R A S U D ~DAS R SARMA
8934"
Vol. 78
of the whole molecule for a given normal mode of vibration (QA), may be expressed as13
Assignment.-The absorption bands observed a t 3600-3400 ern.-' and a t 1630-1600 ern-' are assigned, respectively, to the stretching and deformation vibrations of the water molecules present in the crystal.'' There is no doubt as to the assign1 ment of the bands in the 2100 cm.-l region t o the V = 5 Q~ZF~IL~XLIX various C=N stretching vibrations. According to our calculation made for the planar where (G-')iiLix2 and FiiLiiz are the distribution of Pt(CN)4' ion, we should observe in the absorption energies in the coordinate, Si, in a normal mode of vibration (Qh). The results of the calculation of spectra no other in-plane fundamental vibration to the region of 500 ctn.-' where the E, vithe potential energy distribution, FiiLii2, for each down bration (one of the metal to ligand vibrations) is normal mode of vibration, are shown in Table VI, expected to appear a t 319 ern.-'. This is nicely where figures in italics refer to the largest terms. shown by our experiment, the difference between In this way we determined the nature of each vibra- the computed value, 519 cm.-', and the observed tion more reasonably. value, 505 cm.-', being only 37,. One of the inplane deformation vibrations is expected to appear TABLE VI at 299 cm. - l and this is in complete agreement with THE POTENTIAL ENERGY DISTRIBUTION FiiLi2 FOR EACII our observation of an absorption band a t 300 cm.-l. h-ORMAL h f O D E O F \IIBRATIONa The other in-plane deformation vibration with the (AIS) J'I Vd calculated frequency of 80 cm.-l lies outside the S I 0.174 0.119 observable region. Therefore, the absorption peak SZ 2.594 ,008 observed a t 411 ern.-' is not an in-plane deforma(-4d Y 3 tion vibration. but one of the out-of-dane vibras3 0.036 tions (VIZ, ~13). (BI~) ~'4 v5 The determination of the metal to ligand freS4 0.033 0.0024 quencies has been a subject in which inorganic SS ,034 ,0024 chemists as well as molecular spectroscopists have (B2g) J'6 v7 been interested. As our results described above s6 0.168 0.116 are based on the experimental data of infrared abS7 2.594 ,008 sorption and the Raman effect as well as the normal v9 VI0 VI1 (E") va vibration calculation with a suitable force field, we Sa 0.176 0.149 0,000 0.000 can consider that our assignment of the metal to ,010 ,000 ,000 s 9 2.592 ligand frequency is very reasonable. Furthermore, SI0 0.000 ,000 ,017 ,0025 from the value of the force constant ICl, we can con,000 ,035 ,0012 ,000 s1I clude that the metal to ligand bond should be The values of force constants are given in the unit of IO5 fairly covalent in this cyanide complex. 0
dynes/cm. (13) I. Nakagawa, J Chrm. SOL.J a p a n , 74, 243 (1953); Y . Morino and K. Kutchitsu, J . C l z e ) n P h y s . , 20, 1809 (1952).
[COXTRIRUTIOS
(14) T h e weak bands a t 1630 and 1600 cm.-l of K C N are also due t o t h e trace of water present in t h e crystal. ?;OTRE
D A M E , ISDI.4S.4
FROM THE S O Y E S C H E M I C A L 1,ABORATORY O F T H E U S I V E R S I T Y O F I T
The Structure of Copper Monoglutamate B Y BASUDEBDAS
SARhI.4
RECEIVED L~CGUST 4, 1
(1)
O=C-CHCH2--CH?--C=O
I
0
\
\
SHa
,,'
/
I
FI
/
0
cu.--------o.----..~~.. cu
b H/
\
I
O==d'--CH2-CH2--CH-C=0
LIetal complexes with ghltalTIiC acid have been
described by various workers. The compounds with Cu(I1) were studied by Cheronis,2 hbderhalden,3Pfeiffer,' H ~ r r i g a and n ~ ~Rebertus.6b ( 2 ) 1;.n. Cheronis, U. S Patent 1,985,977 (Jan. 1, 1934). ( 5 ) E. Abderhalden a n d K. Kautzsch, Z. fihysioi. C h c n . , 64, 447 (1910); 68, 487 (1910); 78, 333 (1912). (4) P. Pfeiffer a n d H. Werner, i b i d . , 246, 212 (1937). ( 6 ) (a) P A . Horrigan, Thesis, University of Illinois, 1953, (b) R. r,. Rtll,ertiis, Thesis, University of Illinois, 1954.
