Solid complexes from mandelohydroxamic acid and several divalent metallic cations: a thermal and spectroscopic study

Thermochzmzca Actu, 127 (1988) 285-293 Elsevler Science Publishers B V , Amsterdam

285 - Prmted

m The Netherlands

SOLID COMPLEXES FROM MANDELOHYDROXAMIC AND SEVERAL DIVALENT METALLIC CATIONS: A THERMAL AND SPECTROSCOPIC STUDY

ACID

F SALINAS Department

of Analytical

I J PEREZ-ALVAREZ

Chemutn:

Fault)

of Saences,

*, J L MARTINEZ-VIDAL

Departments of Orgamc Chemistry * and Anabtrcal Unwersrty College of Almeria (Spam) (Received

Unrversrt~ of Extremadura

(Spam)

and A R FERNANDEZ-ALBA Chemutr),

3 August 1987)

ABSTRACT

Solid crystalline complexes of mandelohydroxanuc acid (MHA) and 12 metallic dlvalent cations have been obtained and characterized The determmed stolchlometrles are 2 (MHA) 1 (cation) for Mg(II), Ca(II), Sr(I1). Ba(II), Mn(I1). Co(H), Nl(II), Zn(II), Cd(II), Cu(II) and Pb(I1) and 1 1 for Hg(I1) The different water contents were measured and the thermal behavlour was studied by TG, CDS and IR spectrophotometnc techniques

INTRODUCTION

The ability of hydroxarmc acids to form complexes with metalhc cations has been extensively studled [l-3], however, there are only a few papers which describe the thermal behavlour and stab&y of such complexmg agents and their complexes m the solid state [4-71 Hydroxarmc acids generally form complexes of stolchlometry 2 1 with dlvalent catlons m neutral media, except m cases such as 5,5’-methylene-dlsahcylhydroxarmc and 5,5’-dlthlo-d1sallcylhydroxamlc acids, which lead to different stolchlometrles [8,9] Our purpose m this work 1s the synthesis of complexes derived from mandelohydroxarmc acid (MHA) and dlvalent metalhc cations, and to investigate the thermal behavlour of these solids by means of TGA-DTG, CDS and IR spectroscopic techniques 0040-6031/88/$03

50

0 1988 Elsevler Science Publishers

BV

286 EXPERIMENTAL

Materials MHA was synthesized followmg the method described by Hauser and Renfrow [lo] The isolated acid was recrystalhzed m petroleum ether methanol 2 1 All the MHA-dlvalent catlon complexes were prepared m this general way over 10 cm3 of a hot solution of 0 5 M MHA (as potassmm salt), 10 cm3 of 0 1 M solution of the correspondmg metallic salts were added with stirring The precipitate was lmmedlately filtered off, washed with cold water and dried over calcium carbonate Analytical data are shown m Table 1 Apparatus Elemental analyses were carried out at the Institute of Blo-organic Chemistry of Bircelona Thermal studies were carried out on a Mettler TA 3000 System provided with a Mettler TG 50 thermobalance and a Mettler dlfferentlal scanning calorimeter TG curves were obtained at a heating rate of 10 o C mm-’ m a static au atmosphere, using samples of weights between 5 81 and 11 61 mg The temperature range studied was 40-1000 ’ C m some cases and 40-800 o C m others The DSC curves were registered at a heating rate of 10°C mm-’ m a static atmosphere of an wlthm the range 30-600” C The sample weights varied from 1 24 to 1 71 mg m these cases

TABLE

1

Elemental

analysis data

Compound

MHA Mg(MHA), Ca(MHA), Sr(MHA) Ba(MHA),

C (%)

2H,O 2H,O z H,O 2H,O

H (%)

H,O

N (%)

(%) a

Calc

Found

Calc

Found

Calc

Found

Calc

5748 4890

57 46 47 84

5 38 5 09

5 37 5 10

8 38 7 13

8 40 7 13

9 20

14 06

47 04

48 00

4 90

4 66

6 86

6 95

8 82

16 82

43 87

4274

4 11

415

6 39

6 16

4 10

10 35

3802

3798

404

3 95

5 48

5 54

7 12

7 11

Found

Mn(MHA),

2H,O

45 59

45 60

4 75

4 71

6 65

6 64

8 51

8 64

Co(MHA),

1/2H,O

48 00

47 20

4 20

4 13

7 00

6 43

2 20

2 40

NI(MHA),

2H,O

45 00

4451

4 20

4 12

6 50

8 43

8 32

Zn(MHA),

2H,O

44 30

4467

4 62

4 55

6 46

6 33 6 33

8 31

12 72

Cd(MHA),

2H,O

7 49

7 36

Cu(MHA),

3996

3958

4 16

4 17

5 82

5 72

48 50

4701

4 04

4 34

7 08

6 61

Pb(MHA),

3559

3569

2 96

2 84

5 19

5 20

Hg(MHA)

