JOURNAL OF THE AMERICAN CHEMICAL SOCIETY (Registered in U. S. Patent Office)
(0Copyright,
1961, by t h e American Chemical Society)
JUNE 2, 1961
C O L U M E 83
NUhlBER
10
PHYSICAL AND INORGANIC CNEMISTRY [CONTRIBUTION FROM
THE
DEPARTMENT O F CHEMISTRY O F
THE
STATE USIVERSITY O F IOWA,
IOWA
CITY, IOWA]
111. X-Ray Diffraction Studies of Several Stable Phases BY N. C. BAENZIGER, H. A. EICK,H. S.SCHULDT AND L. EYRING
Terbium Oxides.
RECEIVED NOVEMBER 5, 1960
A previous study' involving tensiometric measurements, differential thermal analysis and cursory X-ray diffraction analysis revealed intermediate stable phases in the terbium-oxygen system between the sesquioxide2m3and the dioxide.* Previously, many observations of a brown higher oxide of terbium had been made and the formula Tba07 had been given to Work done in these Laboratories,1-8however, failed t o reveal any special stability for a composition TbOl.7j, and it is believed t o arise from a slow oxidation of a lower oxide when the latter is cooled in air or oxygen. The present work was undertaken to clarify the various stable phases existing in this oxide system using previous work as a guide in sample preparation.
Experimental Part Materials.-The terbium (99.9+ yo pure) was obtained from Dr. F. H. Spedding, Ames Laboratory of the U.S.A.E. C., as oxide. Reagent grade chemicals were used in the dissolution of these oxides, precipitation of terbium as the oxalate and other procedures in the preparation of fresh oxides. Commercial tank oxygen was used to prepare the higher oxides. Preparation of Samples.-Specimens with oxygen content not greater than TbOl.81, were made using molecular oxygen. Compositions between Tb01.827 and Tb01.81 were prepared in an autoclave operating under an oxygen pressure of up to 600 atmospheres and a temperature up to 425". For compositions below Tb01.81 the oxides were treated in a platinum lined reactorg capa le of operation a t 10 atmospheres at 1100" or in an appara us1o incorporating an automatic recording thermobalance. Samples with oxygen content greater than Tb01.83 were made by treatment with atomic oxygen in a discharge tube.*J1 All samples were cooled as rapidly as the apparatus would permit after the desired composition had been reached. No appreciable weight change occurred in those experiments where analyses could be made. Previous observations1
!
(1) E. Daniel Guth and L. Eyring, J . A m . Chem. Soc., 7 6 , 5242-5244 (1954). (2) W. H. Zachariasen, P h y s . Rev., 73, 1104 (1948). (3) V. M. Goldschmidt, F. Ulrich and T. Barth, Malem.-Naluusich, Klasse 1925, N o . 5 , p. 5 ; C. A , , 19, 2764 (19251. (4) D. M. Gruen, W. C . Kohler and J. J. K a t z , J . A m . Chem. Soc.. 73, 1475 (1951). ( 5 ) R. Marc, B e l . , 36, 2382 (1902j. ( 6 ) R. J . Meyer and M. Ross, ibid., 36, 3740 (1902). (7) Prandtl and Rieder, Z. anorg. Y. allgem. Chem., 938 225 (1938). ( 8 ) Wilbur Simon and LeRoy Eyring, J . A m . Chem. Soc., 7 6 , 5872 (1954). (9) C . L. Sieglaff and L. Byring, i b i d . , 79, 3024 (1957). (10) A. Ostroff and R. T . Sanderson. J . I n o r g . Nuclear Chem., 9 , 45 (1959). (11) H. A. Eick, P h . D . Thesis, State University of Iowa, 1956.
