The thermal properties of some metal pyridinecarboxylates

Amdyli~a Chimica Ada Elscvicr Publishing Company. Prlntcd in The Ncthcrlands

79

Amsterdam

THE THERMAL PROPERTIES PYRIDINECARBOXYLATES

OF

SOME

METAL

G. I>‘hSCEN%O+ AND W. 1%‘.WENDLANDT Depnrlwtcnl

(Ihxcivctl

of Clwntistry.

Nowmbcr

U*riversify

of Houston,

Tile z-, 3-, and S-p?fridit~ccarbosylic

2-pyridinecarboxylic acid (picolinic acid)

Horrsto~i,

Texus

77004

(U.S..4

.)

Ioth. rgGg)

acids,

3-pyridinecarbosylic acid (nicotinic acid)

+pyridinecarboxylic acid (isonicotinic acid)

readily form metal complexes with divalent transition metal ions in solution. These compounds have been isolated, and in the case of z-pyriclinecarboxylic acid (picolinic acid) complexes, have been studied by thermogravimetric analysis (TGA) and diffcrential thermal analysis (DTA) techniques 1- 5. Althou& most of the work has been concerned wit11 picolinic acid, one study” has reported tile thermal stability of the complexes of 3-pyridinecarboxylic acid (nicotinic acid) and 4-pyridinecarboxylic acid (isonicotinic acid) as well. There are a number of discrepancies concerning the thermal properties of the metal complexes of these three acids in the literature, especially with the results iron( cobalt(II), obtainedby KANEI)A AND HARA 0. Accordingly, the manganese(II), nickel( II), copper( II), and zinc( II) complexes of 2-, 3-. and 4-pyridinecarboxylic acids were prepared and their thermal properties determined by TGA, DTA, differential scanning calorimetry (DSQ and !ligh temperature (HTRS) and dynamic reflectance spectroscopy (DRS). EXPERIMENTAL

Instrunients en@!oyed The TGA curves were obtained by use of a DuPont Model g5o thermobalance with dynamic air or nitrogen furnace atmospheres. The sample sizes were 10-12 mg; a furnace heating rate of 10~ per min was employed. A Du Pont Model gzo Thermograph was used to obtain the DTA curves. The samples were studied in both dynamic air and nitrogen furnace atmospheI;es at a heating rate of xo” per min. Sample sizes were S-10 mg. The Yerkin-Elmer Model DSC-rB differential scanning calorimeter whs used * Parmancnt address: Chemical Institute, University of Rome, Romo, Italy. Awd.

Clbiwa. Aclu,

50 (1970)

79-91

G.

Altal.

Ctbitrk. flcln,

50 (1970)

79-91

II’ACSENZO,

W.

W.

WENDLANDT

THERMAL

PROPERTIES

OF

METAL PYRIDINECARROXYLATES

SI

to obtain the calorimetric data. A dynamic nitrogen furnace atmosphere was employed at a heating rate of 10’ per min. Sample sizes were ~-IO mg. Duplicate, and in many cases, triplicate, runs were made on each sample. The curve peaks were integrated by a planimeter technique. The calibration standard was high-purity indium metal, 6.75 cal per g. The reflectance studies were carried out with the heated sample holder previously described by WENIILANDT~-D and a Beckman Model DK-ZA spectroreflectometer. White glass-fiber cloth covered with a thin cover glass was used as the reflectance standard. A heating rate of xo” per min was employed for the DRS mode. Prej5aration

of comj5ounds

acids (Eastman Organic Chemicals, The z-, 3-, and 4-pyridinecarbosylic Rochester, N. Y.) were used without further purification. The other chemicals employed were all of reagent-grade quality. The general procedure for the preparation of the complexes consisted of adding a I iJf solution of the divalent metal chloride to a I M solution of the acid, maintained at a pH of 4, until an acid:metal concentration of 3: I was attained. The resulting mixture was heated to boiling and mechanically stirred for about I 11. The metal complex precipitate, if present, was filtered off, washed with a I :I waterethanol mixture, and then with 95% ethanol and dried igz vacua for 4s h at room temperature. If precipitation from the solution was not spontaneous, 1)51& etlianol was added until a precipitate was obtained. The complexes were analyzed for water and metal contents by TGA. RESULTS

