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J . CHEM. SOC. DALTON TRANS. 1995 3 103Is Hydrazoic Acid (HN,) an Intermediate in the Destructionof Hydrazine by Excess Nitrous Acid?Anne M . M. Doherty,a Kevin R. Howes,b Geoffrey Stedmad and Memdoh 0. Najiba Science Department, Worcester College of Higher Education, Hen wick Grove, Worcester WR2 6AJ, UKChemistry Department, University of Wales Swansea, Singleton Park, Swansea SA2 8PP, UKThe kinetics of the decomposition of NH,N=NOH, the intermediate absorbing at 225 nm formed inthe nitrous acid-hydrazine reaction have been studied by stopped-flow spectrophotometry at aciditiesup to 1 mol dm-3 H+. A substantial amount of protonation occurs at high acidities, and the pK, ofNH,+N=NOH is 0.57. In excess hydrazine decomposition occurs to form hydrazoic acid (HN,), but inexcess nitrous acid a rapid second nitrosation occurs by a diffusion-controlled reaction between NOtand NH,N=NOH which can bypass this pathway, though the possibility of some hydrazoic acidformation cannot be ruled out.Spectrophotometric evidence has been obtained for the formation of arelatively stable species, probably a very minor component, a product of the double-nitrosation reaction.Hydrazine is frequently used as a nitrite scavenger in reactionsystems where it is necessary to remove the last traces of nitrousacid. This is particularly important where the reaction mediumis aqueous nitric acid, because nitric and nitrous acids react toform the nitrogen(1v) oxides N,04 and NO,, which can act aspowerful redox catalysts. Its excellence as a scavenger arisesfrom the fact that the hydrazinium ion reacts with NO' atalmost the encounter rate,' and as it is only weakly basic it isnot significantly deactivated by undergoing a secondprotonation.Rates of nitrite scavenging by hydrazine insolutions up to 15 mol dm-, nitric acid have been measured.,Hydrazine reacts only very slowly with nitric acid, and is thus apotential useful nitrite scavenger in nuclear fuel reprocessing.At acidities above 1 mol dm-3 H', and with excess hydrazine,the product is almost 100% hydrazoic acid, equation (l), thoughN2Hs+ + HNO, - HN, + 2H,O + H + (1)at low acidities ammonia and dinitrogen monoxide are alsoformed. 'At other stages in the reprocessing cycle it may be necessaryto destroy unreacted hydrazine, and this can easily be done byreaction with excess nitrous acid, equation (2).Hydrazoic acidN,H,+ + 2HN0, --+ N, + N 2 0 + 3H,O + H' (2)is known4 t o react rapidly with nitrous acid as shown inequation (3), and hence is a plausible intermediate in reactionHN, + HNO, __+ N, + N,O + H,O (3)(2). However an isotopic tracer study with "N-labelledhydrazine has shown that other reaction pathways also exist.In view of the fact that hydrazoic acid is volatile, explosive andtoxic it is desirable to understand the detailed mechanism ofreaction (2), and to see whether hydrazine can be destroyedwithout generating hydrazoic acid as an intermediate. Previouswork ' on the hydrazine-nitrous acid reaction concentrated onreaction in excess hydrazine, at acidities below pH 1.Thepresent work is concerned with much more acidic solutions,and the effect of excess nitrous acid on the kinetics ofdecomposition.Ex per imen t a1were used without further purification.Materials. -All of the chemicals were Analar materials andKinetics.-Rapid reactions were followed on a CanterburySF 3A-stopped-flow instrument with a data collection system.The disappearance of nitrous acid was followed at 360 nmwhere there is a characteristic, low-intensity absorption. Thegrowth of the intermediate was followed at 253 nm, on the longwavelength side of the absorption maximum; our stopped-flowdid not function well at lower wavelengths due to scatteredlight. Repeated scan spectra were run on a Unicam SP8-200spectrophotometer. Pressure measurements for gas evolutionwere made with a standard pressure transducer calibrated forthe evolution of N, + N 2 0 by reaction (3).Solutions weremade up to constant ionic strength with LiClO,.Results and DiscussionReaction in Excess Hydrazine.