Chemistry Reference
In-Depth Information
Table 1.1
Typical concentrations (ppm) of selected metals ions in nature.
Metal
Earth's crust
Oceans
Plants (ryegrass)
Animals (human blood)
Na
23 000
10 500
1 000
2 000
K
21 000
1 620
28 000
1 600
Mg
23 000
1 200
2 500
40
Ca
41 000
390
12 500
60
Al
82 000
0.000 5
50
0.3
Sc
16
0.000 000 6
0.01
0.008
Ti
5 600
0.000 48
2.0
0.055
V
160
0.001
0.07
0.000 2
Cr
100
0.000 18
0.8
0.008
Mn
950
0.000 11
130
0.005
Fe
41 000
0.000 1
240
450
Co
20
0.000 001
0.6
0.01
Ni
80
0.000 1
6.5
0.03
Cu
50
0.000 08
9.0
1.0
Zn
75
0.000 05
31
7.0
Mo
1.5
0.01
1.1
0.001
Cd
0.11
0.000 001 1
0.07
0.0052
Pb
14
0.000 02
2.0
0.21
Sn
2.2
0.000 002 3
0.01
0.38
Ce
68
0.000 002
0.01
0.001
Keys to metal ion roles are their high charge (and surface charge density), capacity to
bind organic entities through strong coordinate bonds, and ability in many cases to vary
oxidation states. We shall return to look at metals in biological environments in more detail
in Chapter 8.
1.3.2
Metals in Contrived Environments
What defines chemistry over the past century has been our growing capacity to design
and construct molecules. The number of new molecules that have been synthesized now
number in the millions, and that number continues to grow at an astounding pace, along with
continuing growth in synthetic sophistication; we have reached the era of the 'designer'
molecule. Many of the new organic molecules prepared can bind to metal ions, or else can
be readily converted to other molecules that can do so. This, along with the diversity caused
by the capacity of a central metal ion to bind to a mixture of molecules at one time, means
that the number of potential metal complexes that are not natural species is essentially
infinite. Chemistry has altered irreversibly the composition of the world, if not the universe.
Discovering when the first synthetic metal complex was deliberately made and identified
is not as easy as one might expect, because so much time has passed since that event. One
popular candidate is
Prussian blue
, a cyanide complex of iron, developed as a commercial
artist's colour in the early eighteenth century. A more reliable candidate is what we now
know as hexaamminecobalt(III) chloride, discovered serendipitously by Tassaert in 1798,
which set under way a quest to interpret its unique properties, such as how separately
stable species NH
3
and CoCl
3
could produce another stable species CoCl
3
·
6NH
3
, and to
discover similar species. As new compounds evolved, it was at first sufficient to identify
them simply through their maker's name. Thus came into being species such as
Magnus's
green salt
(PtCl
2
·
2NH
3
). This first attempt at
nomenclature was doomed by profligacy, but as many compounds isolated were coloured,
2NH
3
) and
Erdmann's salt
(Co(NO
2
)
3
·
KNO
2
·
