ZEISE'S SALT - KPtCl3(C 2 H 4) Paper #3 November 18, 2014 ZEISE'S SALT - KPtCl3(C 2 H 4) Paper #3 November 18, 2014 ZEISE'S SALT - KPtCl3(C 2 H 4) This is the first metal complex identified as an organometallic compound KPtCl3(C 2 H 4) obtained from reaction of ethylene with platinum (II) chloride by William Zeise in 1825. It was not until much later (1951–1952) that the correct structure of Zeise's compound was reported in connection with the structure of a metallocene compound known as ferrocene. The anion of this air-stable, yellow, coordination complex contains an η2-ethylene ligand and features a platinum atom with a square planar geometry. Zeise's salt is of historical importance in the area of organometallic chemistry as one of the first examples of an alkene complex and that is the major reason for selecting this title. INTRODUCTION Inorganic chemistry is the study of the synthesis and behaviour of inorganic and organometallic compounds. This field covers all chemical compounds except the myriad organic compounds (carbon based compounds, usually containing C-H bonds), which are the subjects of organic chemistry. Organometallic compounds are considered to contain the M-C-H group. The metal (M) in these species can either be a main group element or a transition metal. Operationally, the definition of an organometallic compound is more relaxed to include also highly lipophilic complexes such as metal carbonyls and even metal alkoxides. In organometallic compounds, most p-electrons of transition metals conform to an empirical rule called the 18-electron rule. This rule assumes that the metal atom accepts from its ligands the number of electrons needed in order for it to attain the electronic configuration of the next noble gas. It assumes that the valence shells of the metal atom will contain 18 electrons. Thus, the sum of the number of d electrons plus the number of electrons supplied by the ligands will be 18. Ferrocene, for example, has 6 d electrons from Fe(II), plus 2 × 6 electrons from the two 5-membered rings, for a total of 18. Zeise's salt is a coordination compound, K+ ion and water molecule is present outside the coordination sphere. Both, the Cl-ion and ethylene are coordinated with Platinum ion, hence inside the coordination sphere. Molecular formula of the salt is given as K[PtCl3(C2H4)]·H2O ZEISE'S SALT PREPARATION W. C. Zeise, a professor at the University of Copenhagen was the first person to prepare zeise’s salt, he prepared this compound in 1820s while investigating the reaction of PtCl4 with boiling ethanol, and proposed that the resulting compound contained ethylene. in 1868 Birnbaum prepared the complex using ethylene. Zeise’s salt compound is now commercially available as a hydrate. Hydrates are inorganic salts "containing water molecules combined in a definite ratio as an integral part of the crystal that are either bound to a metal center or that have crystallized with the metal .

1. ZEISE'S SALT - KPtCl3(C 2 H 4) Paper #3
November 18, 2014
ZEISE'S SALT - KPtCl3(C 2 H 4) Paper #3
November 18, 2014
ZEISE'S SALT - KPtCl3(C 2 H 4)
This is the first metal complex identified as an organometallic
compound KPtCl3(C 2 H 4) obtained from reaction of ethylene
with platinum (II) chloride by William Zeise in 1825. It was not
until much later (1951–1952) that the correct structure of
Zeise's compound was reported in connection with the structure
of a metallocene compound known as ferrocene. The anion of
this air-stable, yellow, coordination complex contains an η2-
ethylene ligand and features a platinum atom with a square
planar geometry. Zeise's salt is of historical importance in the
area of organometallic chemistry as one of the first examples of
an alkene complex and that is the major reason for selecting this
title.
INTRODUCTION
Inorganic chemistry is the study of the synthesis and behaviour
of inorganic and organometallic compounds. This field covers
all chemical compounds except the myriad organic compounds
(carbon based compounds, usually containing C-H bonds),
which are the subjects of organic chemistry.
Organometallic compounds are considered to contain the M-C-H
group. The metal (M) in these species can either be a main
group element or a transition metal. Operationally, the
definition of an organometallic compound is more relaxed to

