The Chapman & Hall/CRC Chemical Database is a structured database holding
information on chemical substances. It includes descriptive and numerical
data on chemical, physical and biological properties of compounds;
systematic and common names of compounds; literature references; structure
diagrams and their associated connection tables. Dictionary of Inorganic and
Organometallic Compounds (DIOC) Online is a subset of this and
includes all compounds contained in two of Chapman & Hall/CRC�s printed
chemical dictionaries, Dictionary of Inorganic Compounds (Main Work and
Supplements) and Dictionary of Organometallic Compounds (Second Edition
In general, DIOC includes the following compounds:
Binary and ternary compounds including hydrides, halides, oxides,
sulfides, selenides, tellurides, nitrides, phosphides, and some
Simple molecular compounds and their adducts, e.g. CS2, PF5.
Simple and complex oxides including heteropolyanions, e.g. SO3, BaO,
TiO2, La2O3, MgAl2O4, and representative silicates.
Common minerals, where possible included under the corresponding
'nearest pure substance'.
Important coordination compounds, e.g. amines, phosphines, alkoxy
complexes, and major well-characterised bioinorganics.
Organometallic compounds representative of all important structural types
(in the case of ligands with organic substituents, typically the parent
member of each series, where known, together with a selection of its
Compounds with an established use such as catalysts, starting materials,
synthetic reagents, etc.
Other compounds of particular chemical, structural, biological or historical
interest, especially those thought to exhibit unusual bonding characteristics.
Data presentation and organisation
Derivatives and variants
In the database, closely related compounds are grouped together to form an
entry. Stereoisomers and derivatives of a parent compound are all listed under
one entry. The compounds in the Dictionary of Inorganic and
Organometallic Compounds are grouped
together into approximately 60,000 entries. The structure of an entry is shown
Entry (parent compound)
Derivatives Variants (stereoisomers or other
Derivatives of the variant
In a simple entry, there is just one compound, with no derivatives or
variants. A composite entry will start with the entry name, then may have:
one or more derivatives at entry level
one or more variants of the entry
one or more derivatives of the variant
Variants are commonly stereoisomers or, in the case of intermetallic
compounds, substances having different stoichiometries.
Derivatives may include hydrates, complexes, salts, classic organic
derivatives and also the following special categories:
(a) Isotopically labelled compounds
Data on only the most important isotopic variants is included, generally
limited to those of hydrogen. Deuterium (2H) and tritium (3H) are denoted
separately in formulae as atoms D and T respectively and are alphabetically
indexed as for other atoms. Data for deuterium oxide (D2O), for example,
will be found within the entry for water.
Information on the most important isotopes for each element is provided
within the entry for that element.
(b) Dimeric and oligomeric substances
Where a compound is known in several states of aggregation, these are all
included in a single entry which usually refers to the monomer. The empirical
formulae of all the oligomeric forms are given as well as all appropriate
synonyms, and the compound can therefore readily be traced as the monomer
or the oligomer.
Compounds which are known only in dimeric form under normal
conditions are entered as such but the hypothetical monomers are included as
derivatives to provide the names and formulae of the monomeric forms.
(c) Anions and cations
Entries for ionic substances containing complex ions generally refer to the
naked complex cation or anion and the formula, formula weight and CAS
Registry Number given for the entry are those of the ion, in agreement with
current CAS practice. Salts of the ion with various counterions are then
treated as derivatives and the empirical formulae of the more important ones
If a specific salt is considered to be of particular importance, it will be
given an entry of its own, but there will be a cross-reference between the
entry for the complex ion and the salt. For example, the tetraphenylborates:
each salt is an important compound in its own right and there are thus
separate entries for sodium tetraphenylborate, potassium tetraphenylborate,
Wherever possible, minerals corresponding to synthetic compounds are
included within the entry for the synthetic compound, e.g. Zinc Blende and
Wurtzite are incorporated into the entry for Zinc Sulfide (ZnS). Only when a
mineral is the sole point of interest or unavailable synthetically is it given an
entry in its own right.
The format of a typical entry is given in Fig. 1, and shows the individual
types of data that may be present in an entry.
Chemical names and synonyms
All of the names discussed below can be searched using the Chemical
The Entry Name chosen to head each entry is that by which, in the opinion
of the editors, it is most likely to be known, and of use to, most users.