Owing to the large number of TGA, DTA, and rcflcctance curves obtained, only representative curves are shown in Figs. r-5. The thermal decomposition data are summarized in Tables I-III. Each compound will be discussed briefly. The temperatures referred to are the procedural decomposition temperatures at the heating rate indicated. Manganese(II) 2-9yridinecarboxylate This compound is precipitated as the anhydrous complex, Mn(zPC)e. It dissociates in three steps to give the oxide, MnaOs, beginning at 550” (found 25.5O/& theor. z5.4go/o). Constant weight could not be obtained for the metal oxide in a nitrogen atmosphere. The DTA curve contained two endothermic peaks, the latter of whicll was not very well defined. The HTRS (high temperature reflectance spectroscopy) curve had a reElectance maximum of 500 nm which shifted to a higher wavelength as the compound was heated to zoo”. With DRS, the curve obtained at 500 nm began to decrease slowly when heated with a rather large decrease indicated between 180~ and 2~5~. Manganese(II)

3-$yridinecarboxylate

Unlike the 2-pyridinecarbosylate complex, this compound precipitates as the dihydrate, Mn(3PC)z - 2HzO. The water of hydration is evolved by a one-step process (10.7% found, 10.75% theor.) while the anhydrous Mn(3PC)z is stable up to 330” A?znl. Claim. Ada,

50 (1970) 79-91

G. D’ASCIZNZO,

sz TAULE

W.

W.

WENDLANDT

II

PROCl3DURAL

DECOhfPOSlTION

TEMPERATURES

FROM

*%A

DTA

AND

CURVES

Of’

METAL

3-PYRIDINE-

ChRUOXYL,\TES

Air Mn(II)

NZ Air

ik(t

425 330-445

150 X35-180

140 130-160 Go

132 80-165

35-80

r)

415 3‘12-*,+75

N.L Air Co(II)

1‘15 105-l

Ni(II)

x.12 75-165

%II( [I)

4

I0

380-455

BOO--.tzo

‘45 80-I 50

420 380-455

402

102

70-130

288 275-290

415 380-440

G5

4 15 290-475

N3 Air

[25-I40

‘35 r30-155

35-70

Cll(I1)

130

I IO--l25

385-430

NZ Air

II2

412

75

Nz Air

440 405-475

65 55-75

‘05 Y5-120

275 270-250

80

100 95-x=5

425 325-440

115 75-130

Na

70-85

where it undergoes almost explosive decomposition to give the metal oxide, MnsOd (23.3% found, 22.75O/” theor.). The DTA curve has an endothermic peak for the dehydration reaction and a smaller endothermic peak for the decomposition of the complex. The HTRS curve has a maximum at 425 nm with a shoulder peak at 400 nm. This maximum shifts slowly to higher wavelengths as the compound is heated. A pronounced change in the DRS curve takes place above 150~; however, the curve continued to decrease gradually all the way to 250’. Manganese(I1) 4-~yri~~necarboxylate This compound precipitates from solution as the tetrahydrate, Mn(4PC)a *4HaO. According to the TGA curve, the water of hydration is evolved by a one-step process (xg.z% found, lg.41 O/,theor.). The anhydrous complex decomposes very rapidly to give the oxide, Mn304 (2x.1 o/o found, 20.54O/~theor.). The DTA curve shows the one-step dehydration reaction as a single endothermic peak followed by another endothermic peak for the decomposition of the anhydrous compound. Only a shoulder Anal. Chh.

Ada,

50 (1970) 79-91

.

