Nine-co-ordinate alkaline earth metals

J. inorg, nucl. Chem., 1967, Vol. 29, pp. 1427 to 1431. Pergamon Press Ltd. Printed in Northern Ireland

NINE-CO-ORDINATE ALKALINE EARTH METALS P. S. GENTILE, J. CAP,LOTTO and T. A. SHANKOFF Department of Chemistry, Fordham University, Bronx, New York 10458 (First received 30 June 1966; in revised form 14 November 1966)

Abstract--Ten diethylenetriamine (dien) complexes of Group HA salts were prepared. The perchlorates in the series, [Ca(dien)3](C104)z, [Sr(dien)a](CIO4)~ and [Ba(dien)3](ClO4)~ in addition to [Ca(dien)8](C103)2 were shown to be nine-co-ordinate as was the diacetamide complex [Ca(DA)4.d(C1Oa)v These conclusions were supported by i.r. data of transition metal dien complexes. In a similar manner the Group IIA halide-dien complexes, [Ca(dien)s]Br2, [Sr(dien)3]Br2, [Ba(dien)3]Br~, [Ca(dien)3]I2, [Sr(dien)a]I2 and [Ba(dien)dI~, have been postulated as having a co-ordination number of nine. The Bellamy-Williams equation was applied to the i.r. data. IN A FEW isolated instances (x-5) co-ordination numbers o f eight have been reported for G r o u p I I A metal salts with oxygen and nitrogen d o n o r ligands. Some indication o f higher ratios with ammines has been noted, c6) and inner hydration numbers o f eleven or greater have been indicated for calcium perchlorate (7) f r o m compressibility data. A recent investigation (s) o f alkaline earth metal salt complexes with diacetamide (DA) indicates that calcium and barium perchlorates f o r m nine-co-ordinated compounds, while the halides o f calcium, strontium and barium are postulated to be at least eight-, and possibly nine-co-ordinated. In order to obtain further evidence for nine-co-ordinate complexes, it seemed reasonable to use a terdentate ligand such as diethylenetriamine. This ligand was desirable for the following reasons: (1) evidence indicates that it co-ordinates in m o s t cases as a terdentate ligand; (2) it is structurally suited to co-ordinate as either a planar or vicinal species; c9) (3) transition metal complexes can be used as a basis for comparison in interpreting i.r. spectra. EXPERIMENTAL Materials and instruments All chemicals used were of the highest purity commercially available. Diethylenetriamine was distilled over sodium hydroxide pellets and the constant boiling fraction collected. Infra-red spectra were obtained using a dual grating Perkin-Elmer recording spectrophotometer No. 337. Flurorcarbon oil mulls were used. Analysis The alkaline earth metals and nickel were assayed by back titration to the Eriochrome Black-T end-point with EDTA. Cobalt and copper were precipitated as the sulphide, collected and destroyed with nitrous acid with subsequent titration to the murexide end-point with EDTA.

c1~A. Ggtm and J. HUSMANN,Ber. 43, 1291 (1910). ~ E. TASSILY,Ann. chem. Phys. 17, 48 (1899). ts~ H. RosE, Pogff. Ann. 20, 154 (1830). ~4~C. F. RAMM~LSBERa,Pogg. Ann. 55, 239 (1842). ts~ A. A. SCHILTand R. C. TAYLOR,J. inorg, nucL Chem. 9, 211 (1959). ~6)C. SMEErS,Natuurw. Tijdschr. 21, 149 (1939). ~) R. A. ROBINSONand R. H. STOKES,Electrolytic Solutions, p. 62. Butterworths, London (1959). c8) p. S. GENTILEand T. A. SrlANICOlW,J. inorg, nucL Chem. 27, 2301 (1965). ~*~ F. C. MANN, d. chem. Soc. 461 (1934). 1427

1428

P.S. GENTILE, J. CARLOTFOand T. A. SHANKOFF

Halides were determined argentiometrically using either dichlorofluoroscein or a titrimeter to detect the end-point. Diethylenetriamine was determined in the alkaline earth complexes by titration with 0.1000 N HCI to the chlorophenol red emi-point. Preparation and analysis Group IIA complexes. All these compounds were prepared by dissolving the metal salt (0-01 mole) in a suitable solvent such as ethanol, methanol or acetone, and adding an excess of a solution of the ligand or until evidence of reaction ceased. Ether was used to salt out the complex when precipitation did not occur immediately. The product was collected, washed with ether and dried in vacuo for 1 hr. [Ca(DA)4.5](C1Os)2. The hydrate, Ca(CIO3)~'2H20, was dissolved in a minimum amount of methanol and a 6 M excess of diacetamide was added. Ether was used to salt out the complex which was then washed with ether and dried in vacuo. Found: Ca, 5"95; N, 2"67. Calc. Ca, 6.05; N, 2.75. Transition metal complexes. Cobalt adducts were prepared and collected under nitrogen. [Co(dien)z]C12. A solution of 2-4 g of CoC12"6H20 in 30 ml of absolute ethanol was heated to 60° and a slight excess (0.5 ml) of a 25 ~ ethanol solution of diethylenetriamine was added. The salmonpink product was withdrawn from the reaction flask into a sintered glass funnel by suction and washed with an ethanol--ether solution (1 : 1), ether, and then dried in vacuo. In a similar manner [Co(dien)2](C10~)2"H20 was synthesized. [Ni(dien)~]Clv Two grams of NiCIa.6H20 were dissolved in 25 ml of absolute ethanol and the solution was added to a slight excess of diethylenetriamine in ethanol. The purple product was collected, washed and dried as described previously. The [2qi(dien)~](C104)8"H20 complex was prepared similarly. [Cu(dien)2]Clv A 25 Yodiethylenetriamine--ethanol solution was added dropwise to a hot solution of 1"7 g CuC12.2H~O in ethanol until a light blue precipitate formed. The complex was collected, washed and dried as described above. [Cu(dien)z](C10~)~.H20 was similarly prepared. The analytical results are shown in Table 1. TABLE 1.--ELEMENTALANALYSIS