Systematic names following IUPAC conventions are used wherever
convenient, but trivial names may be used for more complex structures. In
cases where no one name stands out as being clearly more familiar or
convenient than others, the Chemical Abstracts name is normally used as the
An important function of DIOC is the provision of a wide range of
synonyms. In selecting the range of alternative names to present for each
compound or derivative, we have been guided by the following principles:
The function of the Dictionary is to report names which are found in the
literature, including Chemical Abstracts, and not to attempt to impose a
system of nomenclature. Therefore the editorial generation of new names has
been kept to the minimum required by consistency. The vast majority of
names given in DIOC are those given in the original paper(s) and in
In some cases, two or more non-identical compounds have been given the
same trivial name within the chemical literature. Where such a duplication
occurs, this is indicated by a dagger symbol (†) immediately following the
For compounds of complex structure, such as metal cluster derivatives,
only the CAS name is reported. Frequently, the authors of papers reporting
such compounds do not attempt to name them and it is to be assumed that
most users of DIOC wishing to locate such compounds will do so via the
There are many examples in the primary literature of the naming of
inorganic and organometallic compounds which is definitely incorrect
according to IUPAC convention, especially in the non-alphabetical ordering
of ligands in coordination compounds. Many of these incorrect forms are
Trivial variations in nomenclature which do not materially affect the
alphabetical ordering of the name are not included. Such minor variations are
legion: a common example is cyclopentadienyl complexes, which may be
named as η5-cyclopentadienyl, η-cyclopentadienyl (Royal Society of
Chemistry practice), η5-2,4-cyclopentadien-1-yl (current CAS practice),
π-cyclopentadienyl (8CI practice), or η5-cyclopentadienyl (older literature).
The spellings used for the elements Al, Cs and S in DIOC are aluminium,
caesium and sulfur respectively, as recommended by IUPAC.
CAS names. Names corresponding to those used by CAS during the 8th
through to the 12th Collective Index Periods (1967-71, 1972-76, 1977-81,
1982-86, 1987-1991 respectively) are labelled with the suffixes 8CI, 9CI,
10CI, 11CI and 12CI respectively. Names encountered in CAS since 1991 are
labelled 13CI although it is possible that some further changes may have
occurred before publication of the 13th Collective Index.
For the majority of inorganic compounds, and simple organometallic
compounds such as metal alkyls, the nomenclature brought in for the 9th
Collective Index Period (and referred to as 9CI nomenclature) has since been
unchanged. This is not true for some groups of compounds such as cluster
boranes and the more complex organometallic compounds, where the
nomenclature is still evolving. There are also many examples of the same
compound being registered more than once under different names (and
registry numbers) in CAS.
The following types of suffix which are to be found attached to CAS
names have been omitted. Firstly, stereochemical descriptors, e.g. in
Dicarbonyldichlorobis(triphenylphosphine)ruthenium the CAS descriptor
(OC-6-12) indicates the geometry shown below:
This is referred to in DIOC as the af-dicarbonyl-bd-dichloro-ce-diphosphine
form. Secondly, bonding descriptors, e.g. in
Hexa-μ-chlorohexachlorotriruthenate(4-) the CAS descriptor (2Ru-Ru)
denotes the presence of two ruthenium-ruthenium bonds. On the other hand,
oxidation state has in many cases been inserted in CAS names. See Section
Oxidation states and charges. For any given substance, the oxidation
state (also known as the Stock number) of the element of interest is
incorporated into at least one of the names given, using Roman numerals or
zero, provided that it can be unequivocally assigned. Oxidation states are
therefore generally omitted from nitrosyl complexes where the assignment of
oxidation state is often controversial, and also from compounds of elements
having only one common oxidation state, where it is unnecessary.
The overall ionic charge (also known as the Ewens-Bassett number) of a
complex is also provided in at least one name, using Arabic numerals.
CAS names do not describe oxidation states, only charges. However,
where the CAS name is the only readily accessible one, the oxidation state
has been added editorially. Where both oxidation state and charge occur in a
single name, the former precedes the latter.