THESTRUCTURE OF COPPERMONOGLUTAMATE
March 5 , 1956
893
the complex, and half of the copper is held in solution as the highly soluble sodium salt of copper bisglutamate which is stable under the circumstances. Rebertus found no evidence from polarographic data for the presence of two types of copper, one coordinated and the other ionic. Polarographic and spectroscopic data for copper monoglutamate and other a-amino acid complexes of copper show that in all probability the ligand is not tridentate to a single copper ion. Structure I1 requires a tetrahedral configuration around the copper, which is uncommon, and is improbable ig view of the strong absorption in the region 7000 A. where other, planar compounds of Cu-monoaminoacid complexes absorb most.6 Structures I11 and IV are proposed by Rebertus as alternatives. Copper monoglutamate, obtained as blue crystalline [CuG].2HzO, (sometimes as 2.5H20), loses 1.5 molecules of water a t 90-95" but the remaining half molecule cannot be removed without partial decomposition of the complex. This copper mono0 glutamate, on reaction with requisite amounts of barium hydroxide and glutamic acid, gives a barium salt that analyzes as Ba[CuGz]. The sodium salt, made in a similar way with sodium hydroxide and GH2, analyzes as the anhydrous compound. The sodium and barium salts are extremely soluble in water, while [CuG].0.5H20, formulated as Cu [CuGz].H20 by Pfeiffer, is very slightly soluble (0.0006 ,CH0 mole,&). The following scheme shows a number of THz \C=O /I \ I CH2 H 20 derivatives made from the copper monoglutamate complex. '\\ /O I -OOC-( CH?),-CH $: According to PfeifTer and Werner, copper mono?Cu-0-C=0 \2" *' "H20 glutamate (A) is to be formulated as Cu [CuGZ], and II?O,' so should show similarities to the barium, sodium, I11 I1 nickel and cobalt salts (B, C and D). Instead, -00C-( CH?),-CH-C=O however, there are some striking differences. ComI 1 pounds B, C and D are highly soluble in water and KHz 0 / are easily dehydrated a t go", whereas compound A cu 0 0 is very sparingly soluble and retains one molecule ,' \ 11 11 of water per two copper ions a t 95", even under H,O 0--C-(CH,)?-CH-C I 1 vacuum. The dimeric formula VI with a waterbridge between two copper ions, explains the retention of water and the reaction with ammonia to take up two molecules of ammonia in place of the ,,' \ one molecule of water. The low solubility would Is' H20 + also be expected on the basis of this structure. etc. The conductivity of a dilute solution (0.0003 M ) of O=C-CH-CH2--CH?-C=O [CuG].0.5H20 is very low compared to the conI / I ductivities of B, C and D. Infrared spectra of these compounds show a definite OH band for [CuG].O.5H20 a t about 2880 cm.-l, which indicates a strong bonding for the coordinated water. Absence of such a band in the spectra of the dehydrated B, C and D as well as in the spectrum of O=C-CH~-CH2-CH-C=0 [CuG.NH3]obtained from [CuG].0.5HzO supports v the view. Of these, the first was advanced by Pfeiffer and Experimental Werner on the basis of their observation that half CuGzCu] .3H20 (Compound A).-A solution of 8.5 g . of the total copper present is precipitated as hyH20 droxide when excess sodium hydroxide is added. (0.05 mole) of CuC12.2H20in 100 cc. of cold water was added They wrote the reaction Cu[CuG2] NaOH = slowly to a solution of 4 g. of sodium hydroxide and 7.5 g. Cu(0H)a Naz[CuGz] although they regarded the of /-glutamic acid. The solution was filtered immediately evidence as inconclusive. I n all probability a dras(6) W. C . Waggener, Am. Chem. Soc., 122nd m e e t i n g , A t l a n t i c C i t y , tic reaction with excess of strong alkali decomposes N. J . , S e p t e m b e r , 1952. Glutamic acid, HOOCCH2CH2CH"(2) COOH, here abbreviated as GH2, is especially interesting as a complexing agent, since it may behave as either a tri- or bidentate ligand. With copper i t gives two different types of compounds, in which the Cu :GH:, ratios are 1: 1 and 1:2, respectively. The latter was obtained as the sodium and the barium salts by Pfeiffer and Werner. Copper monoglutamate is the easier compound to obtain, since it forms over a wide range of Cu:glutamate ratios in the p H range 5-7.5. From potentiometric, polarographic, absorption, conductivity and magnetic data, Rebertus found that glutamic acid behaves as a tridentate ligand toward nickel(I1) and cadmium(I1) in their monoglutamato compounds. These complexes are ionic and supposedly tetrahedral. On the assumption that copper(I1) has a coordination number of 4, copper monoglutamate may be supposed to have one of the following structures.
