2O2(micro-S)2(dmit)2] [(n-Bu4N)2[4]], (n-Bu4N)2[W2O2(micro-Se)2(dmit)2] [(n-Bu4N)2[5]], and (n-Bu4N)2[Mo2O2(micro-S)2(dmid)2] [(n-Bu4N)2[6]; dmid = 1,3-dithiole-2-one-4,5-dithiolate], has been synthesized by the excision of the polymeric (Mo3Q7Br4)x phases with PPh3 or 1,2-bis(diphenylphosphanyl)ethane in acetonitrile followed by the dithiolene incorporation and further degradation in air. Direct evidence of the presence of the intermediates with the formula [M3Q4(dmit)3]2- (M = Mo, W; Q = S, Se) has been obtained by electrospray ionization mass spectrometry. The crystal structures of (n-Bu4N)2[1], (PPh4)2[Mo2O2(micro-S)2(dmit)2] [(PPh4)2[2]; PPh4 = tetraphenylphosphonium], (n-Bu4N)2[2], (n-Bu4N)2[4], (PPh4)2[W2O2(micro-Se)2(dmit)2] [(PPh4)2[5]], and (n-Bu4N)2[6] have been determined. A detailed study of the gas-phase behavior for compounds (n-Bu4N)2[2-6] shows an identical fragmentation pathway for the whole family that consists of a partial breaking of the two dithiolene ligands followed by the dissociation of the dinuclear cluster.