2618

2676

2 18

1 86

3 82

3 78

A Water percentages

measured

from TG data

287

IR spectra were produced on a Perkm Elmer 297 spectrophotometer as KBr pellets prepared with the solids Just obtamed and after 1 h heating at 25, 80 and 150 o C

RESULTS AND DISCUSSION

The sohd MI-IA-metal complexes prepared m the specified experimental condltlons have a stolchlometry of 2 1 for all cations except Hg(I1) wbch forms a 1-l complex The complexes obtained from Pb(II), Hg(II) and Cu(I1) as well as MHA itself and its potassium salt crystallize without water of crystalhzatlon or coordmatlon (Table 1)

Fig 1 Thermogravlmetnc curves of mandelohydroxarmc acid complexes of (A) Mg(II), (B) Ca(II), (C) WI), (D) WII), (E) Mn(II), (F) Co(H), (G) NW), (H) Zn(II), (I) Cd(H), (J) Cu(II), (K) Pb(II), (L) Hg(I1) and mandelohydroxarmc acid (M)

\

I 100

300

500

700

900 TF-3

TEMPERATURE

Fig 1 (contlnued)

Hydrated complexes undergo a dehydration process between 40 and 140 o C (Fig l), and m the compounds from Mg(II), Ca( II), Sr(I1) and Zn(I1) this process overlaps with the pyrolysis, the mass loss m such

289 TABLE 2 TG asslgnatlons

for dehydration

processes Weight loss (4%)

Process

Mg(MHA), 2H,O Ca(MHA) 2 2H 2O Ca(MHA), H,O Sr(MHA), H,O Ba(MHA), 2H,O Mn(MHA), 2H,O Co(MHA), 1/2H,O Nl(MHA) 2 2H ,O Zn(MHA), 2H,O Cd(MHA), 2H,O

+ Mg(MHA), --) Ca(MHA), H,O --) Ca(MHA), --* Sr(MHA), --, Ba(MHA), + Mn(MHA)2 -+ Co(MHA), -+ Nl(MHA) z + Zn( MHA) 2 + Cd(MHA),

Calc

Found

9 20 441 441 4 10 7,12 8 51 2 20 8 43 8 31 7 49

14 06 4 42 1240 10 35 7 11 8 64 240 8 32 12 72 7 36

Temperature range (O C) 100-185 40-120 120-165 40-130 40- 90 60-140 60-140 40-140 loo-185 40-140

complexes being greater than that correspondmg to the loss of water only In the other compounds the percentages of mass loss are m good agreement ulth the calculated values Only m the Ca(I1) denvatlve can different hydration states be dlstmgmshed (see Table 2) Dehydration 1s accompamed, as expected, by an endotherrmc peak m CDS curves (Table 3), the involved energies being of 108 4 and 126 1 kJ mol-’ for the complexes of Mg and Zn In the complexes of alkahne-earth cations an inverse proportlonahty between dehydration temperature and lomc radius can be noted (see Table 2) Anhydrous complexes are stable wlthm a short temperature range, undergomg a strong decomposltlon m two or more steps as can be seen m Table 4. where the different temperatures correspondmg to mass losses and the expenmental and calculated residues (as percentages) are shown for the assigned decomposltlon processes MHA (and its potassmm salt) decomposes m a slrmlar way the first step (about 180 o C) corresponds generally to the greatest loss of mass (60%) and total decomposltlon occurs below 500 o C Most of the anhydrous compounds show a detectable stage at higher

TABLE

3

CDS data a Compound

Tl

HI

T2

Zn(MHA)z 2H20 Mg(MHA), 2H,O Pb(MHA) 2 Hg(MHA)

163 162 178

126 1 108 4 -1112

186 193 192 200

a T, are gwen m o C and H, m kJ mol-’

H2

-454 -468 -954 -1427

r,

276 270

H3

-614 -556

290

TABLE 4 TG asslgnatlons

for the pyrolysis

Process

processes

Temperatures

Mg(MHA) 2 MgCO, Ca(MHA) 2 CaCO, Sr(MHA) 2 SrCO, Ba(MHA) z Mn(MHA), Co(MHA) 2 coca, coo Nl(MHA), NlCO, Pb(MHA) z Zn(MHA), Cd(MHA) 2 CdCO, HgMHA Cu( MHA) 2 cuco,

+ MgCO, + MgO + CaCO, + CaO --f SrCO, -+ SrO + BaO + MnO - CoCO, + coo + co,04 + NICO, + N10 - PbO + ZnO + CdCO, - Cd0 + pyrolysis + CuCO, --) cue