1
r'
'\\
+
+
L
1
Ba(OH)2 Ba[CuGz]. ~ H z O of the dehydrated product. Calcd. for blue viol. cryst. B'i[CuG?]: CU, 12.89; C, 24.46; H , 2.83, f highly sol. in S,3 7 Yoitnrl: CU, 13 0;; C, 24.37; 11, : < . 0 4 , S,5 64. The anhr drous product was described by Pfeiffer . Preparation of CoGnCu (Compound D 1.A concentrated solution of BalCuGzl mas Cos04 filtd. mixed with a n equivalent quantiiy of cobalt [ CuG.NHs] CO[CUGZ] Ba[CuG,] wlfate dissolved in water. To the filtrate deep blue, sl. D, light blue viol, $- MeOH, B,blue ponder, highly was added a n equal volume of methanol, sol. sol. 9on vac sol. and the solution mas cooled arid filtered. The light blue-violet product was mashed SiSO4, filtd. with methanol and then with acetone, and MeOH, was dried a t 85" in zmczio. It w m readily 90" vac. soluble in water. Anal. Calcd. for [COGICU]: C, 25.09; 95O Ni[CuG,] H, 3.33; X, 6.65; Cu, 15.36. Found: h'a2[CuG2] SaZ[CuG2] .nH?O D, greenish blue, C, 28.47; H , 3.50; h-,6.42; Cu, 15.11. sol. in H?O C, blue powder, Preparation of KiCuG? (Compound D).-highly sol. This n a s made in exacilr the same WAV .I\ the cobalt compound. - A light greeGidiblue powder was obtained, fairly soluble in water. and allowed t o stand overnight a t room temperature. Blue rectangular prismatic crystals separated, were filtered by Anal. Calcd. for KiGzCu: C, 28.10; H , 3.33; K, suction, washed with water and finally with absolute alcohol 6.66; C u , 15.36. Fmlnd: c, 28.13; H, 3.97; N, 6.6ii; Cu, and dried in a vacuum desiccator. 1j.52. Anal. Calcd. for [C;?Zu].3H&: C, 24.64; H, A portion of the green nickel monoglutamate was treated in a solution of copper nitrate in water for 24 hours, during which time the upper part of it turned blue-the color of the 4.49; N, 5.72; Cu, 25.97. Found: C, 24.68; H , 4.53; copper monoglutamate. N, 5.65; Cu, 26.05. Infrared spectra were recorded with a Perkin-Elmer This product, prepared in a different way, was described by Lifschitz and S c h o ~ t e n d e r ,who ~ obtained the compositions spectrophotometer, Ifode1 21, using a sodiuni chloride crystal grating. Samples 1-11- w r e run in perfluoro-lube oil by [CuG2].2Hs0 and .2.5&0. The product was found to be du Pont, as Kujol blocked theregion where 0-H (str.) bands soluble t o the extent of 0.0005 mole/l. a t 25'. When dried at 90-95", it lost three molecules of water and then the are present in these compounds. A broad band at 2880 cm.-l in I indicates strongly coordinated xvatcr in the moleweight remained constant for 8-12 hours a t the same temcule. In order to clarify the point, compound I was prepared perature or a t 90" in vacuo. in the following way, where H20 mas replaced by D 2 0 . Anal. Calcd. for CuGzCu : C , 27.59; I T , 3 7; S, Barium copper bis-glutamate, Ba [CuGz] (0.039 g.), was H a dissolved in 1 cc. of heavy nater (90.87,)and mixed with a 6.45. Found: C,27.49; H , 4.01; S,6.54. solution of 0.016 g. of anhydrous copper sulfate in 1 cc. of heavy water. The mixture was stirred for 10 minutes antl This product was described previously by Pfeiffer and the precipitated barium sulfate filtered off. In about an Werner (dried at 100"). [Cu(NH3)Gz(NH,)Cu] .