The single crystal infrared spectrum and vibrational assignment of dichloroethylenediaminecopper (II)

CHEMICALPHYSICS4 (1974) 440-446.0

NORTH-HOLLANDPUBLISHINGCOMPANY

THE SINGLE CRYSTAL ASSIGNMENT

INFRARED

SPECTRUM AND VIBRATIONAL

OF DICHLOROETHYLENEDIECOPPER

(H)

G. PALIANI, R. CATALlO’TTland A. POLE-IT1 Istituto

di cilimica Fisica, Universitddi Perugia, 06100 Pwugia, Italy

and A.A.C. TOMLINSON CN.B. Laboratory /or Coordination Compounds. Istituto di Chimica Generale. Universirbdi Roma. 00100 Roma, Italy

Received 20 November 1973 The polarized infrared spectra of a single crystal of CuenC12 have been measured. A vibrational assignment is sug gestcd on the basis of group frequencies, polarization behaviour and application of the oriented gas model, where the latter is applicable, in addition lo isotopomer shifts of Cu(en-Nd4)Q2 and Raman spectra.

1. Introduction The vibrational spectra of ethylenediamine complexes of transition metal ions, especially those of Pd, Pt, Co, and Cr have been investigated by many workers [l-6]. Less attention has been paid to monoethylenediamine complexes [7], and that of copper (Jl), CuenC12, has not been investigated in depth. We have carried out an investigation of single crystals of this complex using polarised IR radiation, in order to refine the existing assignments for this type of complex and to see whether the oriented gas model is applicable.

2. Experimental CuenCl, was prepared as in the literature [8]. Suitsingle crystals could be obtained by slow growth from aqueous solution. All the crystals so obtained had well-developed (100) f;dces. in agreement with previous work [8,9]. Deuteration was carried out by recrystallisation from D20; three exchanges gave a deuteration of > 98% checked by usual IR method. This method allowed exchange of only the amine hydrogen atoms. The rapid exchange rate of the amine hydrogens frusable

trated efforts to obtain good spectra of deuterated single crystals. 1R spectra of very thin sections (polished with water) of the (100) face were recorded, between 4000250 cm-l, on a P.E. Model 521 spectrophotometer equipped with a gold wire grid polariser and R.I.I.C. beam condenser. Orientation of crystallographic axes with respect to morphology was found by X-ray methods, and agrees with previous work [9]. The spectra of the light and deuterated complexes were recorded between 4000-220 cm-’ as nujol mulls and KBr discs (there was no evidence of exchange of Cl- by Br-). Far IR spectra were recorded on a Beckmann IR 12 instrument, as nujol mulls between polyethylene plates.

3. Results and discussion Cuen$ crystallizes from water as monoclinic crystals of space group P2,, with two molecules in general positions in the unit cell. The most developed crystal plane is the (100) plane, which is also the cleavage plane. Each copper atom is coordinated to two chlorine atoms and two nitrogen atoms of the en

G. Paliani et al,

441

Single crystal IR spectrum and vibrational assignment oJC%enCl~

to form a square planar array. The plane of this square is parallel to the (010) face. The copper ion completes its very distorted pseudo-octahedral coordination by means of two chlorine atoms from adjacent molecules at very long distances (2.9 1 a) [8]. The structure analysis has shown that the atoms of the Cuen ring are not perfectly planar, one of the carbon atoms lying 0.5 A out of the plane of the ring. However, this deviation from planarity is so small that it may be ignored when discussing crystal spectra. The selection rules for the free molecule and for the modes of the unit cell are shown in table 1, where it is seen that each vibration of the free molecule should split into two modes in the crystal, both of which are IR and Raman active. Each band should thus split into two components. In addition, in the spectrum with polarised radiation incident on the crystallographic bc plane, with the electric vector pa-. rallel to b or to c, the intensities of these two components should be different depending on the orientation of the transition moment in the molecular reference system, and of the orientation of the latter with respect to the b and c axes. Table 2 shows the intensities, normalised along the crystallographic axes, of the two components of the factor group in the oriented gas model approximation. According to this model, with polarised light parallel to the (100) plane the following pattern of polarisation should be observed: I I molecular vibrations of Bt (i.p.) symmetry should be very intense when the electric vector is parallel to the b axis, 8 of B, symmetry should be very intense when the electric vector is parallel to c and 12 A, symmetry modes should be absent, or at least be very weak. Turning to the experimental spectra, there are 7

Table 1 Correlation diagram and selection rules Molecular group

Site group

Factor group

czv

Cl

c’z

Table 2 Proportionality factors for band intensity Crystal species

Isolated molecule L\.\is

Al

91

BL

A

b

0

B

c 11’