imply that no new phases are introduced in this quenching procedure. The composition of the oxides was always determined by observing the weight loss between the oxidized material exposed to oxygen as described above and the sesquioxide. The sesquioxide is formed by reduction of a higher oxide with hydrogen a t 650' for 15 hr. X-Ray Analysis.-Powder diagrams were obtained in a 114.6 mm. Norelco powder camera. Diffractometer traces were produced using a Norelco diffractopeter. Iron radiation (Aa, = 1.93597 A . , A,, = 1.93991 A. and Xg = 1.75654 A.) was produced by a General Electric XRD5 unit. ~
Results and Discussion Figure 1shows the phases which have been identified in the terbium-oxygen system in this study. TbOl.boo prepared by reduction in Hz as described above is a body-centered cubic structure (a = 10.7281 ZI= 0.0005 B.)with only a small range of solid solution. It has the Mnz03(bixbyite) structure and is isostructural with many other rareearth sesquioxides. The bixbyite structure results from the ideal fluorite type structure upon the ordered removal of one-fourth of the oxygens from eight unit cells of the parent fluorite type. A sample melted on a tungsten strip in high vacuum was observed to be the monoclinic R type. As oxygen is added to the b.c.c. material, a second phase of composition Tb01.715 appears. There is a miscibility gap between these phases a t temperatures as high as 750'. Neither phase shows an appreciable range of solid solution. The X-ray diffraction pattern of this phase is very similar to that for a face-centered cubic fluorite-type phase except that some of the lines have split into
2219
N. C. BAENZIGGR, H. ,4. EICK,H. S. SCHULDT AND L. EYRINC
2220 I
Tb
TbO1.81 + I (tricl) ' TbOl.sa + (rhomboliedral)
TbO1.a + x(i (b.c.c. or monoclinic B type)
I 1 TbOl.i2 -
ya
Pr01.60
Vol. 63
l
i
I I
(rhombohedral) (hexagonal or b.c.c.)
+
PrOl,Y2 -
CeOl.m
+
CeOl 7z
-
(rhom)
(rhombohedral)
I
(hexagonal or b.c c.)
(rhom)
1
Ce01.72
(rhombohedral)
(f.c.c.) CeO1.78 + I. (rhom)
+
PrOl.sa +
(f.c c.)
-
(f.c.c.)
Pro2 00
,
CeOl.sl + (rhombohedral)
(rhom)
CeOl.xl
-
Ce02 oo (rhom)
-
(f.c.c.)
I I I I I I I I I I I 1.50 1.60 1.80 1.70 1.90 2 00 Fig. 1.-Schematic representation of the regions of stability in some rare earth-oxygen systems. The symbols x and y are to signify a range of composition which is dependent on both composition and temperature. cubic symmetry and allow the rhombohedral distortion which is observed. The cell contents now become Tb7012 or Tb01.714, in excellent agreement with the analytical determination of the composition. TABLE I Cell axes5 based on the cubic CaFz axes
Number of M atoms/ cell
Cell axes" based on the cubic CaFz axes
a' a' 15 a/2 b/2 1 a-b+c 10 2 3a/2 b c/2 a -F b/2 c/2 20 4 b 2c 2a a 26 2a 4 b/2 - c/2 3a/2 f b 3cj2 2fj 3a/2 b/2 c 2a 3b/2 3c/2 5 2ti 5a/2 3b/2 + c 7 a - b/2 c/2 27 7 2u b / 2 f c/2 5a/2 f 5b/2 2c 2; 3 a / 2 f 3c/2 8 a f b 28 5b/2 4- 5c/2 8 b/2 2c 3a 3a/2 28 2a - b 9 3a/2 f b f c / 2 28 3a 2b + 26 5a/2 3b/2 26 9 a - 3b/2 3c/2 31 3a/2 b/2 13 32 2u 3a/2 c/2 14 32 3n 36 2c 16 2a+b+c b' and c' axes may be obtained by cyclic pcriiiut.ttic~ri of the a , b and c of a'.
+
- -+
-+
+ + +
+
+ +
-
+
+
+
- - _- - - -.. FIE. !2.-Rhombohedral cell of Tb7012 The cell is outlined- with rods; the shaded circles ;;present T b atoms associated with the rhomb. cell. __
.