-Previous work has shownthat in mildly acidic media, pH 1-3, nitrous acid reacts withexcess hydrazine by a rate determining N-nitrosation, followingrate-law (4), to form a product absorbing at 225 nm, reactions-d[HNO,]/dt = k[H+][HN0,][N2H5+] (4)HNO, + N2H5' 4 NHZNHNO + H2O + H + ( 5 )NH,NHNO 3 NH,N=NOH (6)(5) and (6) respectively. On the basis of spectroscopic andkinetic arguments this was concluded to be trans-NH,N=NOH,formed by the rapid tautomerisation of the initially formedN-nitrosohydrazine. This is analogous to the well establishedmechanism of the diazotisation and deamination reactions.To establish that there is no build up of any precursor toNH,N=NOH we have followed the kinetics of formation ofNH,N=NOH and shown that they follow the same rate law,with the same rate constant as for the disappearance of nitrousacid.Traces showing the growth of NH,N=NOH are shown i3104 J .CHEM. SOC. DALTON TRANS. 19950 200 400tlSFig. 1 Absorbance us. time scans for the hydrazine-nitrous acidreaction at 250 nm: 104[N2H,+] = 9.6; 103[H'] = 4.8;105[HN0,] = 3.2 (a), 6.4 (b), 9.6 (c), 11.2 (d), 20.0 (e) mol dm-3Table 1 Kinetics of formation ( k , ) and decomposition ( k , ) ofNH,N=NOH at 0 "C ([HN0210 = 0.004, [N,H,+], = 0.06, I = 1.0rnol dm-3)[H+]/mol dm-3 lO2k2/s k , , s - ' 4dm3 mol ' cm0.I0.20.40.60.81 .o1.45 2962.24 2633.12 7.4 1533.71 10.8 1234.03 12.1 1084.27 14.0 97Fig. 1, and these also illustrate the fact that the intermediateundergoes a slow, acid-catalysed decomposition, the kinetics ofwhich were previously established at low acidities to followrate law (7) at 25 "C.v = 1.07[H+][NH2N=NOH] rnol dm-, s ' (7)With conventional spectrophotometry it was not practicableto extend these measurements below about pH 2. To study thereactions at acidities closer to those of industrial interest it wasnecessary to go to 1 rnol dm-, H + , where the kinetics were muchfaster. We reduced the rate by working at O O C , and usedstopped-flow spectrophotometry. With our equipment it wasnot practicable to work at 225 nm, and measurements on theformation and decay of the intermediate were made at 253 nm.With a fifteen-fold excess of hydrazine over nitrite the rate offormation of NH,N=NOH was much faster than its decay.Both reactions followed pseudo-first order kinetics with rateconstants k , and k , respectively shown in Table I .Measurements at 363 nm for nitrous acid and 253 nm forNH,N=NOH confirmed that rate law (4) held at higheracidities and that the rate of loss of nitrous acid was still equalto the rate of formation of the intermediate.The spectrum ofthe solution at the end of the reaction was that expected forhydrazoic acid, with a broad maximum at 258 nm.From theintensity of this peak we confirmed that at high [N2H5+I0 theproduct was 98% hydrazoic acid. Its identity was confirmed bymaking the solution alkaline and observing the expected changeto the azide ion spectrum.Acid-Base Properties of the Intermediute.-The kinetics of thedecomposition of the intermediate showed a marked changefrom the low-acidity behaviour. The rate constant k , tended tolevel off at higher acidities, as can be seen from the data in Table1, and the absorption coefficient E of the intermediate decreasedmarkedly as the acidity increased. This suggests that a sizeablefraction of the intermediate is being protonated, giving rise to adecrease in absorbance, and a levelling off in rate becausefurther increases in [H'] do not significantly increase theconcentration of the conjugate acid species.For such a systemthe rate constant k , should vary as shown in equation (8), whereK, is the dissociation constant of the conjugate acid and k , is therate constant for the decomposition.A plot of Ilk, us. l/[H+] yields a good straight line with k, =0.0532 k 0.02 s and K, = 0.268 k 0.013 mol dm '. At lowacidities k , = (k,/K,)[H+]. Combining the present data withthe earlier figure of 1.07 dm3 rnol ' s for k3/Ka at 25 "Cyields an activation energy of 45.6 kJ mol The absorptioncoefficient data were not as good as the rate-constant data, anda plot of l / ~ us. l/[H'] yielded a value of K , = 0.33 rnol dm '.By setting K , = 0.268 rnol dm and assuming that theabsorption coefficient for the conjugate acid is much less thanfor the conjugate base we calculate & 2 5 3 = 460 k 80 dm3mol-' cm-' for NH,N=NOH.The acid-base character of NH,N=NOH was furtherexamined by quenching a reaction solution with [N,H5+] =0.04, [HN0210 = 0.004 and [H'] = 0.026 rnol dm-, in 