CAS Registry Numbers
CAS Registry Numbers are identifying numbers allocated to each distinctly
definable chemical substance indexed by the Chemical Abstracts Service
since 1965 (plus retrospective allocation of numbers by CAS to compounds
from the sixth and seventh Collective Index Periods). The numbers have no
chemical significance but they provide a label for each substance independent
of any system of nomenclature.
Much effort has been expended to ensure that accurate CAS numbers are
given for as many substances as possible. If a CAS number is not given for a
particular compound, it may be (a) because CAS have not allocated one, (b)
very occasionally, because an editorial decision cannot be made as to the
correct number to cite, or (c) because the substance was added to the DIOC
database at a late stage in the compilation process, in which case the number
will probably be added to the database soon.
At the foot of the entry, immediately before the references, may be shown
additional registry numbers. These are numbers which have been recognised
by the Editors or contributors as belonging to the entry concerned but which
cannot be unequivocally assigned to any of the compounds covered by the
entry. Their main use will be in helping those who need to carry out
additional searches, especially online searches in the CAS or other databases,
and who will be able to obtain additional hits using these numbers. Clearly,
discretion is needed in their use for this purpose.
Additional registry numbers may arise for a variety of reasons:
A CAS number may refer to stereoisomers or other variants of the main
entry compound, e.g. bonding isomers, for which no physical properties or
useful information is available. In many cases, although CAS numbers are
allocated to different isomers, they are not assigned specifically to each one
and are merely labelled 'stereoisomers'.
Hydrates, salts, complexes, etc. which are not characterised fully.
A CAS number may refer to a mixture or to a particular
non-stoichiometric composition which is not detailed individually in the
Replaced numbers, duplicate numbers and other numbers arising from
CAS indexing procedure or, occasionally, from errors or inconsistencies by
CAS, are also reported.
Every attempt has been taken to achieve as much consistency and clarity in
the presentation of structural formulae as possible. The primary aim has been
to indicate the connectivity and, where known, the stereochemistry.
The diagrams are necessarily stylised and are intended to convey the
correct topochemistry rather than to convey accurate representations of bond
lengths and angles.
It is a general principle that abbreviations in structural formulae are kept to
a minimum and except for very common moieties (e.g. Ph) ligands are drawn
out in full.
It should be noted that in each entry display there is a single diagram
which applies to the parent entry. Separate diagrams are not given for
variants or derivatives.
Structures for derivatives can be viewed in Structure Search, but
remember that these structures are generated from connection tables and may
not always be oriented consistently.
Where no structure diagram is given for a particular entry, either the
structure of the compound is unknown or the user is referred to the diagram
of a related compound via the Structure by Analogy keyhole.
Bonding. The bonding in many transition metal complexes and clusters is
more or less complex and subject to varying interpretation, and is therefore
not amenable to accurate depiction by the conventions which serve
reasonably well for organic compounds.
Bridging hydrogens between two metal centres are depicted for clarity as
though there are full metal-metal bonds, although there is rarely so much
electron density between the two metals, e.g.:
Very considerable variations in conventions for depicting organometallic
compounds are to be found in the literature. For example, the two following
representations of the complex obtained from octacarbonyldicobalt and
acetylene refer to the same compound:
For sandwich complexes, the following convention, illustrated with
ferrocene as an example, is used throughout:
Boranes. BH groups in the cluster boranes and related species are
represented by vertices, as shown below:
Only when B is bonded to 2 (or more) non-bridging atoms is it depicted
explicitly. All other atoms, including carbon, are depicted explicitly.
This convention is analogous to the representation of CH2 or CH groups as
plain vertices in organic compounds and which is also used to depict ligands
in this database.
Polymeric transition metal complexes. Wherever possible, the
coordination polyhedron of the metal is depicted, and the points of
attachment to the next unit are indicated using bonds that extend outside
square brackets, e.g.:
Absolute and relative configurations are given according to the (R,S)- and
(E,Z)-conventions wherever feasible.
In the simplest case, the four substituent atoms about a tetrahedral carbon
atom are placed in order of increasing atomic number and the molecule is
then viewed from the side remote from the substituent of lowest priority. The
configuration is (R) (rectus) if the order of the three other groups from
highest to lowest is clockwise, and (S) (sinister) if it is anticlockwise.
