Complexes of uranyl ion with potentially tridentate ONO schiff bases

INORG. NUCL. CHEM. LETTERS Vol.16, pp.109-115. © Pergamon Press Ltd. 1980. P r i n t e d in Great B r i t a i n .

002U-lbS0/80/0301-0109502.00/0

C O M P L E X E S OF IJRANYL ION WITH P O T E N T I A L L Y T R I D E N T A T E ONO SCHIFF BASES. G . D i a , V . Luparello, F .Maggio, T . P i z z i n o , V .Romano G r u p p o di C h i m t c a di C o o r d i n a z i o n e , U n t v e r s i t & di P a l e r m o , V i a A r c h t r a f t 28, 90123 P a l e r m o ( I t a l y ) . G .Bocchi [ s t t t u t o di M i n e r a l o g i a e P e t r o g r a f i a , U n i v e r s i t & di B o l o g n a , P i a z z a S . D o n a t o 1, 40127 B o l o g n a ( I t a i y ) .

The s y n t h e s i s and c h a r a c t e r i z a t i o n of c h e l a t e c o m p l e x e s of t r a n s i tion m e t a l s and o r g a n o m e t a l m o i e t i e s have b e e n s u b j e c t of many i n v e s t i g a t i o n s in o u r l a b o r a t o r y ( 1 - 6 ) . R e c e n t l y we have e x t e n d e d the r e s e a r c h to the a c t i n i d e g r o u p and s i n c e it is w e l l known that s p e c t r a l and m a g n e t i c d a t a a r e of l i t t l e help in c l a r i f y i n g the s t r u c t u r e of t h e i r c o m p l e x e s , we have c a r r i e d out a complete s i n g l e c r y s t a I a n a l y s i s of the compound d i o x o - N - ( o - h y d r o x y p h e n y l ) s a l i c y l i d e n e i m i n a t o u r a n a t e ( V I ) d i h y d r a t e (7). In this p a p e r we r e p o r t the s y n t h e s i s and c h a r a c t e r i z a t i o n (by e l e m e n t a l analy s i s , IR, UV r e f l e c t a n c e s p e c t r a , t h e r m o g r a v i m e t r i c and t h e r m a l d i f f e r e n t i a l a n a l y s i s ) of the c o m p l e x e s of the u r a n y l ion with the p o t e n t i a I l y t r i d e n t a t e d i b a s i c S c h i f f b a s e s N - ( o - h y d r o x y phenyl)salicylideneimine (H2SAP) ,

N-(o-hydroxypheny[)3 m e t o x y s a l i c y l i d e n e -

tmine (H2VAP) , N - ( o - h y d r o x y p h e n y l ) 5 , 6 b e n z o s a l i c y l i d e n e i m i n e (H2NAP) and i t s i s o m e r N ( o - h y d r o x y - 5 , 6 b e n z o p h e n y I ) s a l t c y l i d e n e i m i n e (H2SAN).

Experimental Preparation of ligands. The ligands H 2 L were prepared by mixing equimolar amounts of o-aminophenol and salycilaldehyde (H2SAP) (H2VAP) , 2-hydroxy-l-naphthaldehyde (H2NAP)

(8), vanillaldehyde

(9) and salicylaldehyde with

1 -amino-2-naphtol (H2SAN). The solids obtained by cooling were recrystallized from ethanol to yield red crystals melting at 185°C (H2SAP) , 200 ° C (H2VAP), 25£°C (H2NAP), 215°C (H2SAN). P r e p a r a t i o n of c o m p l e x e s

The uranyl complexes were preparaed by mixing water-methanol solutions 109

Complexes of Uranyl Ion

II0

of e q u i m o l a r amounts of UO2(CH3COO) 2 - 2 H 2 0 and the r e s p e c t i v e l i g a n d . A f t e r r e f l u x i n g f o r some h o u r s , s m a l l c r y s t a l s h a d r e c r y s t a l l i z e d f r o m the e t h a n o l . T h e s e w e r e pump f i l t e r e d and d r i e d . P r i o r to a n a l y s i s , t h e y w e r e d r i e d o v e r s i l i c a g e l u n d e r v a c u u m to c o n s t a n t w e i g h t . T h e y a r e r a t h e r i n s o l u b l e in m o s t s o l v e n t s . z~la[~sis

The uranium content of the complexes was determined by igniting a known weight of the complexes to U 3 0 8 at 800°C. Elemental analysis of C , N , H was made by Kurt Eder Laboratory (Gen~ve). The analytical data are summarized in Table I.

TABLE

I

E l e m e n t a l a n a l y s i s of d i o x o u r a n i u m ( V l ) - L c o m p l e x e s .