1 rnoldm-, NaOH 15 s after mixing.This is sufficient time for all ofthe nitrous acid to have been consumed ( t i z 1.1 s) but for verylittle decomposition of NH,N=NOH to have occurred. Thequenched solution showed a new peak at 243 nm, which wasstable for a cu. 1 h. This peak is likely to be due to NH,N=NO-.The compound with the closest structural similarity toNH,N=NOH is trans-hyponitrous acid, HON=NOH, and it isinteresting to compare the two systems.Hyponitrous acid has 'a pK, of 7, so ionisation of NH,N=NOH to NH,N=NO- in1 rnol dm-j sodium hydroxide is reasonable. The wavelengthmaxima for HON=NOH and HON=NO- are 209 and 233 nmwhich compare with 225 and 243 nm for NH,N=NOH andNH,N=NO-. Hyponitrous acid undergoes a slow acid-catalysed decomposition, (9), as observed for NH,N=NOH.HON=NOH --!L N2O + H2O (9)There are differences in behaviour. The anion HON=NO- isnot stable, but decomposes to N,O + OH-. and there is alsoan acid-independent term in the rate law for the decompositionof hyponitrous acid.'Possible sites for protonation in NH2N=NOH are the aminogroup, the hydroxyl group, the double bond and lone pairs onthe double-bonded nitrogens. The reactions of HON=NOHhave been studied up to 11.6 mol dm-, perchloric acid, withno evidence of the formation of measurable amounts of aconjugate acid, so by analogy we exclude the last three sites.General experience would lead one to predict the amino groupas the most basic site anyway.However this does pose aproblem of interpretation of the kinetics, as the obviousdecomposition products of 'NH,N=NOH are NH, + N 2 0 +H + , and ammonia and dinitrogen monoxide are only majorproducts at low acidity.' However, +NH3N=NOH will be inequilibrium with a smaller concentration of the O-protonatedtautomer NH2N=NOH2' and decomposition of this to H' +HN, + H 2 0 seems reasonable with water as a leavinggroup, equation (10). Thus we conclude that the K , value ofNH2N=NOH2++Ht + HN, + H 2 0 (10)0.268 rnol dm refers to the ionisation of the bulk conjugateacid + NH,N=NOH, while the active species in decompositionto hydrazoic acid is a minor tautomer NH,N=NOH, +.At low acidities, where the intermediate exists asNH,N=NOH, the major decomposition products are NH, J.CHEM. SOC.8 0.34e2 0.32C00.300DALTON TRANS. 1995 31051.0usFig. 2 Absorbance us. time traces for the reaction of hydrazine withexcess nitrous acid: [HNO,], = 0.05, [NZH5+], = 0.002, [H'] = 1.0moldmN,O. Both the amide and hydroxide ions are poor leavinggroups, and we are indebted to a referee for the suggestion thathere also the reactive species may be a minor tautomer, in thiscase NH,+N=NO+.Reaction with Excess Nitrous Acid.-This was followedspectrophotometrically at 253 nm by stopped-flow.A typicaltrace is shown in Fig. 2, which shows the formation of theintermediate and its disappearance. The decompositionreaction was very much faster in the presence of excess nitrousacid than it was for reaction in excess hydrazine. Thus in 1 moldm-3 perchloric acid with [HNO,lo = 0.03 and [N,H,+], =0.01 mol dm-, the half-life for the disappearance of theintermediate was 0.48 s, whereas at the same acidity, and withexcess hydrazine it was 16.2 s. Although plots of ln(A - A ,) us.t for the absorbance decay were linear we did not use theapparent pseudo first-order rate constants because there wassignificant overlap between the formation and decay reactions.Thus in the example above, using rate constants for theformation reaction obtained with a large excess of hydrazine,we calculate tt for the formation reaction to be ca.0.14 s whichis not sufficiently small to avoid significant overlap with thedecay reaction. To obtain the order of reaction with respect to[HNO,] we compared instantaneous rates at absorbancescorresponding to a given intermediate concentration, choosingconditions where the formation reaction was essentiallycomplete. This gave an order of 1.06. Variation of the perchloricacid concentration had little effect on the rate of the reactionwith nitrous acid, and the rate law is concluded to be of the form( I 1 ) at acidities close to [H'] = 1 mol drn-,. Values fork, wererate = k,[NH, 'N=NOH][HNO,] (1 1)obtained by computing concentration us.time curves by theGear integration method, using values for k , and k , obtainedby the work with large excess of hydrazine, and trying a rangeof values for k,. We did not have computer optimisationprograms available. The best fit was obtained for k , =200 ? 