THERMAL TABLE

PROPERTIES

OF

METAL

PYRIDINECARBOSYLATES

83

1II

PROCEDURAL

DECO.ZlPOSITfON

TE.MPERhTURES

FROM

‘l-GA

DTA

AND

CURVES

OF

METAL

4-PYRIDINE-

CARBOXYLATES

Metal

TGA

DTA Hz0

N30 I Air

II

r

Decomp

II

NZ Air

125 105-140

3’0 270-3:Cl

Fc(TL)

4 ‘0 305-4

IO0

85-I Co(II)

15

135 J x5-155

Cu(II)

Zn(II)

Peak II

420

395-440

130 95-140

310 290-330

425 380-445

20

170 x50--180

420 3Go-450

308 275-380

160

140 135 So-rG5

280

250-290

JJ3 85-J 35

I zo-zoo

330 310-335

375 335-420

130

270

280

J25-150

265-z

J”5 90-J 30

440 390-470

330 ac)o-3Go

Na Air

Peak I

110-130

75-r

NZ Air

rl

120

IV0

x20-200

Ni(II)

nzo

390 350-4’5

Na Air

I

*5

Na Air

Hz0

405 325-418

I20

93-150

Mn(I1)

Deco@

75

2 75-295

443 330-463

N3

peak at 4x0 nm is indicated in the HTRS curve and this moves to a higher wavelength as the compound is heated to 250~. This change is shown more dramatically in the DRS curve where the reflectance of the compound decreases sharply above 125~. A more gradual change in reflectance then takes place up to 250~. Iron

2-fiyridinecarboxylate

According to the TGA curve, Fe(2PC)z - 4HzO loses its water of hydration in one step (19.3% found, 19.36% theor.) followed by decomposition of the anhydrous complex to give the oxide, Fez03 (21.9% found, 21.46% theor.). The DTA curve contained a single endothermic peak for the dehydration reaction ; however, the peak contained two shoulders indicating that the reaction may consist of two steps but they were not very well resolved. A shift in the HTRS curve maximum took place from 670 to 725 nm in the temperature range 125-175~. Iron

3-$yridinecarboxylate

This compound

precipitates

frorn solution

as Fe(3PC)z

- 3.5H20.

AIral. Chim. Ada,

The water is 50 (1970) 79-1

34

G. D’ASCENZO,

W.

W.

WEXDLANDT

lost in two steps, the first of which involves 0.5 mole of water followed by the other 3 moles per mole of complex (for 0.5 mole HzO: 2.6% found, 2.48% theor.; for 3 moles HzO: 17.3% found, 17.36% theor.). This was followed by the decomposition of anhydrous Fe(3PC)e to give the oxide, Fez03 (ZZ.I o/ofound, z~.gg~/, theor.). The DTA curve also shows that the water is evolved in two steps. The behavior of the HTRS ::.;: curves was similar to that of Fe(2PC)s - 4H2O. Iron

4-j3yridiltccarboxylate This compound precipitates as Iie(41’C)2 - 2.5H20, the water of which is evolved in a single step (12.9’yo found, 13.0g’yo theor.). The anhydrous compound, l?e(ql?C)z, explodes on heating at practically every heating rate down to 2.5” per min, &vine; the oxide as the residue. The DTA curve gives endothermic peaks for the dehydration and decomposition reactions. The reflectance behavior was similar to that found for l?e(zPC)2 -4H20. Cobnlt(II) 2-~yvidimcarboxylate Tlre tetrahydrate, Co(2l’C)~ -4&O, dehydrates in two steps. The first two moles of water arc evolved over the range 70-115~ while the remaining two are evolved up to 150~. This is in good agreement with the work of TnonlAsh who reported 75-150” while LUMME~ gave the dehydration range as 80-217~. The water evolved was 9.7 and Ig.I”/o found (g-Go and xg.20°/, theor.) for the loss of two and four moles of water, respectively. The anhydrous complex was stable up to 325” where it began to decompose to the oxide, CosOri (21.7% found, 2r.3gyo thcor.). The DTA curve showed two endothermic peaks for the dehydration reaction followed by another endothermic peak causecl by the decomposition reaction. The HTRS curve containecl two peak maxima at 400 nm and 625 nm, respectively. The latter maximum shifted to 675 nm between ‘100’ and 125~ and to Ggo nm above 125”. Two rather indistinct reflectance decreases were observecl in the DRS curve between 75” and 135”. Cobalt(I1) 3-;hyvkEi?lecnrboxyla2e Like the 2-pyridinccarboxylate complex, four moles of water were found for this compound, Co(3PC)z - 4H20. However, the TGA curve indicated tllat all four moles of water are evolved in a single step (x9.8”/, found, Ig.20°/” theor.). The residue of the decomposition reaction is Co304 (21.2% found, 21.39% theor.). The DTA curve indicated only a single endothermic peak for the clehydration reaction and another such peak for the decomposition reaction. Cobalt(II) 4-~yridi~bccarbonylate The complex precipitates from solution as the pentahydrate, Co(4PC)n * 5HzO. Two moles of water are evolved in the first step (9.4”/ found, 9.16% theor.) while the remaining three moles are evolved in the second step (23.g0A, found, 22.90:/o theor.). Anhydrous Co(4PC)z decomposes in one step giving Co304 as the residue (20.2”/ found, 20.41 o/o theor.). The DTA curve contained two endothermic peaks for the dehydration reaction and a single endothermic peak for the decomposition reaction. Nickel (II) z+fiyridinecarbo.xylate This compound precipitates A91nZ. Cl&a. /f&a, 50 (1970) 79-91