-
-__
doublets or triplets and a few additional weak lines occur. The splitting of the fluorite-type lines can be accounted for on the basis of a rhombohedral pseudo cell, a0 = 5.319 i 0.0018.,a = 89' 41.2', which is only a slight distortion of the ideal fluorite type cell, In order to account for the weak additional lines, the rhombohedral cells (and their related hexagonal cells) listed in Table I were considered. I n this table, only the a' axis is given; the b' and c' axes may be obtained by cyclic permutation of a, b and c in a'. The smallest cell which will explain the weak reflections has a' = u - b/2 c/2, b' = ~ / 2 b - C / 2 , C' = - % / 2 b/2 c, with a volume 7/4 times the fluorite unit cell. Table I1 shows the comparison of the observed l/d2 values with those calculatedoon the basis of this cell with u = 6.509 i 0.002 A., a = 99' 21' f 0.5'. The relationship of this unit cell to the fluorite cell is shown in Fig. 2 . The ideal rhombohedral angle is 9 9 O 36'. The rhombohedral cell would contain 7 terbium atoms and 14 oxygen atonis if the composition were TbOz and the structure were the ideal fluorite structure. Removal of two oxygen atoms along thc three-fold axis of the cell would destroy the
+
+
+
+
Number of hl atoms/ cell
+ -
+
+
+
-
+
+
+
+-
-+
+ +
If monophasic Tb01.716 is further treated with oxygen, a new phase appears which becomes the only phase observed a t a composition of TbOl.81. A miscibility gap between TbOl71 and TbOl81 is present a t temperatures below 450'. X-Ray diffractometer patterns show that the fluorite type lines are split in a different way. The fact that the cubic (lll), (220) and ( 2 2 2 ) lines are split into three lines whereas (200) and (400) reniain as single lines eliminates distorted cells based on the rhombohedral system or mixtures of rhombohedral phases with different cell dimensions. A possible triclinic cell which explains the splitting of the lines reasonably well, both in position and in a relative intensity (due to multiplicity alone), as shown in Table 111,has the dimensions a = b = c = 5.286 + 0.001 A.,ct = p = 89' 25', y = 90'. (A tetragonal cell with a' = -\I 2 u/2, c' = 9Sa or an end-centered monoclinic cell with a' = b $. c, b' = b - L , c' = -u', is equivalent to this triclinic cell.) Not all of the splitting is well resolved a t higher angles in the diffractometer patterns. The triclinic cell
222 1
X-RAYDIFFRACTION STUDIES OF TERBIUM OXIDE
May20, 1961
TABLEI1 OBSERVEDA N D CALCULATED l/&VALUESFOR TbrOl~(ThO1.714) lld2 = 0.025197 (ha k* P) 0.009770 (hk kl hl) Q+ = 6.509 f 0.002 A,, a = 99" 21' f 0.5'
+ + +
Intensities0
Indices
-110 111 200
0.02520 .04062 .06015 .06581 .lo078
111 210 211 211 210
.lo490 ,10644 .12187 .14141 .14551
210 221 211 3io 300,22i
.16249 .18769 .20004 .22266 .22677
511 220 222 320 3i1
.22831 .24066 .26327 .26593 .27805
310 321 821 221 311
,28128 .28436 .30389 .30494 .34555
522 32i 330 411 320
.35015 .36252 .36561 .38515 .38617
100
iio vw
S
m vw vw
m m vW
-l/dCalcd.
Ohsd.
Intensitiesn
vw 0.06005
.lo656
.14143 ,14551 .I8779
vvw vw
vvw
vvw .28152 .28461 ,30365
vvw
niw mw mw
+ + Indices
Calcd.
Wi
0.44371 ,46022 ,46639 .46743 .47051
32 1 332 410 421 422 33i 430 331 33 1
In
permits additional weak reflections to occur (omitted for simplicity from Table 111) which were not observed in the diffractometer patterns. Weak reflections were observed in DebyeScherrer films but with insufficient accuracy to determine the true unit cell. On the premise that an ordered removal of oxygen atoms from the parent fluorite structure is responsible for this phase, the simplest stoichiometry corresponding to the triclinic phase is TblaOaeor TbOt.az. Oxides obtained by treatment in an autoclave were either a pseudo-triclinic Tb01.81or a pseudorhombohedral phase depending on whether the resulting composition was less or greater than Tb01.82. The absence of observations of two phases in any one sample must be due to the small composition change and the proximity of lines from each phase. The phase of highest oxygen composition obtained in these experiments with molecular oxygen is Tb01.627. Diffractometer patterns
Obsd.
0.45931
.a8748 .ti0805 ,5126'7 ,52501 .52810
411 421 42i 422 420
.54147 .54764 .54866 ,56563 .582 10
322 311.833 332 510 331
.58467 .59238 .59392 .60626 .62528
52 1 500 520,492 340 421
.62889 .62991 .63300 ,64996 .66591
5ii 34 1 52 1 510 550,333
.67054 ,67516 .68750 .70397 ,71013
.66990 .67494
,71117 .71578 .74715 .75486
.71066
niw 432 310,322 .38926 .38913 531 -39081 .39057 33 1 430 .40315 400 531 222 .41959 420 .42538 .42577 W 32 1 .43143 .43122 VW a Symbols used (in decreasing intensity): s = strong, ms = medium strong, m = medium, weak, vw = very weak, vvw = very very weak.
