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A differential scanning calorimetry study of picoline complexes of cadmium chloride
-Act&
19
119423
68 Emficrscicu~m~~gcompany,~
A
De
PICOLINE
-RilltCdillBdghl
SCANkING
COMPLEXES
J- E. HOUSE, JR AND ALLEN L. DV of Chanimy, ffiis Scare _ (Raxmai2AJrmc1976)
CALORIMEIRY
OF CADMIUM
STUDY
OF
CHLORIDE
ROHNER Wm9xrsfly, Normal, ZlL 61761
The decomposition of p&line complexes of cadmium chloride has been studiedusingdiEiEreutial scarmingcalorimetry.The 2~1complexeswith 3-picolineand 4-picoline dccomposc in threesteps correspondingto the loss of one, one-third,and two-thirdsof a moleculeof figan& respectively,in thesesteps_Sample size apparentiy controlsthe mode of decompositionof the I:1 complexwith2-picoline_In so= cases, two-thirdsof a molecule of ligaud is last and in other cases one-thirdis lost first. Thermal parametershave been determinedfor the variousdecompositionreactions. IN’IRODUCIlON
A very large number of complexeshave been studied thermaUyin which the &and donor atom is nitrogen’. However, many of the studieshave been of a rather cursory nature, carried out to determine decomposition temperaturesor relative stabilitiesof a series of complexes_In recent years, modern thermaImethods have yieldeda weaithof therm~yuamic and kineticdata on such systems, Somewhat surprisingly,the xiumbcrof studiescarriedout on cadmium cornplexes is rathersmall. Among the most extensivelystudiedcadmium complexesare the complexes with ammonia, ethyienediamine,and dipyridy12_Also, the thermal decompositionof the pyridinecomplexesof cadmiumhalideshavebeeninvestigated’_ It was reportedthat the decompositionof the pyridinecompkzxesfollows the steps
.The AEZ values reported for these reactionswere 15-6, 3.6, and II-2 kc4 mol-‘, respeztively3_ The work describedherewas carriedout to providereliabledata 011the decompositionof the picolinecomplexesof cadmiumchlorideand to d&-mine their &composition pattems-
120 -AL
The 21 compIexesof 3-picoline(3-pie) and 4picoIine (4-pit) were preparedby treating0.02moIes of finelyground CdC&-2.5Hz0 with 0.2 moIes of the picohne. The mixturewas maintainedat 100°C for 8 h and shakenf_uentIy. After heating, acetonewas added to the mixtureand it was cooled on ice.The soIid compIexeswere washed with cold acetone.After washing,the productswere allowed to dry in air at room temperature.As prepared,the complex with 4-pit yielded 17.17% CI due to someCd@-pic).&& presentas au impurity.To convertthisimpurityto Cd@-pic),CI,, sampleswere thenheatedat 50°C for 2 h. For two separatebatches,the resuhswere as foIIows.Anal: c&d. for Ca(4-pic)&Iz: CI, 19.19%; found, 19.24%and 19.33%. G&d. for Cd@-pic),CI, : CI, 19.19%; found, 19.98%.The 1:I compIexwith Z-pit was preparedas descrimbed above as we11as by dissolvingthe CdcI,-25H,O in hot aIcoho1and adding the 2-pit to the reIIuxingsoIution.The product was treatedas before. Anal.: caIcd. for Cd(2-pic)CI,: CI, 25.65%; found, 25.69%. DSC studies were carried out as previously described* with mass losses determinedby reweighing the sample after each endothermicpeak was passed. Activationenergieswere determinedby the method of Thomas and CIarke using a Ieast squares program to detcrminethe sIopess_Peak areas were determinedby ,=phicaI integration,and enthaIpyvaiueswere caIcuIatcdusingthefusion of metaII.ic .tinasastanda.rd-T’S
