Intermolecular hydrogen bonding in crystals of (±)-methioninepalladium(II) chloride

INORG.

HUCL.

CHEM.

LETTERS

Vol.

3,

pp.

5S3-556, 1 9 6 7 . Pergamon Press

INTRWMOLECULARHYDROGENBONDING OF (±)_~TRIp~NEPAL~ADI~(II)

Ltd.

Printed

In

Great

IN CRYSTALS CHLORIDE

N.C. Stephenson School of Chemistry, University of New South Wales, Kensington, N.S.W., Australia J.F. McConnell and R. Warren School of Physics, University of New South Wales, Kensington, NsS.W., Australia (Recelv~ 19 5 ~ t ~ b e r T967)

In

a recent

oom~,nioation

spectra of PdCI2(MtH) reported.

1 details

of

the

infrared

[where MtH = methionine] were

These results were in agreement with the

structure proposed by Volshtein and Mogilevkina 2 on the basis of chemical behaviour and shown in fig. I.

The

carboxyl group is presumed not to be bonded to the central metal atom, but is free to participate in hydrogen bonding with, for example, the carboxyl group of a neighbouring molecule.

C--

H2

\

/ Cl Fig. I

~ C OOH x

P&

CHz

¢H3

Hydrogen bonding between carboxyl groups may be of two types, shown in fig. 2.

The first type leads to dimers,

for example with carboxylic acids, whereas the second type leads to a polymeric structure.

The infrared study of

McAullffe showed that the OH out-of-plane deformation 553

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551r

INTERMOLECULAR HYDROGEN BONDING

Yel 3, No. 12

appears as a narrow weak band for ¢he compound PdOI2(MtH ) in contrast to the intense broad peak of the carboxylic acid dimers.

On the basis of this and other differences

in spectral features between the palladium methionine complex and carboxylic acid dimers, and also the insolubility of the metal complex, it was suggested that in @he palladium(II)

and platinum(II)

complexes of methlonine the

hydrogen-bonding of the hydroxyl group does not result in a single planar system, but rather leads ~o a polymeric structure.

I

l

C

--C

\°~O--H-..O// Fig.

2(a)

i

0

0

C

,

o

I

0

I

2(b>

We have examined the crystel stwuc%~we of PdCI2(MtH) using single crystal, X-r~7 diffraction methods.

The unito cell is monoclinlc with a = 6.920, b = 13.788, c = 10.857 A

and ~ = 94.69 °.

There are four molecules per unit-cell and

the space group is P21/n.

Pifteen hundred data were

collee~ed using equi-inclination Weissenberg geometry and CoX= radiation.

Intensities were estimated visually and

internally correlated with d~ta collected about another axis. The structure was solved using Patterson and Fourier methods and refined by full matrix least-squares procedures.

The

residnal R at present has a value of O. 13 and the structure is depicted, in (100) projection,

in fig. 3.

Vol. 3, No. 12

INTERMOLECULAR HYDROGEN BONDING

555

, ~\,2'70

2?0 " \ \

,.,

131

1'58

7 /

/I

II /

231

The PdCI2(MtH)

molecules pack together as dimers and

the hydrogen-bondlng ylic acid dimers.

is similar to that occurring in carbox-

The two molecules in each dimer are

related by a centre of symmetry and the six atoms of the assooiated carboxyl groups are planar.

The length of the

O-H...O bond is 2.70~O.03 ~. The palladium atom lies 0.03 ~ out of the plane of its four bonded atoms, but nevertheless can be regarded as exhibiting approximately

square-planar

coordination.

The two

independent Pal-C1 distances (2.35 and 2.31 ~) are not signifIoantly different.

556

IHTERMOLECULAR HYDROGEN BONDING

Yol. 3, No. 12

Intramolecular bond distances within the coordinated methionine molecule are at present not k n o w n w i t h

sufficient

accuracy to enable a detailed comparison to be made between them and corresponding distances in the free molecule. 3

Reference s I.

C.A. McAULIFFE,

J. Chem. Soc

(A), 641 (1967).

2.

L.M. VOLSHTEIN and M.F. MOGILEVEINA,

Russ. J. Inorg.

Chem., 304 (~963). 3.

A. McL. MATHIESON,

Acta Cryst.,

332 (1952).