Complex e s (Empirical formula)

U% Calcd. Found

C% Calcd. Found

H% Calcd. Found

N% Calcd. Found

U 0 2 S A P "2H 2 ° (CI3HI3NO4U)

49.0

47.6

32.2

31.2

2.70

2.64

2.88

2.90

U O 2 V A P •2 H 2 0 (CI4HI6NO5U)

46.1

/-~.9

32.6

31.8

3.13

2.58

2.72

2.79

UO2(HNAP)2

29.9

30.1

51.4

51.2

3.02

3.i0

3.52

3.63

29.9

29.8

51.4

50.0

3.02

3.08

3.52

3.32

(C34H24N 2 0 6 U) UO2(HSAN)2 ( C 3 4 H 2 4 N 2 0 6 U)

Physical measurements IR spectra of the ligands and complexes in nu]ol or hexachlorobutadiene mulls -i w e r e recorded on a Perkin Elmer/+57 instrument in the 4000-650 c m range. Diffuse reflectance spectra were measured by using a B e c k m a n D K 2 A spectro photometer equipped with the special attachment. M g O

w a s used as reference.

Thermogravimetric analysis ( T G A ) w e r e m a d e by using a C A H N

electrobalan-

ce model R G and an anlinductif vertical furnace (i0) in an air stream maintained at 1 aim. pressure. The temperature of the furnace w a s increased with a constant rate of 3.3°C per min. by using a Leeds and Northrup C . A . T . unit. The thermograms were corrected for the buoyancy effects. The thermodiffe-

]ll

Complexes of Uranyl Ion rential analyses (DTA) were carried out by a microanalyzer made by the ]Bureau de Liaison. The small differences in the temperature at which the thermal effects in T G A

and D T A

take place, are due to the fact that in the

T G A furnace the thermocouples were not in direct contact with the sample but at short distance (3 cm.).

Results and discussion a dark red compound

In the reaction between UO2+9_ and H 2 S A P containing two water molecules U O 2 S A P . 2 H 2 0 of two water molecules was found by T G A

was obtained. The presence

and D T A .

At 150 ° C the compound

undergoes a weight loss of 6.86% (theoretical 6.96% for two water molecules while at 400°C the loss is ~5.6%. The remaining product amounting to 54.~% of the initial sample weight is U 3 0 8 (theoretical ~ . 3 % ) . T w o endothermic peaks at 123 ° C and 158 ° C confirm the presence of two water molecules. These appear at a much lower temperature than the begin of the decomposilion to U308, which is exothermic and takes place between 340 ° C and 400°C. The presence of two water molecules is m agreement with the X ray single c.rystal structure analyses carried out on this compound (7). The approximate coordination is pentagonal bipyramidal. It is reached by using the O N O of the ligand and the oxygen of the two slightly differently bonded water

set mo-

lecules forming all together a puckered pentagonal base crossed at its center by the uranyl axis (Fig. i). It seems the most c o m m o n coordination for uranyl complexes (II). Evidence for the presence of two water molecules, although not conclusive, is also obtained from the elemental chemical analf~ses data (Table I). For this reason only, different hydrates of different composition, UO2SAP-xH20

, were previously reported (12). The similarities exhibited by the IR spectra of H 2 S A P , H 2 V A P ,

H2NAP

, and H 2 S A N

in the solid state (Table IO clearly indicate c o m m o n

structural features. Since the IR

spectrum of H 2 S A P

in the solid state has

been interpreted in terms of a dimer structure with inter and intramolecular hydrogen bonds (13), we suggest a similar structure for H 2 V A P , H 2 N A P H2SAN

(Fig.l). The fact that H 2 S A P , H 2 V A P , H 2 N A P

and H 2 S A N

and

have si-

milar reflectance spectra supports this view. The IR spectrum of U O 2 S A P " - 2 H 2 0 (Table II) exhibits a broad band centered at 3400 c m -I in the O H stretching region due to the two water molecules and no band in the region where the O H

band for the free ligand (2550 c m -I) appears. The conjuga-

ted C = N appears at 1605 c m -I while in the free ligl~nd is at 1635 c m -I , the

I12

Complexes of Uranyl Ion

~.~.

o _uo ./

,,'\ /\

....... i% Fig.l

Schematic

sketch

of:

(a)

(c)

H2NAP

one

of

in

the

\o/ \o""

H2SAP ; (d)

the text

of

; (b) UO 2

the

structure

UO2SAP.

2H20;

(HNAP)2.

Only

two

forms

mentioned

is

shown

for

UO 2

(HNAP) 2 .

lowering being due to the decrease of the bond order of carbon to the nitrogen link following the coordination of the imine nitrogen to the uranyl ion. M o r e over a C - O frequency can be detected at 1292 c m -I higher than that in the -1

free ligand where it appears at 1280 c m m agreement with what reported -i (14). The two bands at 839 and 920 c m can be attributed to the Ylsym and Y3 asym 0=]5=0 stretching

vibrations (15).