Extensions of the (R,S)-system refer to situations such as axial and planar
Where only the relative configuration of a compound containing more than
one chiral centre is known, the symbols (R*) and (S*) are used, the lowestnumbered
chiral centre being arbitrarily assigned the symbol (R*). For
racemic modifications of compounds containing more than one chiral centre,
the symbols (RS) and (SR) are used, the lowest-numbered chiral centre being
arbitrarily assigned the symbol (RS).
For further information see Cahn, R.S. et al., J. Chem. Soc., 1951, 612;
Experientia, 1956, 12, 81; Angew. Chem., Int. Ed. Engl., 1966, 5, 383;
Prelog, V. et al, Angew. Chem., Int. Ed. Engl., 1982, 21, 567.
The use of the (R,S)-system for chiral polyhapto complexes is not covered
by the original Cahn-Ingold-Prelog rules and further specification of ligand
priorities and bonding convention is required.
Chiral metallocenes and related complexes.
The most widely employed
system for specification of metallocene chirality is due to Schlögl. The bond
from the central metal atom to the ring carbon atom under consideration is
treated as a formal single bond. The carbon atom is then considered as a
chiral centre and (R,S) nomenclature is applied in the usual way.
For further information see Schlögl, K., Topics in Stereochemistry, 1967,
39. In some older papers, the molecule is considered overall as a case of
planar chirality. However, this convention becomes ambiguous when applied
to some more complex structures.
Polyhapto ligand as a substituent on a chiral atom.
have been proposed for determining the order of priority of ligands where
one or more is π-bonded. Probably the one most widely accepted is due to
Stanley and Baird, in which the ligand is considered a pseudoatom of atomic
weight equal to the sum of all of the π-bonded atoms.
For further information see Stanley, K. et al, J. Am. Chem. Soc., 1975, 97,
This is an extension of the (R,S)-system for specifying configurations at
alkene double bonds. The substituents are ordered as in the (R,S)-system and
if the two of higher priority are on the same side of the double bond, the
configuration is (Z) (zusammen), while if they are on opposite sides it is (E)
Note that (E) does not always correspond to the trans- of the earlier
The various coordination polyhedra are depicted using wedged and dashed
bonds, the most common polyhedra being:
The shapes of polyhedra greater than 6 are not amenable to clear
representation by this means and a textual statement such as 'square
antiprismatic' is combined with the diagram.
The terms 'tetrahedral' and 'octahedral' are used in a general sense and do
not imply strict symmetry types. For the latter, the point group descriptors Td
and Oh are employed.
In the case of octahedral complexes bearing two different types of
substituents, the stereochemistry is adequately defined using the terms cis,
trans, fac or mer:
In more complicated cases, italised letters are used to designate the positions
of ligands in various configurations. The letters are assigned thus:
The first mentioned alphabetical ligand in the name is given the designator a,
the second ligand the next lowest designator and the assignments to the
remaining ligands then follow from this.
Stereochemistry for polydentate ligands is described using the α and β
The absolute configuration of certain octahedral complexes is described
using the Δ, Λ convention:
Molecular formula and molecular weight
The elements in the molecular formula are given according to the Hill
Convention (C, H and then other elements in alphabetical order). Each entry
is assigned a formula. This presents difficulties in the case of incompletely
characterised compounds. For such compounds the formula is shown in
square brackets to alert the reader to its artificiality. Examples include
complexes such as technetium citrate which are important commercially but
whose composition has not been determined. Artificial formulae are also used
in grouping together series of closely related binary compounds where it is
felt their organisation as a family is helpful to readers. For example, tungsten
silicides are grouped together in this way. The specific names and formulae
for different stoichiometries are all separately presented within the entry and
are fully searchable. Molecular formulae of important derivatives are
Molecular weights (or more strictly, molar masses in daltons) given are
computer calculated from the formulae using the values for atomic weights of
the elements published by the IUPAC Inorganic Chemistry Division,
Commission on Atomic Weights and Isotopic Abundances; Pure Appl.