0.07 0.93

I 0 0

0 0.93 0.07

bands observed polarised along b, 5 bands polarised along c and some 12 bands appear withcut any appreciable polarisation (a typical spectrum of those between 1700-250 cm-* is shown in fig. I). Of the last mentioned, most have only low intensity, and thus are assigned to A, modes. The oriented gas model clearly fails in predicting the pattern of polarisation of these bands, this failure being, presumably, due to the mixing of vibrations in the unit cell. In fact, it is known that modes belonging to different irreducible representations of the molecular point group, but to the same representation of the factor group, may mix in the crystal field. A further reason for the failure of the oriented gas model, in the case of the above modes, may be traced, in our opinion, to the existence of the additional bonds between the copper and the chlorine atoms of adjacent molecules. Thus, the system may better be described as a long chain polymer rather than a collection of only weakly interacting free molecules. I I. Assignments The assignment reported in table 4 has been arrived at from both the polarisation behaviour and a comparison with the deuterated derivatives. Only those assignments leading to modification of previous ones on similar complexes will be discussed. 3.2. NH2 and CH, stretch& The NH, and CH2 stretching vibrations produce absorptions in the 3300-2800 cm-t region. Given that they are character&tic and well locaked group frequencies, their assignment presents little difficulty. in particular, we note the activation of the NT-T,stretthing vibrations of A, type due to the effect of &a crystal field. The experimentally obtained isotopic Shifts are in good agreement with theoretical ones pR-

G. Palianiet al., Single crystalIR specttum and vibmtional m.@nment of C&d72

442

Table 3 Wavenumbers and frequency ratio,of IR-acth

fundamental

modes in CnenC12 and CU(en-Nd&$ Cum-NWQ2

cud2

Single crya

KBr

dhc

IcBr disc

Polatisation

Wh

2476 3298

vs

3300

-

b

92

VY

1.34

2464 3250

I

3230

vs

236

vs

c

ms

110

b

b -c

A2

2430

w

1.34

BI

2384

vs

1.35

S

1.34

2330

3125 3116 2966

2318 s

2970

s

b

I

2938

s

C

2961

ms

2941

294s

Ins

9;

2936

2940 2884

2887 s

2872

s

b==c

ms

Al 2878

2819 157s

1570

1186

b-c

AI,&

w

b =-e

Al

s

C

91

vs

1562

1566

1467 mw

1476

1453

1457 m

1446

1448

1384 mw

1386

vs

132

1178 1467

m

1453 m

1448 1372 mw

b-c

mw

Al

1363

1358 mw

1361

mw

b

B2

1346

m

1305

mw

1308

m

b-c

81

1263

mw

1269

s

1270

s

b=c

Al

1027

mw

1.23

1128

a

1127

s

C

BI

916

us

1.23

1100

In

1102

m

C

A2

?

812

vs

1.35

1077

w

1076

m

c>b

Al

?

1086

w

1043

n

104s

ms

cab

Al

?

1052

vx

G. Pdhi

et al.. Singie

crystal

IR

spectrum

Table 3 (continued) Wavenumbers and frequency ratios of 1R-active fundamental

1017

ms

975

s

(887)’

ms

c

BI

978

ms

b

B?

885

VW mw

mw

876

682

vs

686 s

asnjpmf

modes in CUCII& and

1018

874

and vibmtiond

443

of ChtCf2

Cden*b)O2

1016

m

182 vs

1.25

A2

b>c

B2

868

m

b

B2

580

m

1.18

s

1.16

w

1.10

(626P

A2

533

vs

531

m

b

B2

460

480

m

476

w

b-c

Al

434

376

s

374

s

c

h

360

s

1.04

316

m

314

mw

b==c

Al

310

nl

1.02

284

w

281

w

265

m

258

m

221

s

193

w

.

BI

264 220

s

180 w (161)=

l

144

mw

124

s

104

w

88

m

Raman data 113).

dieted using Krimm’s rules 171. 3.3. NH2 and C.H2 deformations Spectra in the regions in which these modes occur

are very similar to those of PdenClz and PtenCla reported in ref. [7], and many have been assigned on this basis. However, examination of the polarisation behaviour, and the spectra of the deuterated derivative, introduces several modifications to the assign-

G. Paliani et a/., Single crystal IR specttum and vibmtional assignmeW of C%enC$

I

lo

I

(400

I

I *zoo

1

I

1000

I

I

I

I

800

I

I

600

400

CM-’

Fig. 1. Pohrised IR spectrum of the (100) face of CuenQ2 crystals. (-) ment of the twisting and wagging modes. The assignment of the two bands at 1353 and 1306 cm-’ has been inverted. On the basis of their symmetry, that at higher frequency is probably the CHI twist, of B, symmetry, and the other is the CH2 wag, of B, symmetry. The intense absorptions at 1269 and 1228 cm-! found at 1027 and 9 16 cm-l in the deuterated derivative (uH/uD = 1.23). belonging to species of symmetry A, and R, , respectively, are assigned to NH2 waggings [IO]. The two NH2 twisting modes are found at 1100 and 975 cm-t, respectively. The two CH, rocking modes occur at 887 and 874 cm-l, in agreement with earlier literature data [7, IO]. The first of these corresponds to a very weak absorption in IR, but strong in Raman*, and is attributed to an A2 symmetry mode. The NH* rocking modes absorb at 692 (580 cm-t in the deuterate, Y”/Y,, = 1.18) and 625 cm-‘, respcctively. The latter is observed only in Raman and is, consequently, assigned as of A, symmetry. l

The authors thank

Dr. T.R. Gilson

and for useful discussions.

for the Raman spectrum

& IIb. (---)

E IIc.