In agreement with the similarity of H 2 V A P nyl complex of H 2 V A P

and H 2 S A P ,

has a similar formula: U O 2 V A P - 2 H 2 0 ;

the ura-

the thermal

properties are similar (loss of two water molecules nearly complete at 243 ° where the oxidation,which takes place exothermically between 2/+3= and about ~00 °, starts suddenly) and similar is the infrared behaviour (Table li). F r o m these data w e infer similarity of structure for both U O 2 S A P

" 2 H 2 0 and

U O 2 V A P •2H 2 ° . The two complexes, obtained from the reaction between U O 2+ and the two isomers H 2 N A P

and H 2 5 A N ,

have

the same formula but have a com-

position different from the ones obtained with H 2 5 A P

and H 2 V A P .

Actually

both m a y be formulated as U O 2 L ' H 2 L or U O 2 ( H L ) 2 without any water molecule in both cases. In agreement with this the D T A

curves show for both com-

pounds only the two exothermic peaks in the range 300 °-400 ° due to the oxidation of the compounds to U308, as confirmed by the residue weights relation (theoretical 35.8% found 36.1%

of the starting sample) and no sign of

water molecule loss. Comparison of the IR spectra of the complexes with tho-

Complexes

i

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of

Uranyl

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114

Complexes of Uranyl Ion

se of the ligands H 2 N A P

and H 2 S A N

shows also an O H stretching in the ran-

ge 3350-3300 cm -I , the C = N frequency practically at the same wavenumber in both complexes and corresponding ligands. If w e assume that in each complex the two bonded ligands are

equivalent and that the imine nitrogen is not co-

ordinated to the uranium, it is easily understood that a single C = N frequency appears which is practically identical in both complex and corresponding ligand. So w e suggest, for the two complexes, the formula U O 2 ( H L ) 2 with a square bypiramidal structure reached by using only the oxygen atoms of the H L - ligands in agreement with the great affinity of uranyl for oxygen contail~ing ligands (Ii). In conclusion, among the four potentially tridentate Schiff bases reported in this investigation, those not containing the naphtalene ring, behave towards the uranyl ion just as reported for many other metal cations and organo cation, i.e. as dibasic tridentate ligands, while the two isomers H2NAP

and H 2 S A N

containing the naphtalene ring behave towards uranyl ion

as monobasic bidentate ligands, resonance making probably meaningless which O H group of the ligand dissociates. This behaviour can be due to the great electron withdrawing property of the naphtalene ring as suggested for similar ligands used in complex formation with Ni(ll) (16). X ray measurements on U O 2 ( H N A P ) 2 and U O 2 ( H S A N ) 2 crystals are in progress in our laboratory to confirm this behaviour leading to an u n c o m m o n uranyl coordination (ii). References i

F.Maggio, R.Bosco,F.Bonati

and R.Barbieri, Inorg.Nucl.Chem. Letters,

4, 73(1961). 2

V.Romano, F . M a g g i o and T . P i z z i n o , J . I n o r g . N u c l . C h e m . , 3_33, 2611(1971).

3

V.Romano, R . B a d a l a m e n t i , T . P i z z i n o and F . M a g g i o , ] . O r g a n o m e t a l . C h e m . , 42~ 199(1972).

4

F . M a g g i o , T . P i z z i n o , V.Romano and A . G i o v e n c o , I n o r g . N u c l . Chem. L e t t e r s , 9 , 639(1973).

5

F . M a g g i o , T . P i z z i n o and V.Romano, I n o r g . N u c l . C h e m . L e t t e r s , 1___0,1005(1974).

6

F . M a g g i o , T . P i z z i n o , V.Romano and G . D i a , J . I n o r g . N u c l . C h e m . , 38,599(1976)

7

V . L u p a r e l l o , V . R o m a n o and L . R i v a S a n s e v e r i n o , in p r e s s .

8

M . C l a a s z , B e r . D t s c h . Chem. G e s . 4 9 , 11/+1(1916).

9

A. Senier a n d R . C l a r k e ,

10

].Chem. S o c . , 99 , 2082(1911).

G.Bocchi,M.CaraDezza and L . R i v a di S a n s e v e r i n o , Rend. A c c . N a z . L i n c e i 43, 568(1967).

11

L . C a t t a l i n i , U . C r o a t t o , 5 . D e g e t t o and E . T o n d e l l o , Inorg. Chim. Acta, Rev. 5 , 19(1971).

Complexes of Uranyl Ion

12

V.V.Zelentsov, Russ.J.Inorg. Chem., 8_, 126/4(1963).

13

F.Urrland, B.K.Poddar and H.Stegermeyer, Z.Analyt. Chem., 216, 125(1966).

1/+ E.Kovactc, Spectrochimica Acta 23A~ 183(1967). 15

J. Selbin, Angew. Chem. , 5 , 712(1966).

16

A. Syamal, J.lnorg.Nucl. Chem., 39 , 1565(1977).

115