Chem., 1991, 63, 975. Molecular weights are given to one decimal place, but
it is important to note that the atomic weights of some elements are variable
within wider limits than this implies. This applies not only to radioactive or
radiogenic elements such as Tc, U or Pb but also to some non-radioactive
elements, especially Li and B which exhibit a wider variation in
commercially available samples, and Pd which exhibits a wide natural
Care has been taken to make the information given on the importance and
uses of chemical substances as accurate as possible. Many substances have
now been patented for a wide variety of uses, but this does not imply that the
patented uses are of widespread applicability or even of established utility. In
general, information on the use of an inorganic or organometallic compound
is given when it has an established laboratory or industrial application or
where it has been shown to undergo or catalyse reactions of potential
usefulness. Data is this field may be searched under Use/Importance or All
Use of organometallic compounds as synthetic reagents is now widespread
and this is reflected in the addition of Synthetic Reagents Classification
Codes, which are searchable under the Type of Compound field.
Selected dimensions, usually obtained by x-ray crystallography, are provided:
bond lengths are given in picometres (pm = 10-12m = 10-2Å ) and angles in
This data describes whether a compound is solid, liquid or gas and also gives
an indication of its colour (even if colourless), crystal form and recrystallisation
solvent. Details of air, moisture and thermal stability are also
included where available.
Solubilities are quoted either qualitatively, e.g. Sol. THF; or quantitatively,
e.g. Sol. H2O (56g per 100cm3 at 25º).
Densities and refractive indexes
Densities and refractive indexes are now of less importance for the
identification of liquids than has been the case in the past, but they are quoted
for common or industrially important substances such as solvents, or where
no boiling point can be found in the literature.
Densities and refractive indexes are not quoted where the determination
appears to refer to an undefined mixture of stereoisomers.
Melting points and boiling points
These are quoted in degrees Celsius. The policy followed in the case of
conflicting melting point data is as follows:
Where the literature melting points are closely similar, only one figure
(the highest or most probable) is quoted.
Where two or more melting points are recorded and differ by several
degrees (the most likely explanation being that one sample was impure) the
lower figure is given in parentheses, thus: Mp 139° (135-136°).
Where quoted figures differ widely and some other explanation such as
polymorphism or incorrect identity seems the most likely explanation, both
figures are quoted without parentheses, thus: Mp 142°, Mp 205-206°.
Known cases of polymorphism or double melting point are noted. Many
organometallic compounds do not melt sharply due to decomposition at or
below the melting point and to difficulties of complete purification. There
are, therefore, numerous examples of wide discrepancies in melting point.
Boiling points are recorded at ambient pressure unless indicated by a
subscript representing the pressure in mmHg of the measurement, e.g. Bp10
140°. Boiling point determination is less precise than that of melting points
and conflicting boiling point data is not usually reported except when there
appears to be a serious discrepancy between the different authors.
Sublimation points are recorded in a similar style to boiling points, e.g.
These are given whenever possible, and normally refer to what the
contributor believes to be the best-characterised sample of highest chemical
and optical purity. Where available, an indication of the optical purity (op) or
enantiomeric excess (ee) of the sample measured now follows the specific
Specific rotations are dimensionless numbers and the degree sign which
was formerly universal in the literature has been discontinued.
pKa values are given for both acids and bases. The pKb of a base can be
obtained by subtracting its pKa from 14.7 (at 20°) or from 14.00 (at 25°).
Spectroscopic data such as ir maxima, uv wavelengths and extinction
coefficients are given in many cases where spectroscopic identification has
been important in characterisation, particularly for unstable compounds.
Efforts have been made, in particular, to include carbonyl and M-H
stretching frequencies wherever possible. In many other cases, spectroscopic
data can be rapidly located through the references quoted.
Limited thermodynamic data is provided. In many other cases, this
information can be located through the references quoted.
Hazard and toxicity information
Hazard and toxicity information is displayed in red type and additionally
highlighted by the sign .
The field of safety testing is a complex, difficult and rapidly expanding
one, and while as much care as possible has been taken to ensure the
accuracy of reported data, the Dictionary must not be considered a
comprehensive source on hazard data. The function of the reported hazard
data is to alert the user to possible hazards associated with the use of a
particular compound, but the absence of such data cannot be taken as an
indication of safety in use, and the publishers cannot be held responsible for
any inaccuracies in the reported information.
Many inorganic and organometallic compounds have not been evaluated
toxicologically but it is to be assumed that all compounds of certain elements
such as As, Be, Hg and Tl are toxic, and that compounds containing certain
groups such as perchlorate and azide are likely to be explosive.