20 dm3 molWhen reaction rate constants are obtained by such indirectmethods it is important to check that the values are chemicallyreasonable. Nitrosation reactions commonly occur by electro-philic attack by NO+ on the substrate (sub) as shown inequations ( 12) and ( I 3). If the substrate is basic, and is almostscl for 1 mol dm-3 perchloric acid.(12)fast H+ + HNO, ,'NO+ + H,OG oNO+ + sub 3 nitroso product (1 3)fully protonated at the acidities used, then the rate law takesform (14) where K, is the dissociation constant of the conjugateacid, where [sub] represents the total, stoichiometricconcentration of the substrate. Equation (14) yields a value ofkKNo of 946 dm6 mol-' s '.Many nitrosations by NO' takeplace at the encounter rate, with kKNo ca. 2 x lo3 dm6 molP2s-' at 0 "C for anionic nucleophiles.8 The rate constant for aneutral nucleophile will be expected to be a little smaller, so ourrate of 946 dm6 rnol-, SKI is physically reasonable, and weinterpret the nitrous acid catalysed decomposition of theintermediate as involving encounter controlled nitrosation ofthe free base form NH,N=NOH by NO'.With this rate constant we can now compare the rate ofconversion of the intermediate to hydrazoic acid by use ofequation (10) with the rate of destruction by excess nitrous acid.For 1 mol dm-, H+ the rate of azide formation is 0.041 [NH, '-N=NOH], while in the presence of 0.02 mol dm excess nitrousacid the rate of the nitrite path is 4[NH3'N=NOH] about twoorders of magnitude faster.It is clearly possible to destroyhydrazine with excess nitrous acid without generatingsignificant amounts of hydrazoic acid by reaction (10). Therelative rate of destruction by HNO,, vD, and of formation ofhydrazoic acid, vA, vD/vA = 4765 [HNO,]. Unfortunately theconclusion is not as clearcut as would appear. Another way inwhich hydrazoic acid could be formed is by nitrosation ofNH,N=NOH at the hydroxyl group, followed by loss of nitrousacid, reaction (1 5).NO+ + NH,N=NOH - NH,N=N*O(H)NO+ --+H+ + HN, + HNO, (15)However HNO, is not noted as a good leaving group, and theacid-catalysed reactions of alkyl nitrites, RO( H)NO + involvethe loss of NO' with ROH being formed.A closer comparisonis with the reaction of nitrous acid and trans-HON=NOH.There is no sign of an electrophilic nitrosation at oxygen withthe formation of H+, N,O and HNO, [the analogous processto reaction (15)]. Nitrosation at oxygen at an N-OH groupdoes occur in the nitrosation of +NH,OH, but the rate is manyorders of magnitude lower than the encounter rate.' Thus,although reaction (1 5) is a possibility it seems unlikely to be asubstantial contributor to the rate. The isotopic studies of thedistribution of tracer in N,O and N, in the reaction of15N2H5+ with HNO, led to the suggestion that dinitrosationmight occur to yield ON' ,NH1 ,NHNO (which would form15NN0 + and also H15N=NN(NO)OH (which waspostulated to form I5N, and N,O).These are the most likelyproducts of our second nitrosation though we cannot exclude acontribution from a reaction such as (1 5).Evidence for a Further Intermediate Species-During theabove studies it was discovered that the disappearance of the225 nm peak was followed by another, very much slowerprocess in which a small peak at 230 nm decayed. This had beenmissed in the original studies because the reaction was verymuch slower and the absorbance changes were very muchsmaller than the corresponding features of the 225 nm species.Quenching the solution in 1 rnol dm-, sodium hydroxideconfirmed that we were seeing a distinct species, with thedisappearance of the 230 nm peak and the appearance of a newpeak at 273 nm with no sign of a peak at 243 nm.On re-acidification the 230 nm peak reappeared. In a series ofquenching experiments carried out over a range of conditionsthe ratios of the absorbances at 230 and 273 nm were constant,suggesting that the two species were related by acid-baseequilibria.The kinetics of decay of these species were examined bypreparing a stock solution of the 230 nm intermediate in whichdecomposition had been quenched by making the pH 10.1. A3 106I I I I I It3- -2- -1 - -0 I I I I 1 1j. CHEM. SOC.DALTON TRANS. 