from solution as the tetrahydrate,

Ni(2PC)z

- 4HzO.

THERMAL

PROPERTIES

OF METAL PYRIDINECARBOXYLATES

55

The water of hydration is evolved in two steps (Fig. I), each involving two moles of water (9.6% found, 9.61% theor. for the first two moles of water, and xg.3o/o found, 19.22% theor. for the loss of four moles of water). Anhydrous Ni(2PC)z dissociates to the oxide, NiO, in a single step (20.1 y. found, 19.92 o/otheor.). Two endothermic peaks are present in the DTA curve (Fig. 2) corresponding to the loss of the four moles of water. The third endothermic peak is due to the decompo&ition of the anhydrous complex.

Fig. I. Mnss-loss curves of nickcl(1 I) pyridinccarboxylatcs; air ntmosphcrc; 10’ per min; IO-lng z-pyridincc~lrl,oxyl:ttc sample. (A) Nickcl(II) ~-pyri’liIlccnrl,oxyl;rtc 4-hydrzrtc, (U) nickcl(II) q-hpclratc, (C) nickcl(1 I) 3-l~yritlirlcc~rrboxyl~lt~ ,+-hytlratc.

I

I loo

I

I TEMR6%

Fig. 2. L>TA curve of nickcl(II)

I

I

300

I

z-pyriclinccarboxylatc;

NJ atmosphcrc;

IO” per mill ; ro-tng sample.

Nic/rel(II) p$yvidivaecarboxylate As in the case of the 2_pyridinecarboxylate, this compound precipitates as the tetrahydrate, Ni(3PC)z . L+HzO. All four moles of water evolved in a single step on the TGA (Fig. I curve, (B)) (19.0% found, 19.22~/~ theor.). The anhydrous complex decomposes in a single step to give the oxide, NiO (20.1% found, 19.92% theor.). The DTA curve contains two endothermic peaks; one for the dehydration reaction, the other for the decomposition of the anhydrous compound. Anal. Chim. Ada.

50 (1970) 79-91

8C

G. D’ASCENZO,

W. W. WENDLANDT

Niclzcl(II) +$yridinecavboxylate Like the 3-pyridinecarboxylate complex, the tetrahydrate, Ni(4PC)z -4HzO. loses its water of hydration in a single step (19.1% found, rg.zz% theor.) (Fig. I) Decomposition of the anhydrous complex, Ni(qPC)z, is quite rapid to give the oxide, NiO (zo.o~/~ found, 19.92% theor.). The DTA curve contained three endothermic peaks, one for the dehydration reaction, the other two for the decomposition reaction.

60

I

I

I

400

I

I

I

500

I

600

I 700

3fnm)

Pig. 3, High tcmpcrnturo

reflcctancc

curvcs of nickcl( I I) ,~-pyridinccarboxylatc.

lO%R

I 50

I

I 100

I TF*‘P.