AND DISCUSSION
The i”l compIexof 3-pit with cadmiumchIoridewas obtaineddirectly.In the cast of the complex with Z-pit, ouIy the I:1 complex was obtained ahhougb the cadmiumprobably maintainsa coordinationnumber of four by means of chloride bridges.The reasonfor thisdifferencein thecaseof 2-pie may be thesterice&ct when the methylgroup is in the 2-position.There is ample evidenceto indicatethat compIexesof 2-pieare frequentlyeasierto dissociatethanare thecorrespondingcomplexes of 3-pit and 4-pic6.‘With epic, a greater thau 21 ratio of Iigand to metaI was obtained initially. This was due to some Cd@-pic),cI, presentas an impurity.This materialis relatively unstableand isconvertediu 2 h at 50°C to Cd(LLpic)&I,. After heating,the material gave a good sndysis for Cd(4-pic)zCIt,and this materialwas used for aII quantitative DSC runs. When the impure4-pie complexis used in the DSC, an endothermoccurs at sIightIyabove room temperaturecorrespondingto conversionof Cd(4-pic),Q= to Wbpic),cI,DSC curvesobtainedduringthedecompositionofthe 3-pit and 4-pit compIexes showed three endothermicpeaks. IMass loss data were used to es&Wish that the reactionsgiving rise to thesepeaks are
where pit representseither3-pit or 4-pit. The masslossesand thermaldata for these reactionsare given in TabIe I. TABLE
1
THERMAL
DATA
3-pie (1)
381 458 519 391 499 556
3-pit 0) 3-pit (3) 4pic (1)
4-pit (2) 4-Pk G) l
Men
FOR DE~OAMPOSSTION
446 501 584 452 548 600
25.20 11.23 25.30 25.20 11.23 25.30
vaIuesfavaa@deviation
OF Cd(3-pic)&lz
25s8fOS7 11.63&0.80 24.88 f 0.30 23.7oi 1.19 13.49f0.72 23_42fO_61
AND
19.86fO.12 23.1630.20 54.901135 -
Cd(4-pic)zQz*
17.87% 1.02 5.43 f I -27 16.17-L I.11 16.23fO.SO 5.73 f0.12 9.50 zko.29
from the mean. * Additional mass loss for each sxcp.
The data shown in Table 1 indicatethat the loss of one moleculeof lizand from the 3-pit and 4-pit complexesrequiresabout threetimesas much heat as the loss of one-thirdof a &and moleculedoes in the secondstep.Such a resultis expcctcdsince thereis probabIy no differencein the way in which the &and is bonded in the two cases.In the third step of the decompositionin which two-thirdsof a picoiineis lost, AH should be about twice what it is for Step II and about two-thirdsthe value for StepI. Here theagreementis not as good, possiblyowing to moreextensiverearrangement in totally decomposingthe complex. The decompositionof the materialhaving the compositionCd(2-pic)Cl, was found to be similar to the second and third stepsof the decompositionof the 3-pit and 4-pit compkxes. There was one significantdifferencewhich dependedon the sampleweight.cd(2-pic)Cl, was found to decomposein two stepswith two difkrcnt patternsbeing followed. The fhst schemeis W2-pic)Q,,
+
Cd(2-pic),&l~~,i-2/3 2-pictiI
cd(2-pWx13~2~s~ + ~Cbcsl+ 1132-pictij
(4)
0
This patternwas followed for samplesin the range of 2-5 mg. Expcckd additional mass Iossesfor reactions(4) and (!5)are 224.6and 14.48%,respectively. Mass losses found experimentallywere 21.05and 15.64% for thesereactions. When samplesin the 8-10 mg range were used,the decompositionfollowed the l-E%ZiOrrS
122
Cd(2-pic)~,&Ixs,_ +
Ckitias,+2j3%p&,
-:
-..
_.
