Documents\Palladium-contents. Pdf

EHC 226: Palladium
Table 1
(contd).
Chemical
name
Synonyms
Molecular formula
CAS registry
no.
16
Palladium(II)
iodide
Palladous iodide
PdI
2
7790-38-7
Palladium(II)
nitrate
Palladous nitrate
Pd(NO
3
)
2
10102-05-3
Palladium(II)
oxide
Palladium
monoxide
PdO
1314-08-5
Palladium(II)
sulfate
Palladous sulfate
PdSO
4
13566-03-5
Potassium
hexachloro-
palladate(IV)
K
2
PdCl
6
16919-73-6
Potassium
tetrachloro-
palladate(II)
Potassium
palladium chloride
K
2
PdCl
4
10025-98-6
Sodium
tetrachloro-
palladate(II)
Na
2
PdCl
4
@
3H
2
O
13820-53-6
Tetraammine
palladium(II)
chloride
Tetraammine
palladium(II)
dichloride
[Pd(NH
3
)
4
]Cl
2
13815-17-3
Tetraammine
palladium
hydrogen
carbonate
TPdHC
Tetramminepalladiu
m hydrogen
carbonate
[Pd(NH
3
)
4
](HCO
3
)
2
134620-00-1
Tetrakis(tri-
phenyl-
phosphine)
palladium(0)
Pd[(C
6
H
5
)
3
P]
4
14221-01-3
a
 
Compiled  from  Degussa  (1995);   Aldrich  (1996);   Kroschwitz  (1996); Lovell,
personal communication, Johnson Matthey plc, August 1999.
compounds,  palladium  most  commonly  exhibits  an oxidation state of
+
2.  Compounds  of  palladium(IV)  are  fewer  and  less stable. Like the
other  PGMs,  palladium  has  a  strong  disposition  to  form coordination
complexes.  The  complexes  are  predominantly  square  planar  in  form.  In
addition, palladium forms a series of organic complexes, reviewed in
Kroschwitz (1996). The organometallic palladium(II) compounds
include 
F
-bound alkyls, aryls, acyls and acetylides as well as 
B
-bound
(di)olefins, alkyls and cyclopentadienyls.

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Identity, Physical and Chemical Properties, Analytical Methods
17
Table 2. Atomic and physical properties of palladium metal
a,b
 
Property
Palladium
Classification
Transition metal
Standard state
Solid
Specimen
Available as foil, granules, powder, rod,
shot, sponge or wire
Atomic number
46
Relative atomic mass 
106.42
Abundance of major natural
isotopes
c
105 (22.3%),106 (27.3%), 108 (26.5%)
Colour/form
Steel-white, ductile metal
Odour
Odourless
Electronegativity (Pauling
scale)
2.2
Crystal structure 
Cubic
Atomic radius (nm) 
0.179
Melting point (°C)
1554
Boiling point (°C)
2940
Exposure to heat or flame
Non-combustible; no decomposition
Density at 20 °C (g/cm
3
)
12.02
Reduction potential Pd/Pd
2+
of aqua complexes 
+0.92
d
 (at pH 1)
Solubility
e,f
Insoluble in water (pH 5–7), acetic acid
(99%), hydrofluoric acid (40%), sulfuric acid
(96%) or hydrochloric acid (36%) at room
temperature 
Slightly soluble in sulfuric acid (96%; 100
°C) and sodium hypochlorite solution (20
°C) 
Soluble in aqua regia (3:1 HCl/HNO
3
 at 20
°C) and nitric acid (65%; 20 °C)
a
 
Information valid for 
106
Pd unless otherwise noted. 
b
   Compiled from Smith et al. (1978); Lide (1992); Budavari et al. (1996).
c
 
103
Pd is not a naturally occurring isotope. 
d
 
Holleman & Wiberg (1995).
e
 
Degussa (1995).
f
For solubility in biological media, see section 6.1.
Physical  and  chemical  properties   of  selected palladium compounds
are given in Table 4.

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EHC 226: Palladium
18
Table 3. Examples of important palladium compounds by oxidation state
a
Oxidation
state 
Electronic
configuration
Examples
 Pd(0)
d10 
Pd, Pd[(C
6
H
5
)
3
P]
4
, Pd(PF
3
)
4
 Pd(II)
d8
[Pd(OH
2
)
4
]
2+
(aq), [Pd(NH
3
)
4
]
2+
, [Pd(NH
3
)
2
Cl
2
],
PdF
2
, PdCl
2
, etc., PdO, [PdCl
4
]
2–
, [PdSCN
4
]
2–
,
[PdCN
4
]
2–
, [Pd
2
Cl
6
]
2–
, salts, complexes
 Pd(IV)
d6
PdO
2
, PdF
4
, [PdCl
6
]
2–
a
 
Compiled from Cotton & Wilkinson (1982).
2.3
Analytical methods
Palladium  (as  a  solution  of  palladium(II)  nitrate  in  the  mg/litre
concentration  range)  is  frequently  used  as  a  chemical modifier to
overcome  interferences  with  the  determination  of  various  trace  ele-
ments  in  biological  materials  by  graphite  furnace  atomic  absor p t i o n
spectrometry (GF-AAS) (Schlemmer & Welz, 1986; Taylor et al., 1998).
Care  must  be  taken,  therefore,  in  analytical laboratories using palladium
chemical  modifiers  to  avoid  contamination  when  measuring  palladium
by the GF-AAS technique.
2.3.1
Sample collection and pretreatment
Palladium  is  rarely  found  in  significant  concentrations  in  any  kind
of  environmental  material. Environmental and biological materials being
investigated  for  very low levels of palladium need to be sampled in
large  amounts, with possible difficulty in homogenization, digestion,
s torage  and  matrix  effects.  In  order  to  obtain  enough  of  the  anal y t e   f o r
accurate  determinations  and  to  separate  the palladium from the sample
matrix and interfering elements, preconcentration is often necessary.
Several  chemical  methods for the separation and preconcentration
of  palladium  have  been  developed  —  for  example,  extracti o n   w i t h
various  agents,  separation  with  ion-exchange  resins,  co-precipitation
with tellurium or mercury and fire assay (Eller et al., 1989; Tripkovic et
al.,  1994). For example, palladium(II) in aqueous solution can be
extracted  by  diethyldithiocarbamate (Shah & Wai, 1985; Begerow et al.,
1997a),  N-p-methoxyphenyl-2-furylacrylohydroxamic acid (Abbasi,
1987)  or  1-decyl-N,N
N
-diphenylisothiouronium bromide (Jones et al.,
1977).

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