Fig. 4. DRS Anal.

I 150

50

(1970)

I 200

I

f-2)

curve of nickcl(I1)

Claim. Acta,

I

79-91

q-pyridinccarboxylatc;

xo” per min;

G50 nm.

THERMAL

PROPERTIES

OF

METAL

PYRIDINECARBOSYLATES

57

The HTRS curve (Fig. 3) has a single reflectance maximum at 425 nm which shifts to a higher wavelength as the temperature increases. At x70”, the peak maximum is 515 nm. The DRS curve (Fig. 4) indicates a one-step reaction, beginning at about 75”. Co~~cr(ZI) 2-j5yridinecarboxylate This compound, which is precipitated as the monohydrate, CU(ZPC)~ - HoO, loses the water in a single step (5.6% found, 5.53% theor.) to give the anhydrous compound, Cu(zPC)2. The latter dissociates almost explosively at 255” to give the oxide, CuO (24.1% found, 24.42% theor.). The DTA curve, as expected, contained only two endothermic peaks, one for the dehydration, the other for the decomposition reaction. The HTRS curves of this compound at various temperatures are shown in Fig. 5. One rather sharp reflectance maximum, at 430 nm, is present in all of the curves. The maximum decreases with increasing temperature and according to the DRS curve, increases to the original reflectance value on cooling. Thus, the Cu(21K)~ .Hz0 complex exhibits thermochromic behavior. The other copper( II) compounds are also therrnochromic, the only metal ion to exhibit this behavior.

lot--W-l_ 400

Fig.

'O"

>(nm)

5. High tempernturc

Copper

600

700

rcflcctancu curves and DRS curves of coppa-

z-pyridinccarboxylato.

3-pyvidiltecavboxylate

Like the preceding complex, the monohydrate, Cu(3PC)z - HzO, is precipitated from solution. This hydrate-bound water is evolved in two steps in the TGA curve; the first step corresponds to a loss of 2.S”A and the second to a total mass-loss of 5.5%. The theoretical values are 2.76% for the loss of 0.5 mole of water and 5.53% for the evolution of one mole of water. The anhydrous complex, Cu(3PC)2, decomposes at a A?aal. Claim. Ada,

50 (1970) 79-91

D’ASCENZO, W. W.

G.

88

WENDLANDT

very rapid rate to give the oxide, CuO (24.7(j% found, 24.42% theor.). The DTA curve confirms the above reactions in that there are two endothermic peaks for the loss of water and a single very narrow peak for the decomposition reaction. _ Co$fwr(II) 4-~yricli?lecarboxyZate Unlike the above complexes, the tetrahydratc is precipitated from solution as Cu(4l?C)~ .4HzO. All four moles of water are evolved in one step (x8.60/, found, lg.01 o/0 theor.), giving the anhydrous compound, Cu(4PC)z, which dissociates in two steps to give the oxide, CuO (20.8~/~ found, 20.gg0/o theor.). The DTA curve contained one endothermic peak for the dehydration and two for the decomposition reaction. %iw(II)

2-$yvidinecarboxylate The tetrshydrate, Zn(2PC)z * 4H20, dehydrates in a single step (r8.80/, found, 18.88~/~theor.) to give the anhydrous compound, Zn(2PC)c. The latter decomposes in found, 21.32 y. thcor.). The DTA curve two steps to give the oxide, %nO (21.50/~ contained one endothermic peak for the dehydration reaction and two not very well resolved peaks for the decomposition reaction.