Metal [Ca(dien)a](CIO~)~ [Sr(dien)3](C104)2 [Ba(dien)8](C104)2 [Ca(dien)3 ]Br~ [Sr(dienMBr~ [Ba(dien)8]Br~ [Ca(dien)s]Is [Sr(dien)a]I2 [Ba(dien)3]I~ [Ca(dien)a](CIOs)s [Co(dien)2]C12 [Ni(dien)z]Cla [Cu(dien)2]Cl2

Dien

Anion

Found

Calc.

Found

Calc.

7.20 14.22 21.11 7.72 15.39 22.31 6.70 13"03 19.63 7.69 17.40 17"31 19.32

7-31 14-70 21.27 7.87 15.73 22.64 6.64 13"46 19.60 7.76 17-53 17-40 18"64

55.46 52.23 47.90 60.60 55"24 51.04 51.19 47-54 44.29 59.68 21.14 20"64 21"59

56.43 51.93 47.93 60.76 55"57 51.02 51.30 47.55 44.18 59.93 21"09 21"11 20'81

Found

Cale.

31-56 28-44 26-11 41 "79 38"74 35"93

31"37 28.70 26"34 42"06 38"99 36.22

RESULTS AND DISCUSSION The nine-co-ordinate Group IIA complexes [Ca(DA)5](C104) 2 a n d [Ba(DA)5](C104) 2 were p r e v i o u s l y r e p o r t e d 3 s~ Because o f the large n u m b e r o f c a r b o n y l g r o u p s i n v o l v e d , t h e i.r. s p e c t r a were n o t u n e q u i v o c a l i n t h e d e f i n i t i o n o f o n e m o n o d e n t a t e d i a c e t a m i d e m o l e c u l e i n t h e p r e s e n c e o f f o u r b i d e n t a t e d i a c e t a m i d e molecules. H o w e v e r , i s o l a t i o n

Nine-co-ordinate alkaline earth metals

1429

of the present compound [Ca(DA)4.5](CIO3)s definitely substantiates the occurrence of nine-co-ordination for Group IIA metal salts. The interpretation of the i.r. spectrum in this case is unequivocal since all of the diacetamide molecules are in the trans-trans configuration and are clearly defined by a single sharp carbonyl absorption (1730 cm -1) and the occurrence of only the C-N-C asymmetric stretching mode (1236 cm-1) in the imide III region.

Group IIA dien complexes In view of the above it is not surprising that all the Group IIA salts form complexes in a 3:1 ligand-to-metal ratio with dien. Inspection of the i.r. data indicates that two sets of complexes have been formed. The spectra of the chlorate and perchlorate complexes, [Ca(dien)3] (CIO3)2,[Ca(dien)3](C104) 2, [Sr(dien)3](C104)2 and [Ba(dien)3](C1Oa)2, contain three bands in the N - H stretching region (3500-3100 cm-X), whereas those of the halides, [Ca(dien)z]Br z, [Sr(dien)3]Br 2, [Ba(dien)3]Br 2, [Ca(dien)3]I2, [Sr(dien)3]I~, [Ba(dien)3]I2 show five bands. Although i.r. spectra of dien complexes have not been interpreted in the past, one would presume that because of the nature of the two equivalently bound primary amines, two bands would arise from the asymmetric and symmetric N - H stretching modes, and one from the symmetric stretching N - H vibration of the bound secondary amine. This presumption is valid only if all three dien molecules in the complex encounter the same environment thus maintaining the equivalency of the amine groups. Since the chlorate and perchlorate complexes show three N - H absorptions, the above reasoning supports the contention that these compounds are nine-co-ordinate. The symmetric and asymmetric stretching modes of the primary amine were then assigned using the Bellamy-Williams equation ~1o)and are shown in Table 2. The excellent TABLE 2 . - - I . R . DATA FOR GROUP I I A AND TRANSITIONMETAL PERCHLORATE COMPLEXES OF DI-

E r m ~ E ~ a V a A ~ N E (cm -I)

NH2-Psrm [Ca(dien)a](CIO02 [Sr(dien)a](C1Ot)2 [Ba(dien)s](C104)2 [Ca(dien)3](C103)2 [Co(dien)~](CIO4)~.H20 [Ni(dien)d(C104)~.HaO [Cu(dien)~](C104)a'H~O

NI-Iz-vasym

Calc.