1995Fig. 3 Variation of k, with pHTable 2pH lo4 k,'/s-' lo4 k,"js pH lo4 k,/s lo4 k,'/s-'Kinetics of decomposition of the minor product at 25 "C1.27 3.22 3.27 4.62 1.22 1.182.83 3.20 3.15 5.11 0.71 0.723.27 3.22 2.97 5.66 0.47 0.503.59 2.95 2.70 5.87 0.46 0.474.03 2.10 2.12 6.37 0.40 0.424.25 1.75 1.75' Experimental. " Calculated from k, = (k,[H+] + k,K,)/(K, +[H']), see text.this acidity the 273 nm peak did not decay to a measurableextent over a time scale of hours. Aliquots of this stock solutionwere added to a large excess of buffer solutions of various pHvalues, and the kinetics of decomposition followed spectro-photometrically. Individual runs gave good first-order plotsof ln(A - A , ) us. t , k,, and Fig. 3 shows the variation withpH.This has the characteristic sigmoid shape for a reactioncontrolled by an acid-base equilibrium, in which both acid andbase species decompose with rate constants k , and k,. The linein Fig. 3 was calculated with k, = 3.27 x 10 s ', k , =4 x s-l and K, = 6.33 x 10Values of k4 calculated from these figures are compared withthe experimentally measured values in Table 2. The spectrum ofthe base species at pH 6.37 showed a peak at 260 nm. At this pHmore than 99% of the intermediate is in the conjugate baseform, and has a slow but measurable rate of decomposition,kobs z 4 x lop5 s-l. When the intermediate is at pH 10.2 thepeak is at 273 nm, and there is no observable decomposition.There must therefore be another acid-base equilibrium with apK, between about 7 and 9, but we have not investigated thispoint any further.While it is clear that there is a new and distinct speciespresent, its identification is more difficult.The relatively slowdecomposition of the 230 nm peak makes it possible to estimatethe relative concentrations formed under different conditionsby measuring the 'initial' absorbance at the wavelength after themuch more rapid decay of the 225 nm peak is complete. Valuesare shown in Table 3. There is a marked increase in initialabsorbance at 230 nm as [N2H,+], decreases. This cannot bedue to parallel reaction between hydrazine and nitrous acid, asthe concentration of a species formed in this way should beindependent of [N2H5+],. At [N2H5+], = 0.4 mol dm thet+ for the disappearance of nitrous acid is about 0.01 7 s, while at0.02 rnol dm-3 it is ca.0.34 s. The longer lifetime of nitrous acidat low hydrazine concentration will favour reaction betweennitrous acid and the intermediate NH,N=NOH. This hasbeen confirmed by a numerical integration of the system ofdifferential equation by the Gear method. Thus even with alarge excess of hydrazine [HN02], = 0.004, [N2H5+], =mol dm-3 (pK, = 4.2).Table 3230 nm at 25 "C ([H'] = 0.5, [HNO,], = 0.004 mol dm-3)Values of the 'initial' absorbance for the species absorbing at[N,H,+],/mol dm A2300.40 0.0970.08 0.3150.02 0.4 140.004 0.683Table 4structures using a 3-21 G basis setAh inirio calculations of formation energies for variousEfiaurruns-NH,NH-NO - 238.450 3540cis-NH,NH-NO -238.454 6179trans-NH,N=NOH - 238.463 075cis-NH,N=NOH - 238.473 2436rrans,rruns-ON-NHNH-NO - 366.336 0rrclns,trans-HON=NNH-NO - 366,340 4cis,cis-HON=NN=NOH - 366.347 0rrans,cis-HN=NN(OH)-NO - 366.324 3I - 366.342 8I1 - 366.334 4The designations cis and trans refer to the geometry of the nitrogenand/or oxygen atoms about the linkages designated by single or doublebonds.Further details of these calculations can be obtained from G.S.;au = Hartree z 4.360 x 10 J.0.06, [H '1 = 1 mol dm the large rate constant for the secondnitrosation leads to approximately 2.5% of the nitrite reacts bypath (2). Such model calculations confirm that there will be amarked increase in the amount of reaction occurring betweenNH,N=NOH and [HNO,] as [N2Hsf], decreases.Weconclude that the species that absorbs at 230 nm results fromthe reaction of hydrazine with two molecules of nitrous acid,and that it contains two acidic protons. The final point to noteis that hydrazine reacts with an excess of nitrous acid accordingto the stoichiometry in reaction (2) very rapidly, with 2 moles ofgas being released very quickly. The slow decomposition of the230 nm species suggests it is only a very minor side-product, noton the pathway that leads to the