_. m
For thesere&tions, t.he.expecMmasslossesare 1123 and 2!530%,respccGveIyThe experImcntalmass IoSsesfor deco&osi~ori of thesehuger sampIe+zre II.81 and 24.33%,Thw it is apparentthathuger samplesof cd(&YiC)a~ decomposeaazord.Sg tocqns(~and~,sevcralsamplesbeingusedineachcast.TheeifectofsampIe-~ isprobabljuluetodifE&Wes inthediffasionratesofthegreattramormtoffieeIigand hW Corn larger sampIe~ Less of this l&and w-out of the containerand, thercforc.only one-thirdof a @and is Iost in theinitialstep_Table 2 shows the thermal data for all thesereztions of w2-pic)Ci, _ The data shown in Table 2 revealthat reaction(7) absorbs almostexactlytwiceas much heat as is absorbed in reaction(6)_ Sucharesnltisnd, Expected sincethe amonnt of figand being driven off is twice asgreatinreaction(7). TABLE
2
THERMAL
DATA
FOR
DECOMPOSlTION
OF Cd@pic)CIf
For rea&ons (Q-o-() in the decompositionof cdo,cI,, Beechet ai. reported AHv&es of W-6,3.6, and 11.2kcaI mol-‘, respectively9The slightlyhighervalues obtainedin this work for the 3pic and 4pit compIexe!s would be expectedCorn the faCrthatmethyIpyridines are s&htIy more basic than pyridine-The difExencesin the ability of the vzuionspicoIinesto form z-bonds and the eScts of basicityhave been amPlYreviewedsoand wiiI not be discussedfixrtherhere.Sincethe complexwith 2-pit contains a metal/Egandratio of 19, its decompositionshould be compared with reactions(2) and (3) for the 3-pit and 4-pit complexes.Thus, reactions(6) and (7) representthesamedecompositionpatternof the2-pit complexa$ thatobservedin the last two stepsof the decompositionof the 3pic and 4-pit compIexes.For the complexesof 3pic and 4-pit, the sum of the heats of reactio& (2) and (3) are 2i.6 and 152kcal mol-‘, rqxctivefy- For the 2-pit compIex, the m_ of the heats of reactions(6) and (7) is 148 kcalmol- I_ Thns, the decompositiotiof cd(2-pic)CIz does require less heat than the decompositionof eithercdocI, or Cd@-pic)c1,, althoughnotsigni&zntiysointhelattercase~ -1. . :
123 REFERENCES
3 G~Beech,CT~MorclmerandE,G-Tylcr.J1~soC(A),(196p)S12 4 k Akhaveiu and J. E. House, Jr., L Inorgs MuL CAan, 32 (1970) 1479w S 3. M. Thomas and T. h Clarke, I, Chem Sot (A), (1968) 437. 6G.Beech,CT.MortimicrsadEG.Tyla,I.Chrm.Soe.(A),(I961)1111. 7 O_G_Strodeand3_EHoase.Jr, za?mw&a Acq 3 (1972) 46L 8 G_Rrrdr_CT-Mo~8PdEG.T~~J-CAan-~Q,(1967)~9 s- MmNdson and T- MmShcphact, Inorg, C&m, 4 (l%S) 813-
19
119423
68 Emficrscicu~m~~gcompany,~
A
De
PICOLINE
-RilltCdillBdghl
SCANkING
COMPLEXES
J- E. HOUSE, JR AND ALLEN L. DV of Chanimy, ffiis Scare _ (Raxmai2AJrmc1976)
CALORIMEIRY
OF CADMIUM
STUDY
OF
CHLORIDE
ROHNER Wm9xrsfly, Normal, ZlL 61761
The decomposition of p&line complexes of cadmium chloride has been studiedusingdiEiEreutial scarmingcalorimetry.The 2~1complexeswith 3-picolineand 4-picoline dccomposc in threesteps correspondingto the loss of one, one-third,and two-thirdsof a moleculeof figan& respectively,in thesesteps_Sample size apparentiy controlsthe mode of decompositionof the I:1 complexwith2-picoline_In so= cases, two-thirdsof a molecule of ligaud is last and in other cases one-thirdis lost first. Thermal parametershave been determinedfor the variousdecompositionreactions. IN’IRODUCIlON
A very large number of complexeshave been studied thermaUyin which the &and donor atom is nitrogen’. However, many of the studieshave been of a rather cursory nature, carried out to determine decomposition temperaturesor relative stabilitiesof a series of complexes_In recent years, modern thermaImethods have yieldeda weaithof therm~yuamic and kineticdata on such systems, Somewhat surprisingly,the xiumbcrof studiescarriedout on cadmium cornplexes is rathersmall. Among the most extensivelystudiedcadmium complexesare the complexes with ammonia, ethyienediamine,and dipyridy12_Also, the thermal decompositionof the pyridinecomplexesof cadmiumhalideshavebeeninvestigated’_ It was reportedthat the decompositionof the pyridinecompkzxesfollows the steps