m
l/d¶
.54823 .56590
.59244
.62514
.63303
.'io414
mw = medium weak, w =
have been indexed as a rhombohedral pseudo cell with a = 5.283 f 0.001 A., Q = 89' 41'. A comparison of calculated and observed l / d 2 values is shown in Table IV. It is reasonable to expect that this cell is also associated with a specific stoichiometry, corresponding to the ordered removal of oxygen atoms from the ideal fluorite structure. Possible metal-oxygen ratios based on rhombohedral cells derived from the fluorite structure are listed in Table V. Although TbBOsl corresponds to the experimental composition, additional weak lines, absent in the diffractometer traces and extremely weak DebyeScherrer films, could not be reliably explained by that unit cell. Specimens obtained from treatment with atomic oxygen show a fluorite lattice with an avera e composition of Tb01.95 and Q. = 5.220 0.001 . Table VI summarizes the results of the X-ray analyses. Five distinct phases of considerable stability and with only liniited solid solution have
*
1
N. C. BAENZIGEM, H. A.EICK,H. S . SCHULDT AND L. EYRING
2222
OB5EKVEU
+
1/d2 = (hz = b = c =
/I
Intensi tiesa
TABLE 111 CALCULATED l/d2 VALUES FOR TbOl.sOg k z +P) (0.0357F5) (2kl 2hlj (0.000358) 5.286 i 0 001 A , . 01 = 0 = 89"25', y = 90'
AND
Cubic indices
+
Triclinicindices
l/d2
0.10592 .lo730 , 1057Y
0.10580 10720 ,10866
200
200
,14314
,14314
220
2orl,02" L'20,220 202,022
.28i341 .28628 ,28915
,28313 ,28618 ,28898
II1
ins
Obsd.
1ii 111,111 111
ms 111s
l/d' Calcd.
111
ms S
+
Ill
311, 131 113
.38933 ,39077 ,39270 . 39363 ,39507 ,39650 ,39793
222 222,222 222
,4236'3 ,42942 ,43515
400
400
.572,56
,57254
,67132 .675Gl .B i g 9 1 .68422 ,68851
,67065
33 1
133,312 33% 133,513 - 331,331 i33,331,3i3 133,313
0 ~ 2 , 0 2 4 , 4 0 2 , ~ 0 4 ,70997 mw m 420 420,240,420,240 .7157O 402,042,204,0%1 mw .72143 Symbols used same as in Table 11.
,70973 .7 156s ,72056
311,121
Ill
Tin, 113 .?ii, 131
311 rn
w mw
222
W
m W
niw
mw
,39246 ,39461
,42337 ,42939 ,43624
.Gici49
GM89
TABLE IV OESERVEDAND CALCULATED l/dz VALUES FOR TbO,.,,, 1 ' d 2 = 0.35838 ( h z k 2 2') a 0.0004023 (hk kl hlj u = 5.283 I 0,001 A , a = 89"41'
+ +
Inrensi- In- -l/dz-t i e s a dices Calcd. ms 111 0,10631 s 111 ,10774 ,14335 ms 200 m 220 ,28510 220 ,28832 m miv 311 ,39142 3il ,39462 rn 311 ,39623 17 222 ,42524 ,43167 w 122 m 400 ,57342 m w 331 ,07493
Obsd. 0.10613 .lo768 ,14310 .2851? ,28838 .3916S .39521
+ +
Intensitiesa mv m rnw mw w
m m
Indices 33i 391 420 I20 422 412
422 333 511 5ii 38.1, 511
.Id=---. Calcd. Obsd. 0,67972 0.67862 b845.5 ,68363 ,71355 ,71281 .71999 ,71935 85209 ,85115 .86173 ,86128 .86495 ,86392 ,95679 ,96304 ,96323 ,96804 ,96713 ,97120 ,97022 -1
Vol. 83
TABLE V
STOICHIOMETRIES BASEDON RHOMBOHEDRAL UNIT CELLS Metal
4 5
"
7 8 8 9 9 13 13 13 14 16 16 19 19 19 20 20
Oxygen
. I
9 12 13 13 15 16 17 22 23 24 25 27 29 33 34 35 34 37
Ratio
Metal
Oxygen
Ratio
1.780 1,800 1,714 1.857 1,625 1.875 1.778 1.889 1.692 1.769 1.846 1.786 1.687 1.812 1.737 1.789 1.842 1.700 1.850
25 25 25 26 26 27 27 27 27 28 31 31 81 31 31 32 32 32
43 44 46 45 47 46 47 49 50 51 53 54 55 56 57 65 57 59
1 . T20 1.760 1.840 1.731 1.808 1.704 1.741 1.815 1.852 1.821 1.710 1,742 1 .774 1.806 1.839 1.719 1.781 1.844
TABLE VI SUMMARY OF CRYSTALLOGRAPHIC RESULTS ON THE TERBIUXOXYGEN SYSTEM Composition Major phase Tbol.300 Body centered cubic a = 10.7281 =t0.0005
A.