2. include also highly lipophilic complexes such as metal
carbonyls and even metal alkoxides.
In organometallic compounds, most p-electrons of transition
metals conform to an empirical rule called the 18-electron rule.
This rule assumes that the metal atom accepts from its ligands
the number of electrons needed in order for it to attain the
electronic configuration of the next noble gas. It assumes that
the valence shells of the metal atom will contain 18 electrons.
Thus, the sum of the number of d electrons plus the number of
electrons supplied by the ligands will be 18. Ferrocene, for
example, has 6 d electrons from Fe(II), plus 2 × 6 electrons
from the two 5-membered rings, for a total of 18.
Zeise's salt is a coordination compound, K+ ion and water
molecule is present outside the coordination sphere. Both, the
Cl-ion and ethylene are coordinated with Platinum ion, hence
inside the coordination sphere. Molecular formula of the salt is
given as K[PtCl3(C2H4)]·H2O
ZEISE'S SALT PREPARATION
W. C. Zeise, a professor at the University of Copenhagen was
the first person to prepare zeise’s salt, he prepared this
compound in 1820s while investigating the reaction of PtCl4
with boiling ethanol, and proposed that the resulting compound
contained ethylene. in 1868 Birnbaum prepared the complex
using ethylene. Zeise’s salt compound is now commercially
available as a hydrate. Hydrates are inorganic salts "containing
water molecules combined in a definite ratio as an integral part
of the crystal that are either bound to a metal center or that have
crystallized with the metal complex. Such hydrates are also said
to contain water of crystallization or water of hydration. If the
water is heavy water, where the hydrogen involved is the
isotope deuterium, then the term deuterate may be used in place
of hydrate. The hydrate is commonly prepared from K2[PtCl4]
and ethylene in the presence of a catalytic amount of SnCl2.
The water of hydration can be removed in vacuo.
ZEISE’S SALT PROPERTIES

3. EISE'S SALT CHEMICAL PROPERTIES
mp
220 °C (dec.) (lit.)
density
2.88 g/mL at 25 °C (lit.)
Molecular Formula:
C2H6Cl3KOPt
Formula Weight:
386.6
The first olefin complex of a platinum group metal to be
discovered was Zeise’s salt, K[C,H,PtCl,]. These olefin
complexes have, however,been the subject of intensive study
during the past decade (2, 3), with the result that not only are
large numbers of these compounds known but the structures of
many are alsounderstood and applications for them are now
being discovered.
In a homogeneous catalytic reaction where the net process is the
conversion of anolefin to some other species, the original
platinum metal salt or complex may be regarded as the catalyst
and the olefm-metal complex as the catalyst-substrate
combination.
There is much evidence to suggest that an olefin molecule co-
ordinated to a metal atom has a reactivity which is different in
kind from the normal reactivity of olefins. The act of co-
ordination decreases the electron density between the olefinic
carbon atoms, and hence renders the olefin liable to attack by
nucleophilic reagents such as hydroxyl or acetate ions, or
indeed any electron-rich species which is seeking an electron
deficient site. It is not possible to judge at the present how far
this hypothesis accounts for the reactions undergone by co-
ordinated olefins, although it almost certainly explains the
occurrence of oxidation and hydrogenation processes. study of
olefin oxidation, it was observed that if the reaction was
stopped before completion the olefin had isomerised and that an

4. equilibrium mixture of isomers was present .This led to the
discovery that palladous chloride and its olefin and nitrile
complexes catalysed olefin.ZEISE’S SALT STRUCTURE AND
CHARACTERIZATION
Zeise's salt K[PtC13. C2H4]. H20 forms monoclinic crystals, a
= 10.750_+ 0"006, b = 8.405 _+ 0-003, c 4.836+0-002 A, fl=
97-73 + 0.06 °, space group P21, with two formula units in the
unit cell.In Zeise's salt and related compounds, the alkene
rotates about the metal-alkene bond with a modest activation
energy. Analysis of the barrier heights indicates that the π-
bonding between most metals and the alkene is weaker than the
σ-bonding. In Zeise's anion, this rotational barrier cannot be
assessed by NMR spectroscopy because all four protons are
equivalent. Lower symmetry complexes of ethylene, e.g.
CpRh(C2H4)2, are, however, suitable for analysis of the
rotational barriers associated with the metal-ethylene bond. CC-
bond of ethylene in Zeise's salt still possesses double bond
character but to a lesser degree than free ethylene. This is
because the metal donates electrons to the antibonding p*-
orbital of the olefin thus reducing the bond order and
accordingly, the CC stretching frequency. With increasing
strength of the olefin-metal interaction, the metal-carbon bond
distance will decrease and the CC-bond distances will increase.
In zeise’s salt Pt(II) is the central metal ion which is a square
planar complex and the complex is diamagnetic. Central Pt 2+
ion coordinated with 3 Cl-ions and 1 ethene molecule in a
square planar geometry while the 4 coplanar H's are not
coplanar with the 2 C's. Pt—Cl (1) bond length is longer than
the Pt—Cl (2) and Pt—Cl (3) bond length. Which can be termed
as the trans effect is and is kinetically controlled. The intensity
of the trans effect (as measured by the increase in rate of
substitution of the trans ligand) follows this sequence: F−, H2O,
OH− < NH3< py < Cl− < Br− < I−, SCN−, NO2−, SC(NH2)2,
Ph− < SO32− < PR3, AsR3, SR2, CH3− < H−, NO, CO,
CN−,C2H4. This can be proved with X-Ray Crystallography,