.The AEZ values reported for these reactionswere 15-6, 3.6, and II-2 kc4 mol-‘, respeztively3_ The work describedherewas carriedout to providereliabledata 011the decompositionof the picolinecomplexesof cadmiumchlorideand to d&-mine their &composition pattems-
120 -AL
The 21 compIexesof 3-picoline(3-pie) and 4picoIine (4-pit) were preparedby treating0.02moIes of finelyground CdC&-2.5Hz0 with 0.2 moIes of the picohne. The mixturewas maintainedat 100°C for 8 h and shakenf_uentIy. After heating, acetonewas added to the mixtureand it was cooled on ice.The soIid compIexeswere washed with cold acetone.After washing,the productswere allowed to dry in air at room temperature.As prepared,the complex with 4-pit yielded 17.17% CI due to someCd@-pic).&& presentas au impurity.To convertthisimpurityto Cd@-pic),CI,, sampleswere thenheatedat 50°C for 2 h. For two separatebatches,the resuhswere as foIIows.Anal: c&d. for Ca(4-pic)&Iz: CI, 19.19%; found, 19.24%and 19.33%. G&d. for Cd@-pic),CI, : CI, 19.19%; found, 19.98%.The 1:I compIexwith Z-pit was preparedas descrimbed above as we11as by dissolvingthe CdcI,-25H,O in hot aIcoho1and adding the 2-pit to the reIIuxingsoIution.The product was treatedas before. Anal.: caIcd. for Cd(2-pic)CI,: CI, 25.65%; found, 25.69%. DSC studies were carried out as previously described* with mass losses determinedby reweighing the sample after each endothermicpeak was passed. Activationenergieswere determinedby the method of Thomas and CIarke using a Ieast squares program to detcrminethe sIopess_Peak areas were determinedby ,=phicaI integration,and enthaIpyvaiueswere caIcuIatcdusingthefusion of metaII.ic .tinasastanda.rd-T’S
AND DISCUSSION
The i”l compIexof 3-pit with cadmiumchIoridewas obtaineddirectly.In the cast of the complex with Z-pit, ouIy the I:1 complex was obtained ahhougb the cadmiumprobably maintainsa coordinationnumber of four by means of chloride bridges.The reasonfor thisdifferencein thecaseof 2-pie may be thesterice&ct when the methylgroup is in the 2-position.There is ample evidenceto indicatethat compIexesof 2-pieare frequentlyeasierto dissociatethanare thecorrespondingcomplexes of 3-pit and 4-pic6.‘With epic, a greater thau 21 ratio of Iigand to metaI was obtained initially. This was due to some Cd@-pic),cI, presentas an impurity.This materialis relatively unstableand isconvertediu 2 h at 50°C to Cd(LLpic)&I,. After heating,the material gave a good sndysis for Cd(4-pic)zCIt,and this materialwas used for aII quantitative DSC runs. When the impure4-pie complexis used in the DSC, an endothermoccurs at sIightIyabove room temperaturecorrespondingto conversionof Cd(4-pic),Q= to Wbpic),cI,DSC curvesobtainedduringthedecompositionofthe 3-pit and 4-pit compIexes showed three endothermicpeaks. IMass loss data were used to es&Wish that the reactionsgiving rise to thesepeaks are
where pit representseither3-pit or 4-pit. The masslossesand thermaldata for these reactionsare given in TabIe I. TABLE
1
THERMAL
DATA
3-pie (1)
381 458 519 391 499 556
3-pit 0) 3-pit (3) 4pic (1)
4-pit (2) 4-Pk G) l
Men
FOR DE~OAMPOSSTION
446 501 584 452 548 600
25.20 11.23 25.30 25.20 11.23 25.30
vaIuesfavaa@deviation
OF Cd(3-pic)&lz
25s8fOS7 11.63&0.80 24.88 f 0.30 23.7oi 1.19 13.49f0.72 23_42fO_61
AND
19.86fO.12 23.1630.20 54.901135 -
Cd(4-pic)zQz*
17.87% 1.02 5.43 f I -27 16.17-L I.11 16.23fO.SO 5.73 f0.12 9.50 zko.29
from the mean. * Additional mass loss for each sxcp.