TbOl.601 Body centered cubic a = 10.7281 i 0.0005
A.
Minor phase
Rhombohedral a' = 6.509 i 0.002 A. a = 99' 21' =k 0.5' Pseudo-cell a = 5.319 f 0,001 A. a = 89' 41.2'
TbOl.713 Rhombohedral a' = 6.509 i 0.002 A. a = 99' 21' i 0.5' Pseudo-cell a = 89' 41.2' T b O m (triclinic) TbOl.780 Tb01.713 (rhombohedral) Tb01.800 Pseudo-cell Triclinic a = b = c = 5.286 f 0.001 A. (I = 8 , = 89' 25' y = 90' T b 0 i . m Pseudo-cell Rhombohedral a = 5.283 f 0.001 A. (I = 89" 41' TbOi.96 Face centered cubic a = 5.220 0.001 A.
studies. Temperatures in excess of 1 1 0 0 O probably would be required to obtain rapid equilibrium and then an enormous oxygen pressure would be needed to observe the higher oxides. Symbols same as in Table 11. Figure 1 shows the interrelation of the phases " ~ ~the ~~ been observed in the terbium-oxygen system. found in the terbium, p r a s e o d y m i ~ r n ~and '~ Although this may They are Tb01.500, Tb01.715, Tb01.81, Tb01.83 and cerium 0 x i d e ~ ~ 8systems. TbOz.o. In addition, monoclinic B type Tb01.6 not show all the intermediate phases in the latter has been observed in a melted sample. The phases two systems, the appearance of the h 1 0 1 . 7 1 6 phase a t the extremes in composition have structures of in all three is striking. It has been deterrnined15 high symmetry, the intermediate phases show lower that the Pr01.715 phase is isostructural with TbOl.716. symmetry with the least symmetrical phase hav- It is also notable that a MO1.78 phase has been obing the composition TbO1.81 Miscibility gaps served in the praseodymium and cerium-oxygen are observed in the lower composition range and are (12) R . E. Ferguson, E. D. G u t h a n d L. Eyring, J . A m . Chem. SOG.. 76, 3890 (19.54). implied a t higher compositions. G. Brauer and H.Gradinger, Z. anorg. u. allgem. Chem., 277, I t should be understood that the terbium-oxygen 89(13) (1954). system is quite sluggish, and hence true equilibrium (14) D. J. M . Bevan, J . I n o r g . Nuclear Chem., 1, 49 (1955). probably has not often been achieved in these (15) Unpublished work. I*
,42547 .43131 ,57326 ,67441
w m m
May 20, 1961
C H E L A T E STABILITY OF 4-HYDROXYBEXZOTHIAZOLES
systems. (This rhombohedral phase probably has the formula M9016, as suggested by the possible values in Table V.) A MOl,sl phase occurs in the terbium and cerium oxygen systems, and a phase is found in the terbium and praseodymium systems. The latter phases are not isostructural. The Tb01.83phase has a rhombohedral cell and the Pr01.83has a face-centered-cubic unit cell. Whether or not there are miscibility gaps between the various phases or homogeneous ranges of composition depends primarily upon the temperature and the oxygen pressure. A notable omission is a stable M407 phase in any of the three systems. This phase frequently has been reported for the terbium and cerium systems, but the studies reported and summarized have not given any evidence of special significance for such a stable solid phase. An important group of mixed oxides of formula M407 recently have been described and named for the mineral Pyrochlore. I 6 , l 7 Many studies have been made during the last decade18-20on mixed oxide phases of fluorite type with oxygen vacancies. It is not at present clear how the truly binary oxides discussed above compare with the pseudo binary mixed oxides. It will be important to know if the mixed oxides reported as solid solutions of the fluorite type are really that or if, when properly annealed, they show a tendency toward ordering of oxygen vacancies as demonstrated in the true binary oxide phases reported here. In this respect, i t will be necessary to carry out the studies a t temperatures where cation mobility is appreciable. Cation mobility is not required in the truly binary systems since electron movement will accomplish the same effect. (16) R. S. Roth, J. Research &‘at!. Bur. Standards, 56, 17 (1956), Res. Paper No. 2643. (17) A. J. E. Welch, private communication. (18) J. D. McCullough, J. A m . Chem. Sac., 74, 1386-1390 (1950). (19) J. D. McCullough and T. D. Britton, ibid.,74, 5225 (1952). (20) G. Brauer and H. Gradinger, 2. anorg. u . allgem. Chem., 276, 209 (1954).