3.4. Ring modes The ring stretching modes (basically C-C and C-N stretchings) are attributed to the bands at 1077, 1043 (both of A1 species), and 1017 cm-l (of B, species). These absorptions remain more or less unaltered on deutetation. The ring deformations are found at 533, 480 and 284 cm-t. This assignment is in agreement with the powder data of Lever et al. [11,12]. 3.5. Cu-Nand

Ch-C7 vibrations

Following the above assignment criteria, and in agreement with Lever, we have assigned the Cu-N stretchings to bands at 376 cm-l (B1) and 316 cm-l (Al), and those of Cu-Cl to bands at 265 and 220 cm-l. The remaining bands between 200 and 80 cm-t are attributed to copper-halogen deformation vibrations and probably also to translational and librational lattice modes. The experimental data do not allow any clear conclusions to be drawn concerning this Dart of the spectrum,

G. Palianiet al.. Single crystalIR spectnrm and vibmtionalassignmentof CWnUz Table 4 Assignment

of fundamental

Symmetry

AI

A2

3

N

1

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39

vibrations

of CuenClz

and its Nd4 derivative

Description

NH2 stretch CHa stretch NH2 scissor CH2 scissor

CH2 wag NH2

445

wag

stretch Ring stretch Ring def. Cu-N stretch Cu-Cl stretch cuc12 scissor NH2 stretch CH2 stretch Ctis twist NH2 twist CH2 rock NH1 rock Ring def. CuCls twist NH2 stretch CHs stretch NH2 scissor CHa scissor CHa wag NH2 wag Ring stretch Cu-N stretch Ring def. Ring

Cu-Cl stretch CuCl~ rock

NH2 stretch CH2 stretch CH2 twist NH2 twist CH2 rock NH2 rock Ring def. CuCla wag

4. Conclusions The polarised IR spectrum of CuenC12 has allowed a reasonable assignment of the various bands to their symmetry species, via an application of the oriented gas model. Nevertheless, assignment becomes difficult for the 1200-950 cm-l region, where there are many

CuenCis

CuenC&

(cm-’ 1

(cm-’ )

3120 2883 1567 1467 1384 1269 1077 1043 480 316 265 -

2324 2831 1182 1467 1368 1027 1086 1052 434 310 264 -

3250

2430 -

- Nd,

1100 887 626

812

3230 2940 1567 1449 1305 1128 1017 376 284 221

2384 2943 1182 1450 1263 916 1016 360

3298 2966 1358 975 874 682 533

1470 2967 1346 782 868 580 460

220

absorption bands, presumably because of a high degree of mixing of the normal modes involved. This mixing is reflected in the polarization behaviour of many bands, thus complicating the interpretation for some. Further refinement of the assignment may be obtained only after recording spectra on other crystal faces, such as (010) and (001). To date we have not

446

G. Palianiet at.. Single crystel IR spectmn and vibmtianal assig-nmenrof CLenCt2

obtained sufficiently good crystals to be able to do this. However, polarised spectra of crystals tilted about both c and b axes by ca. 45”, gave results compatible with the assignments above. Thus, tilting about either b or c caused intensity enhancements of At symmetry modes, while the other symmetry modes remain more or less unchanged.

Acknowledgement

We thank Professor C. Pecile of Padua University for the use of the Beckmann far IR instrument.

References 111 D. Powelland N. Sheppard, J. Chem. Sot. (1959) 791.

I21 D. Powell and N. Sheppard, J.Chem. Sot. (1961) 1112. 131 D. Powell and N. Sheppard, Spectrochim. Acta 17 (1961) 68. 141 N. Tanaka, N. Sate and J. Fujita. Spectrochim. Acta 22 (1966) 57. IS] A. Eamshaw. L.F. Larkworthy and K.C. Patel, J. Chem. Sot. (1969) A 1339. [61 1. Nakagawa and T. Shimanouchi. Spcctrochim. Acla 22 (1966) 759. [7] RW. Berg and K. Rasmussex~,Spectrochim. Acta 29A (1973) 310. IS] G. Giuseppetti and F. Ma@ Rend. Sot. Mineral. Itab 11 (1955) 202. 191 D.E. Billing, RJ. Dudley, BJ. Hathaway, P. Nicholls and IY. Procter, J. Chcm. Sot. (1969) A 312. [lo] R.W. Berg and K. Rasmussen. Spectrochim. Acta 28A (1972) 2319. [ll] A.B.Pi Lever and E. Mantovani, Inorg. Chim. Acta 5 (1971) 429. [ 121 C.W. RaynerCanham and A.BP. Lever. Can. J. Chem. 50 (1972) 3866. (131 T.R. Cilson. private communication.