%im(II)

3-~3lYiclilcecarbo.~ate Unlike the above complex, this compound precipitates from solution as the trihydrate, %11(3lX)~ - 3HzO. The three moles of water are evolved in a single step (15.8~/~ found, x4.8G0/, theor.) giving the anhydrous compound, Zn(3PC)z. The

I-IlmTS olr I~I~IIYDKATION

M&al

co nrp1es

OF

MlS'TAI. I'YIIII~INISCAHI~O.YYLhTlr,S

Dclbydrwtiorr rcactior8 --

a-Pyri(~iltcrcnvbosylntes Pc( [I) ‘+ -> 0 Co(LS) Ni(Ct)

4 --z 0 4 --t 2

Cu(1I)

2 ->o I --to

%n(II)

4 -> 0

Toup. VtlJZbE (“) -------

A,_[

85-140 OX--r 40

32,000 53,000

Or--rr,t 1.to-IS8

23,000

7 l-88 Gr-127

----

(callmole)

27,000 .t.c,oo 50,000

& 950 =t: 1000 =t 700 * So0 * 150 & 1500

3-I~yridi,tncrcrbo.~yl~~tcs Mn(II) Pc(lT)

Co(I1) Ni(l 1) Cu( II)

2+0

3.5 3 ‘1 ‘I 1 0.5

Zn(LI)

+3 -*o ->o 30 -*0.5 -ho

700 zltr 15 27,500 & 800 53,000 & 1000 ‘Q3,OOO & I.150 3,800 * IO0 (3,500 _I 200 50,000 * I500

128-162

23,000

St?-89

5,roo

95--r 40 111-fG7 103-171 59-70 82-122

3+0

63-96

‘t --to

Q-I 35 8X-144

&

4-Pyridilrecai,Oosylntcs iSIn

Fe(II) Co(H)

Ni(fI) Cu(l1) Zn(I1)

Anal.

2.5 30 5 -> 0 4+0 1) -ho

440

Chiwr. Acta,

50 (1~~70) 79-31

GG-I 49 123-177 103-149

54,000 23,000 71,000 54,000 47,000

f f * f zt

&t-112

28,000

f

IGOO

700 200 IGO

1400 so0

THERMAL

PROPERTIES

OF METAL

DYRIDINECARBOSYLhTES

89

anhydrous complex dissociates in a single step, giving the oxide, ZnO (zz.~~/~ found, zz -38 o/otheor.), There are two endothermic peaks present in the DTA curve caused by the dehydration reaction and a single endothermic peak caused by the decomposition reaction. Zinc(II)

++yridinecarboxylate This compound precipitates from solution as the tetrahydrate, Zn(4PC)a -qH20. All of the water of hydration is evolved in a single step in the TGA curve (18.9O/~ found, IS.SS~/~ theor.), giving the anhydrous complex, %(41X)2. The latter dissociates in a single step to give the oxide, %nO (21 .I T/i,found, 21.32 o/0theor.). The DTA curve contains one endothermic peak from the dehydration reaction and another endothermic peak from the decomposition reaction. Heats

of dehydration The heats of dehydration of the metal complexes arc given in Table IV. For the tetrahydrates, the AH values ranged from 2800 f So to 54oof IGO cal per mole with the majority of the values in the 4000-5000 cal per mole range. In general, the ligand has little effect on the dehydration reaction although there are some exceptions to this rule. The AH values were lowest for the monohydrate in terms of cal per mole of water evolved. DISCUSSIOS

The tllcrmal stability of tllc metal complexes is dependent on both the metal ion and the ligand. For the 2- and 3-pyridinecarboxylates, the order of decreasing stability was : Mn > %n = Fe > CO > Ni > Cu; the order was similar for the q-pyridinecarboxylates With zinc,

except

changing

ligand,

that

the zinc

the order

2-pyridinecarboxylates

complex

of decreasing

was

more

stability

> 3-pyridinecarboxylates

stable

than

that

for manganese.

for all of the metal

ions,

> 4-pyridinecarboxylates.