-A stream of carefully dried am- hour, blue crystals of copper monoglutamate separated. monia'gas, diluted with nitrogen, was passed over a sample They were filtered off and dried in vaczio a t 80" for an hour. The infrared spectrum of this compound in nujol shon-et1 a of CuGICu in a porcelain boat. In about half a n hour, strong band a t 2400 cm.-' compared to 2666-2784 cm.-' HzO reported in the literature for normal 0 - D (str.) vibration. the whole mass turned deep blue. The system was freed There is another hand a t 2435 ern.-' antl two s m d l shoulders from excess ammonia by a stream of nitrogen and heated to to the 2400 cm.-' band a t 2320 and 2350 crn.-'. T h e band 8 5 9 0 ' for 1-2 hours while vacuum was applied. The boat was then cooled in a vacuum desiccator over sulfuric acid. a t 2456 probably is t h e S-D hand due to some exchange of the h?.drogen on coBrdinated S H 2 . Further investigation T h e gain in weight was 3.8% compared t o the 3.91% calculated for the replacement of one molecule of water by two of the role of the nxtcr molrculc in the complex will be communicated Intcr. molecules of ammonia. h portion of copper monoglutamate, treated with nickel Anal. Calcd. for [CU(XHI)GZ(NHB)CU]:C, 26.66; nitrate in the same way, showed no change of color, indicatH, 4.44; N, 12.41. Found: C, 27.03; H, 4.60; X, 12.30. ing the copper compound to be much more stable than the nickel compound. Since the change occurred bodily in the Ba [CuG2].4H20.--8.7 grams of CuG Cu was ground solid state, the slightly lower solubility of the copper comHzb pound is expected to have no great effect. with 3.3 g . of Ba(OH)24H20 and 1.47 g. of I-glutamic acid Electrical resistance of copper glutamates (0.0005 .IT in a mortar and transferred into about 200 cc. of water. solutions, 2 5 " ) . The mixture was stirred for 4-8 hours and filtered. T o the deep blue solution, cooled in ice, was added 200 cc. of methCompmnil Resistancr anol in small portions, stirring it continuously. The deep 1 CuG.Cu 4.4t; x IO' blue product which separated was washed with methanol by decantation, dried at go", powdered, dissolved in a miniH i mum quantity of water and precipitated with methanol. 1.00 x 1 0 4 2 [CU(S€IB)G?(SHB)CL~] These operations were repeated two or three times. The 3 Co[CuG,I 0 . 3 3 x 10' blue powder was then dissolved in water and the solution 4 Ba[CuG?] 0 . 8 5 x 10: was concentrated at room temperature. The solid which separated was filtered with suction, washed with a little cold 5 Sa?[CuGI] 0 . 0 0 x 10' water, and was dried by suction for 5-6 days on the filter. The dry mass consisted of a mixture of a blue-violet crjsThe author expresses his deep gratitude t o Dr. talline product and a blue product, which were separated John C. Bailar, Jr., for his keen interest in this work, mechanically. I t was found that the violet product became and valuable suggestions. He is indebted to the blue on drying at 90-95'. Anal; Calcd. for BalCuG21.4H~O: C, 21.31; H , 3.91; University of Illinois and the National Science S, 4.9/. Found: C, 21.77; H, 4.37; N, 5.00. Anal. Foundation for financial help and to Mr. J. J. [CuG].2HzO blue rryst., sol.
90-95"
---+
[CuG].0.5H20 A, blue powder, snl.
1
iI
[
+
1
1
[
]
[
(i) I. 1,ifschitz and F. 1.. lf. S c h o u t e n d e r , R e r . t ) , i 7 ~chiin., . 5 8 , 41 1 (1939).
1
Brader for the infrared spectra. URBANA, ILLINOIS