[CONTRIBUTION FROM THE
DEPARTMENT OF
2223
In all these systems, anion mobility is very high a t the temperatures a t which the experiments were carried out but cation mobility very low. It seems apparent that there are many ways of ordering vacancies in these materials and simple analogy will not be enough to be sure in any particular case. In some cases, the vacancies are reported as randomly I n these, it would be particularly important to study the electrical properties of the solids. It has been suggestedz4that the oxygen deficiency in structures such as these may result from the formation of surfaces of discontinuity by a shear mechanism. In this way, the oxygen loss would be accommodated without the appearance of vacancies, as such, in the lattice. Structures of this type already have been solved, for example, in the (Mo, W)n02n-l,25Tin02n-126and TiVOXz7systems. An alternative suggestion for the structure of bixbyite recently has been suggestedz8 in which the oxygen lattice is changed to give a rather more octohedral arrangement around the metal atoms without the vacancies previously proposed. This large set of anion defect structures related to the fluorite structure is a t once one of the simplest and yet most beautifully intricate systems. A detailed elaboration of them would go far in advancing an understanding of the relationship between ordered intermediate phases and nonstoichiometry in chemical compounds. (21) E. Zintl and U. Croatto, 2 . anorg. Chem., 292, 79 (1939). (22) U.Croatto and M. Bruno, “Proc. 11th Intern. Cong. Pure 8: Appl. Chem.,” Vol. I, 69 (1947). (23) J. S. Anderson, D. N. Eddington, L. E. J . Roberts and E. Wait, J. Chem. Sac., 3324 (1954). (24) A. D. Wadsley, J. and Proc. Roy. Sac. of N . S . W . , X C I I , 25 (1958). (25) C. Hagy and A. Magneli, Revs. of Pure Appl. Chem., 4, 235 (1954). (26) S. Andersson, Acta Chem. Scan., in press. (27) A. D. Wadsley, Acta Cryst., in press. (28) H. Dachs, Z. Krist., 107,370 (1956).
CHEMISTRY, UNIVERSITY O F
NOTREDAME,NOTREDAME,INDIANA]
Chelate Stabilities of Certain Oxine-type Compounds. II. 4-Hydroxybenzothia~oles~ BY T. J. LANE,C.S.C.,
AND
A. SAM
RECEIVED NOVEMBER 5 , 1960 The acid dissociation constants of 4-hydroxybenzothiazole, 2-amino-4-hydroxybenzothiazole, 2-methylamino-4-hydroxywere determined in 50T0 v./v. p-dioxane a t 25’ and the chelate benzothiazole and 2-amino-4-hydroxy-7-methylbenzothiazole stability constants of the ligands with Cu(II), Pb(II), Ni(II), Co(II), Zn(I1) and Cd(I1) were obtained by Calvin-Bjerrum potentiometric titration technique. The results were compared with those previously reported for 8-hydroxyquinoline, 4hydroxybenzimidazole and 4-hydroxybenzoxazole. The stability constants of the 4-hydroxybenzothiazole chelates are This is explained by larger nitrogen-oxygen distance and by lower than those of the corresponding 8-hydroxyquinolinates. unfavorable electron orientation on the donor nitrogen atom. The stability values are higher than those of 4-hydroxybenzimidazoles and 4-hydroxybenzoxazoles and this is attributed to the influence of the larger sulfur atom in the I-position.
In the previous paper2 the chelate stabilities of 4-hydroxybenzimidazoles and of 4-hydroxybenzoxazoles with divalent ions have been reported. In the present paper are presented and discussed the values obtained for the metal chelates of the 4hydroxybenzothiazoles, represented by the (1) Presented a t the 138th Meeting of the American Chemical Society, New York, N. y.,1960. ( 2 ) T. J. Lane, A. Sam and A. J. Kandathil, J . A m . Chem. Sac., 84 4462 (1960).
formula
7‘
OH
R = H, “2, R’=H. CH3.
NHCH3