except In

case of zinc, the 4- is more stable than the 3-pyridinecarboxylate. The higher thermal stability of the 2-pyridinecarboxylates is probably due to the ability of this ligand to form chclate bonds through the pyridine nitrogen and carboxylic oxygen to give two five-membered rings. The 3- and 4-pyridinecarboxylates cannot form such a chelatc ring owing to steric factors caused by the position of the carboxyl group. Hence, their metal chelates possess a lower thermal stability. With regard to the mechanism of the thermal dissociation processes of these compounds, it is interesting to note that KANEDA AND HnIrna found cxothermic peaks in the nitrogen atmosphere DTA curves for the cobalt(U), nickel(II), and zinc(I1) z-pyridinecarboxylates and nickel(I1) 3-pyridinecarboxylates. The results of this investigation do not confirm these observations. In a nitrogen atmosphere, only endothermic peaks were found in the DTA curves. However, in an air atmosphere, there was occasionally a violent, exothermic decomposition reaction. The DTA curves in air usually contained an endothermic followed by an exothermic peak for the decomposition reaction. The first stage of the dissociation is therefore endothermic followed by the exothermic oxidation of the reaction products (or intermediates). According to KANEDA AND HARA 6, the first Step in the decomposition of the anhydrous the

compounds

is the release

of the free-radical, AVUL~.Clbint. A&u, 50 (x970)

79-91

G. D’ASCENZO, W. W. WENDLANDT

90

for 3-

for 4 - pyridinecarboxylates

and one mole of carbon dioxide. These radicals then form pyridine and/or bipyridyls. In general, the results described here agree with those previously reportede-G for the degree of hydration of the compounds. There were, however, a number of differences between t!;is work and that of KANEDA AND HARA~, especially for the manganese, cobalt, and nickel 3-pyridinecarboxylates. The thermal, as well as the magnetic susceptibility and infrared data3~4~10~11,support an octahedral structure for the iron( cobalt(I1) and nickel(H) 2-pyridinecarboxylates, while those for copper(I1) and zinc(I1) have a tra?zs-planar configuration. For manganese(I1) 2pyridinecarboxylate, PAHIS AND THOMAS-3 found that the dihydrate was octahedral while the anhydrous compound had the Ivagzs-planar configuration. The data available on the 3- and +pyridinecarboxylates does not permit any conclusions concerning this situation. The financial aid of the U.S. Air Force, Air Force Office of Scientific Research, through Grant No. Al;-AFOSR 69-1620, is gratefully acknowledged. Financial assistance to G.D.A. by the National Research Council of Italy, Rome, Italy, is also acknowledged. SUMMARY

The thermal properties of the divalent metal complexes of z-, 3-, and 4yyridinecarboxylic acids were determined by TGA, DTA, DSC, high temperature reflectance spectroscopy, and dynamic reflectance spectroscopy. The complexes generally precipitate from solution as the hydrate containing r-5 moles of water per mole of complex. The decomposition sequence is first the loss of hydrate water followed by the total disruption of the anhydrous complex to yield the metal oxide as the residue. Each dissociation reaction is discussed in terms of the above thermoanalytical techniques. R@SUMIk

On a determine les proprietds thermiques de complexes de mdtaux divalents des acides 2-, 3- et 4-pyridinecarboxyliques par diverses methodes spectroscopiques. Les complexes precipitent genCralement sous forme d’hydrates, renfermant I h 5 mol8cules d’eau par mol&ule de complexe. Le premier stade de decomposition consiste en la perte de l’eau de cristallisation; il est suivi d’une d&omposition totale du complexe anhydre, conduisant a l’oxyde metallique comme residu. ZUSAMMENFASSUNG Die thermischen Eigenschaften mit 2-, 3- und +Pyridincarbons%uren A.trctL.

CJrim.

R&z.

50 (x970)

79-91

der Komplexe von zweiwertigen Metallen wurden ermittelt mit Hilfe von TGA, DTA,

DSC, Hochtemperatur-Reflexionsspektroskopie und dynamischer Reflexionsspektroskopie. Die Komplexe fallen im allgemeinen aus Lijsungen als Hydrate aus mit r-5 Mol Wasser pro Mol Komplex. Die Zersetzung beginnt mit der Abgabe von HydratWasser, danach wircl der wasserfreie Komplex vollstandig zerstijrt und ergibt Metalloxid als Rtickstand. Jede Zersetzungsreaktion wird entspreclrend den angewandten thermoanalytischen Verfahren diskutiert. REFERENCES I B. G. COX, 2

3 ‘1 5 6 7 8 9 10

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