The handling of the majority of air-sensitive inorganic and organometallic
compounds is to be regarded as hazardous to a greater or lesser degree
because of the risk of fire or explosion in contact with air. Not every such
sensitive compound has been specially marked as hazardous. Additionally,
many metal halides (often the starting point for organometallic synthesis) can
be easily hydrolysed, and all should be regarded as skin, eye and respiratory
RTECS®Accession Numbers *
Many entries in DIOC contain one or more RTECS® Accession Numbers.
Possession of these numbers allows users to locate toxicity information on
relevant substances from the NIOSH Registry of Toxic Effects of Chemical
Substances. The Registry is a compendium of toxicity data extracted from the
scientific literature and each substance is identified by a unique
nine-character alphanumeric RTECS® Accession Number.
For each Accession Number, the RTECS database provides the following
data where available: substance prime name and synonyms; update data;
CAS registry number; molecular weight and formula; reproductive,
tumorigenic and toxic dose data; citations to aquatic toxicity ratings, IARC
reviews, ACGIH Threshold Limit Values, toxicological reviews, existing
Federal standards, the NIOSH criteria document program for recommended
standards, the NIOSH current intelligence program, the NCI Carcinogenesis
Testing Program and the EPA Toxic Substances Control Act inventory. Each
data line and citation is referenced to the source from which the information
The selection of references is made with the aim of facilitating entry into the
literature for the user who wishes to locate more detailed information about a
particular compound. Thus, in general, recent references are preferred to
older ones. The number of references quoted cannot be taken as an indication
of the relative importance of a compound.
References are given in date order except for references to spectroscopic
library collections, which sort at the top of the list, and those to
hazard/toxicity sources which sort at the bottom.
The contents of many references are indicated by means of suffixes. A list
of the most common ones is given in Table 2.
Some reference suffixes are now given in boldface type, indicating where
the editors consider the reference to be particularly important, e.g. the best
synthesis giving full experimental details and often claiming a higher yield
than previously reported methods.
In some entries, minor items of information, particularly the physical
properties of derivatives, may arise from references not cited in the
Entry under review
The database is continually under updated.
When an entry is undergoing revision at the time of an on-line release (e.g. by addition of further derivatives or references),
this is indicated by a message at the head of the entry.
In general these are uniform with the Chemical Abstracts Service Source
Index (CASSI) listing except for a short list of very common journals:
Acta Cryst. (and sections thereof)
Acta Crystallogr. (and sections thereof)
Angew. Chem., Int Ed
Agnew. Chem., Ind. Ed. Engl.
Justus Liebigs Ann. Chem.
J. Chem. Soc., Chem. Commun.
J. Am. Chem. Soc.
J.C.S. (and various
J. Chem. Soc. (and various
J. Org. Chem.
Table 1. Abbreviations
Conference of Governmental Industrial Hygienists
National Standards Institute
(But for tert-butyl etc.)
gap (electron volts)
free energy of formation
enthalpy of formation
Ministry for Agriculture, Forestry and Fisheries
dose; LD50: a dose which is lethal to 50% of the animals
molecular mass (formula weight)
chemical vapour deposition
of refraction eg. (n20D for 20� and sodium
quadrupole resonance spectrum
of soln. acidity where pH = log10 (1/[H+]) where
[H+] is the hydrogen ion
of dissoc. const. (K) where pK = Log10(1/K)
(Pri for isopropyl)
magnetic moment (in Bohr magnetons μB)
States Adopted Name
Science Society of America
anion, usually halide
Table 2. Reference tags
The following is a selection of the most common reference tags that
config absolute configuration
13C nuclear magnetic resonance spectrum
X-ray crystal structure determination
electron paramagnetic (spin) resonance spectrum
high performance liquid chromatogrpahy
nuclear magnetic resonance spectrum
optical rotatory dispersion
proton (1H) nuclear magnetic resonance spectrum
properties (chemical or physical)
thin layer chromatography
ultra-violet visible spectrum
*RTECS® Accession Numbers are compiled and distributed by the
National Institute for Occupational Safety and Health Service of the
U.S. Department of Health and Human Services of the United States of
America. All rights reserved (1996).