T *, temperature

(O C)

195,300 510 165,280,420 680 140,260,500 880 140,520 160,262,480 170,262,375 485 180,262,370 530 180,420,530 185,310,500 160,265,410 620 160,265,410 221 450

at whvzh the residues

Residue ( W)

T*

Calc

Found

21 41 10 27 24 50 13 75 35 37 23 67 30 34 16 77 29 75 18 72 20 06 27 82 17 55 4139 1877 35 88 26 72

19 82 10 35 23 82 1393 33 77 23 81 30 02 16 85 26 18 18 52 20 71 25 30 17 81 4140 17 81 33 39 27 31

950

3120 24 91

30 73 23 10

800

800 950 950 800 950 520 950 950 800 800

were measured

temperatures m wluch the correspondmg carbonate seems to be formed before total oxldatlon, and the measured percentages of residual masses are m good agreement with the calculated values The complexes denved from Cu(II), Zn(II), Nl(II), Co(U) and Mn(I1) follow the thermal stability order proposed by Irving and Wllhams [ll] MnZn IR data are shown m Table 5, where a stift of the C=O stretching band (1660 cm-’ for free MHA) to lower wavelengths (80-30 cm-‘) occurs and simultaneously there 1s a shift toward higher wavenumbers (about 40-30 cm-‘) m the C-N bending band m all the solid complexes whle the N-H stretchmg absorption 1s shfted m a smular way, although these variations are not as large as those of complexes m which N-H bond 1s directly involved [12] The rest of bands seems to remam unaffected and all the data agree with the formula Me/2

Fh-CH(OH)-/ \

NH -

I

0

of m which a partial loss of double bond character due to the partlclpatlon the carbonyl group m the chelation (and also due to a certain double bond

.

K-MHA,

(MHA)Hg

3450b _ _

_

3450b 3400b 3460b -

3450b 3400b 3520b 3500b 3500b 3400b 3460b _ 3200b 3235 _ 3200b

3265 3248 3200b 3200b 3235 3212 3225

3200b

3280 3480

150°C

3232 3210b

3280 3260

20°C

150°C

3440b -

20°C

3440b -

N-H

O-H

potassmm mandelohydroxamate

MHA K-MI-L4 (MHA),Mg 2H,O (MHA),Ca 2H,O (MHA),Sr H,O (MHA),Ba 2H,O (MHA),Co 1/2H,O (MHA),Nl 2H,O (MHA),Zn 2H,O (MHA),Pb (MHA),Cd 2H,O (MHA),Cu

Compound

IR absorption bands (cm-‘)

TABLE 5

1580

1630 1632 1612 1615 1620 1605 1612

1619 1630

1660 1630

2o”c

c=o

1580

1615 1620 _ _

1619~ _

1720 _

150°C

-

1535 1535 1554 1515 1545 1515 1512 1555 1518 1545 _

20°C

N-H

_ 1512 1555 _ _ _ _

1535 _ _

150°C 1343 1310 1382 1382 1342 1386 1380 1385 1383 1383 1382 1369 1390

2o”c

C-N

_

1310 _ _ 1385 1383 _ 1369

150°C

1008

1020 1025 1030 1030 1032 1028 1010 1026

1023 1010 1032 -

2o”c

N-O

990

975 994 989 980 985 985 985 993 985 987 -

150°C

-

1030 1032 _ 1026

1023 _

-

985 993 _ _ _

_

292

I

I 2

3

4

Log

KML2

Fig 2 Relatlonshlp between Av (vC=O band shifts of the complexes m comparison to free hgand) and log KMML,regarding the Mn, Co, Nl and Cu complexes

character of the C-N linkage as a result of electron withdrawing effects) Justifies the measured shfts [13,14] A single exception among the compounds studied 1s the MHA-Hg(I1) complex with 1 1 stolchometry the carbonyl band has been changed for a new absorption (1528 cm-‘) that has been assigned to a C=N stretchmg band So a different formula has to be written for tbs 1 1 complex O______& /

I Ph-CH(oH)-C\\ &_____O

Most absorption bands are strongly affected by temperature In consequence the whole spectrum changes, and the bands disappear or become such weaker after heating for 1 h at 150” C m all the complexes studied, except m the Nl, Zn and Cu compounds In the potassium salt a new sharp band appears after 1 h heating at 150 ’ C, around 2160 cm-‘, corresponding to a O=C=N- group [14,15] Dehydration processes were also detected by comparmg the spectra obtained at different temperatures A linear relationship between stability constants [16] and the sift of the C=O band could be found m the Mn, Co and Nl complexes (Fig 2)

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