5. and neutron diffraction. The bond stretching frequency for:C=C
is 1827 cm-1 (B.O.=2), C—C is 1650 cm-1(B.O.=1) and Ethene
present in the Zeise's salt 1738 cm1 (B.O.=1.54). the pi-acid
alkene donates electron density into a metal d-orbital from π-
symmetry bonding orbital between the carbon atoms (II). The
metal donates electrons back from (a different) filled d-orbital
into the empty π* anti bonding orbital (I).Both of these effects
tend to reduce the carbon-carbon bond order, leading to an
elongated C-C distance and a lowering its vibration frequency.
The coordination round the platinumatom is essentially square
planar. The deviations from the coordination plane (i. e. the best
plane throughthe platinum and three chlorine atoms) are Pt, + 0-
002;CI(1), 0.000; C1(2),o-0.015; CI(3), +0-005; centre ofC-C
bond, -0.15 A. The ethylene group is bound bya re-type bond to
the platinum atom, with the C-Cbond approximately
perpendicular to the coordinationplane• The deviations from
ideal symmetry are small,though significant: the C-C bond is
inclined at 86 ° to the coordination plane instead of 90 o, and its
mid-point is 0.15 A below the plane; in addition, C(1) is
displaced from the plane perpendicular to the coordination
plane and passing through Pt and CI(1), by 0.12 A. The Pt-C
distances are effectively equal, 2.15(2) A, and are rather longer
than 2.08 A, the distance predicted for a single Pt-C a-bond.
The C-C bond-length shows that coordination to the metal atom
reduces the bond-order in ethylene from 2 in the uncoordinated
molecule to about 1½ in this complex. Similar results were
obtained in the substituted acetylene complex [PtClz(ButC =
CBut) (ptoluidine)],where coordination reduces the C--C bond
order by about ½, and the Pt-C bond [2.19(2) A] is also longer
than expected for a single bond. It may be that olefins bond
more strongly to platinum than to palladium.
CONCLUSION
Two broad conclusions emerge from this research of platinum
metal salts as homogeneous catalysts. First, we sense the
enormous scope for the development of novel chemical

6. processes which is offered by the metalolefin system: there are
without doubt many more applications awaiting discovery and
exploitation. It is significant and important that homogeneous
catalytic processes are often more selective and specific than
the corresponding heterogeneous processes would be. Secondly,
there is a pattern of behaviour which may have implications in
wider fields. The types of complex formed depend in a way not
yet clearly formulated on the structure of the metal atom.
The reactivity of metal-olefin complexes has resemblances to
the reactivity of olefins adsorbed on metal surfaces. Thus it is
probably no coincidence that palladium salts feature largely as
homogeneous catalysts for reactions of olefms, while olefins are
known to be more weakly adsorbed by palladium than by
platinum.
.
REFERENCE
· American Chemical Society. (1962). Inorganic chemistry.
Washington, DC [etc.: American Chemical Society
· Shriver, D. F., Atkins, P. W., & Langford, C. H. (1990).
Inorganic chemistry. New York: Freeman
· Colomer, E. (1981). Inorganic chemistry. Berlin: Springer-
Verlag.