Found

NH-vBrm

3364vs 3360vs 3374vs 3355s 3351vs 3355vs 3379m 3349m

3292 3289 3301 3285 3281 3285 3305 3279

3293m 3290sh 3306m 3282sh 3279s 3284s 3295s 3263s

331ls 3304s 3318s 3301s 3301m 3306m 3310sh

agreement between experimental and calculated values further indicates that hydrogen bonding is not a serious consideration. The two additional bands appearing in the spectra of the halide set may be rationalized in a number of ways. One explanation is that the two bands may arise in an eight-co-ordinate compound if the unbound primary amine is not involved with hydrogen bonding or both hydrogens are equivalently bound. In either case the ~x0~ L. J. BELLAMY and R. L. WILLIAMS, Spectrochim.

Acta 9,

341 (1957).

1430

P.S. GENTILE,J. CARLOTrOand T. A. SrlANKOFF

Bellamy-WiUiams equation would apply. However, these two additional bands could also arise in a nine-co-ordinate compound if any of the six bound primary amines are non-equivalent in which case the Bellamy-Williams equation would not apply. The data in Table 3 show that the relationship does not hold and the argument TABLE3 . - - I . R .

DATA FOR GROUP

IIA AND TRANSriXONMETALHALIDECOMPLEXESOF DIETI-IYLENETRIAMINE(cm-1) NH~-vsym Found

NH2-vasym

Calc.

NH-vBv-m Unassigned

[Ca(dien)3]Brz

3344w

3274

3264s

3311vs

[Sr(dien)3]Br2

3330w

3263

3250s

3294vs

[Ba(dien)3]Brz

3349w

3279

3259s

3309s

[Ca(dien)3]I~

3356w

3285

3271s

3317vs

[Sr(dien)8]I2

3346w

3277

3265s

3313vs

[Ba(dien)3]I,

3340w

3271

3262m

3313vs

[Co(dien)2]Clz

3317w

3251

3275s

3288sh

[Ni(dien)2]Cl2

3326w

3259

3264s

3284sh

[Cu(dien)dCl2

3344w 3321m

3275 3255

3270sh 3247m

3284sh

3224sh 3237s 3205s 3220s 3215s 3228s 3244sh 3256s 3225sh 3236s 3216sh 3227s 3178vs 3218s 3173vs 3222vs 3110sh 3152s 3184sh

in favour o f nine-co-ordination seems reasonable although, admittedly, other less plausible interpretations are possible. In addition there is not any a priori reason for assuming that the halides are eight-co-ordinate whereas the perchlorates are nineco-ordinate. Dien complexes of the transition metals Further evidence to support the arguments advanced above was obtained from dien complexes of the transition metals in which the co-ordination number could be definitely established from visible spectra. Several of the transition metal complexes obviously contain dien as a terdentate ligand and the electronic spectra of [Co(dien)~](C104)~.HaO (480, 515 (sh), 547 m/z) and [Ni(dien)z](C104)~.H~O (345, 534, 800 m/z, dearly define octahedral co-ordination in agreement with literature values. ~u'l~ Comparison of the i.r. data for these complexes with those o f the Group IIA chlorate and perchlorate adducts (see Table 2) reveals an excellent correlation between the number, position, and intensity of the bands in the N - H stretching region. Furthermore, it should be noted that [Cu(dien)a](C104)~.H20 which has been postulated to (it) p. PAOLETrI,M. OAMeOLIa~and L. SACCONI,J. chem. Soc. 3591 (1963). (1~)O. Bosaxtw and C. K. JORGENSEN,Acta chem. scand. U, 1224 (1957).

Nine-co-ordinate alkaline earth metals

1431

be five-co-ordinate~13'a~1 shows an i.r. spectrum which is decidedly different from the spectra of the other perchlorates. This would tend to confirm the view that any deviation of dien from normal terdentate co-ordination should be noticeable in the N-H stretching region. Finally, the visible data for the cobalt and nickel halide complexes indicate octahedral co-ordination and the i.r. data in the N-H region parallels that for the Group IIA halide complexes as shown in Table 3. The difference in the spectrum of [Cu(dien)2]Cl~ which is five-co-ordinate as compared to those of the other halides is not as definitive as in the case of the perchlorate. These spectra add further support to the conclusion previously reached that the Group IIA halide complexes are distorted by hydrogen bonding but are nonetheless nine-co-ordinated. It is unfortunate that the insolubility of these complexes in organic solvents and the inability of these species to survive in aqueous media preclude the possibility of obtaining further chemical data. Acknowledgement--We are grateful to the Atomic Energy Commission for their support under Contract No. AT(30-1)3675.

~ls}C. K. J¢ROENSEN,Acta chem. stand. 102, 900 (1965). ~x4~M. CIAMPOLLn, a, P. PAOLErnand L. SAccoNI,J. chem. Soc. 2998 (1961).