The data shown in Table 1 indicatethat the loss of one moleculeof lizand from the 3-pit and 4-pit complexesrequiresabout threetimesas much heat as the loss of one-thirdof a &and moleculedoes in the secondstep.Such a resultis expcctcdsince thereis probabIy no differencein the way in which the &and is bonded in the two cases.In the third step of the decompositionin which two-thirdsof a picoiineis lost, AH should be about twice what it is for Step II and about two-thirdsthe value for StepI. Here theagreementis not as good, possiblyowing to moreextensiverearrangement in totally decomposingthe complex. The decompositionof the materialhaving the compositionCd(2-pic)Cl, was found to be similar to the second and third stepsof the decompositionof the 3-pit and 4-pit compkxes. There was one significantdifferencewhich dependedon the sampleweight.cd(2-pic)Cl, was found to decomposein two stepswith two difkrcnt patternsbeing followed. The fhst schemeis W2-pic)Q,,
+
Cd(2-pic),&l~~,i-2/3 2-pictiI
cd(2-pWx13~2~s~ + ~Cbcsl+ 1132-pictij
(4)
0
This patternwas followed for samplesin the range of 2-5 mg. Expcckd additional mass Iossesfor reactions(4) and (!5)are 224.6and 14.48%,respectively. Mass losses found experimentallywere 21.05and 15.64% for thesereactions. When samplesin the 8-10 mg range were used,the decompositionfollowed the l-E%ZiOrrS
122
Cd(2-pic)~,&Ixs,_ +
Ckitias,+2j3%p&,
-:
-..
_.
_. m
For thesere&tions, t.he.expecMmasslossesare 1123 and 2!530%,respccGveIyThe experImcntalmass IoSsesfor deco&osi~ori of thesehuger sampIe+zre II.81 and 24.33%,Thw it is apparentthathuger samplesof cd(&YiC)a~ decomposeaazord.Sg tocqns(~and~,sevcralsamplesbeingusedineachcast.TheeifectofsampIe-~ isprobabljuluetodifE&Wes inthediffasionratesofthegreattramormtoffieeIigand hW Corn larger sampIe~ Less of this l&and w-out of the containerand, thercforc.only one-thirdof a @and is Iost in theinitialstep_Table 2 shows the thermal data for all thesereztions of w2-pic)Ci, _ The data shown in Table 2 revealthat reaction(7) absorbs almostexactlytwiceas much heat as is absorbed in reaction(6)_ Sucharesnltisnd, Expected sincethe amonnt of figand being driven off is twice asgreatinreaction(7). TABLE
2
THERMAL
DATA
FOR
DECOMPOSlTION
OF Cd@pic)CIf
For rea&ons (Q-o-() in the decompositionof cdo,cI,, Beechet ai. reported AHv&es of W-6,3.6, and 11.2kcaI mol-‘, respectively9The slightlyhighervalues obtainedin this work for the 3pic and 4pit compIexe!s would be expectedCorn the faCrthatmethyIpyridines are s&htIy more basic than pyridine-The difExencesin the ability of the vzuionspicoIinesto form z-bonds and the eScts of basicityhave been amPlYreviewedsoand wiiI not be discussedfixrtherhere.Sincethe complexwith 2-pit contains a metal/Egandratio of 19, its decompositionshould be compared with reactions(2) and (3) for the 3-pit and 4-pit complexes.Thus, reactions(6) and (7) representthesamedecompositionpatternof the2-pit complexa$ thatobservedin the last two stepsof the decompositionof the 3pic and 4-pit compIexes.For the complexesof 3pic and 4-pit, the sum of the heats of reactio& (2) and (3) are 2i.6 and 152kcal mol-‘, rqxctivefy- For the 2-pit compIex, the m_ of the heats of reactions(6) and (7) is 148 kcalmol- I_ Thns, the decompositiotiof cd(2-pic)CIz does require less heat than the decompositionof eithercdocI, or Cd@-pic)c1,, althoughnotsigni&zntiysointhelattercase~ -1. . :
123 REFERENCES
3 G~Beech,CT~MorclmerandE,G-Tylcr.J1~soC(A),(196p)S12 4 k Akhaveiu and J. E. House, Jr., L Inorgs MuL CAan, 32 (1970) 1479w S 3. M. Thomas and T. h Clarke, I, Chem Sot (A), (1968) 437. 6G.Beech,CT.MortimicrsadEG.Tyla,I.Chrm.Soe.(A),(I961)1111. 7 O_G_Strodeand3_EHoase.Jr, za?mw&a Acq 3 (1972) 46L 8 G_Rrrdr_CT-Mo~8PdEG.T~~J-CAan-~Q,(1967)~9 s- MmNdson and T- MmShcphact, Inorg, C&m, 4 (l%S) 813-