rapid evolution of N, + N20.It is formed in such small amounts that it does not significantlydisturb the overall stoichiometry, though it can be detectedspectrophotometrically. With a pK, of 4.2 it seems likely tocontain a hydroxyl group, and a possible structure isHO-N=N-N=N-OH.Attempts to isolate it by precipitationas silver(1) or lead(r1) salts were unsuccessful. In anotherexperiment hydrazine was treated with a slightly more thantwo-fold excess of nitrous acid, and the excess nitrous aciddestroyed with ascorbic acid. The solution was then madealkaline and treated with Devarda's alloy in an attempt toreduce any nitrogen containing compound to ammonia, whichcould be distilled off and determined. This gave an amount ofammonia 1.6 k I .6% of the original hydrazine, indicating thatthe intermediate is present in small amounts only.To examine our system by an alternative approach we havecarried out ah initio calculations" on some of the speciespostulated in our discussions using the GAMESS package atthe 3-21G level.The results are summarised in Table 4. Thecisltrans isomerism in some of the listed structures arises fromthe partial double bond character of the >N-NO linkage,leading to restricted rotation. The calculations predict that thetautomerisation product NH,N=NOH is more stable than theinitial nitrosation product NH,NHNO. For the dinitrosatedspecies, and their tautomeric rearrangement products thecalculated order of stability is HON=N-N=NOH > HON=N-NHNO > ONNHNHNO. The isotopic results requires thatthe reaction of *N2H5+ + 2HN0, should involve at least onepathway forming *N2 + N,O, and H*N=*NN(NO)OH wassuggested as a possible intermediate that could lead to thJ.CHEM. SOC. DALTON TRANS. 1995 3107other evidence we suggest that our minor, relatively stableintermediate is HON=N-N=NOH.I IIAcknowledgementsWe are indebted to British Nuclear Fuels Ltd. for financialsupport, and to Dr. D. E. Parry for guidance in the calculations.isotope distribution, by decomposition to *N2 + cis-HON=NOH. The calculations suggest that this is less stable than anyof the three tetranitrogen species mentioned above. We werealso interested in the possible structure of the relatively stablespecies observed as a minor product of reaction, and weconsidered the ring structures I and 11. The ab initio calculationssuggest that these are less stable than the open-chain structureHON=N-N=NOH. One unexpected feature of the calculationswas the prediction at the 3-2 I G level that cis-NH,N=NOH wasmore stable than the trans isomer.The calculations refer togaseous species, with no allowance for solvation energies,and they refer to thermodynamic and not kinetic stability.Calculations using the same basis set for cis- and trans-HON=NOH again predict the cis isomer to be marginally morestable than trans, although there is no doubt6 that the transisomer is more kinetically stable than the cis form. Calculationswith a larger basis set, 4-3 lG, predict trans-NH,N=NOHto be very slightly more stable than the cis structure. Suchcalculations cannot provide conclusive evidence when there aresmall differences in energies for gas-phase structure, whereasthe actual reactions take place in solution, and are governed bykinetic as well as thermodynamic factors. In the absence ofReferences1 J. R. Perrott, G. Stedman and N. Uysal, J. Chem. SOC., Dalton2 K. R. Howes and G. Stedman, J. Chem. Res., 1993, ( S ) 20.3 D. G. Karraker, Inorg. Chem., 1985, 4470; A. D. Kelmers andD. Y. Valentine, Report ORNL/TM6521, Oak Ridge, TN, 1978.4 G. Stedman, J. Chem. SOC., 1959,2943.5 R. J. Gowland, K. R. Howes and G. Stedman, J. Chem. SOC., Dalton6 M. N. Hughes, Q. Rev. Chem. SOC., 1968,22, 1.7 M. N. Hughes, G. Stedman and P. E. Wimbledon, J. Chem. Soc.,8 D. L. H. Williams, in Nitrosation, Cambridge University Press,9 M. N. Hughes and G. Stedman, J. Chem. SOC., 1963,2824.Trans., 1976,2058.Trans., 1992, 797.Dalton Trans., 1989, 533.Cambridge, 1988, p. 10.10 W. J. Hehre, L. Radom, P. v. R. Schleyer and J. A. Pople, Ab-initio11 M. F. Guest and P. Sherwood, GAMESS, an ab-initio program,Molecular Orbital Theory, Wiley, New York, 1986.The Daresbury Laboratory, Warrington, 1992.Received 24th March 1995; Paper 5/0 19 14
ISSN:1477-9226
DOI:10.1039/DT9950003103
出版商:RSC
年代:1995
数据来源: RSC