notes on nomenclature amine, etc; and (3) the order of ligands is alphabetical regardless of charge. The major problems which arise on the use of coordination nomenclature are these: (1) names for central atoms, (2) names for ligands, (3) indicating isomers, and (4) treating multicentered (polynuclear) compounds. The first two of these will be discussed in this note and others in subsequent notes. Names for Central Atoms
Abrlrwh Service Columbus, Ohio 43210
Chemicol
KURT LOENING ROY M. ADAMS
Geneva College Beover Poll% Pennsylvonio
15010
Normally the names in common use for the element are used both in cations, anions, and neutral, entities. However, there is a practice of long standing to use Latin names for the acids and anions of certain elements: argentate, aurate, cuprate, and ferrate. These are used in complex anions hut not in cations and neutral entities. Note, however, that hydrargyrate and stibonate are not in common use. Names for Ligands General
Coordination Nomenclature I. General Pattern The pattern of nomenclature known as coordination nomenclaturel is a distinctly inorganic contribution to nomenclature. Yet its simplicity and clarity are such that it is being used today in many areas quite outside that for which it was designed. Coordination compounds are considered to consist of a coordination center, most often a metal atom or ion (Co3+ below) to which are attached neutral (NH3) or anionic (CI-) groups called ligands 2+
In brief, cwrdination nomenclature is an additive scheme in which one names the ligands in the coordination entity (often called a complex), then the center to which the ligands are attached and finally in parentheses either (1) a Roman numeral (Stock number) indicating the oxidation state of the central or nuclear atom or (2) an Arabic number (Ewens-Bassett number) indicating the charge on the coordination entity. If the coordination entity is negatively charged, the cations paired with the complex anion (with -ate ending) are listed first; if the entity is positively charged, the anions paired with the complex cation are listed immediatelv afterward. [Co(NH.&CllCIz pentaamminechlorocobalt(nI) chloride pentaamminechloroeohalt(2+) chloride KJFefCN).COI -. . .potassium carbonylpentacyanoferrate(JI) potassium carbonylpentacyanoferrate(3-) Note these practices: (1) in formulas, the coordination entity is enclosed in hrackets; (because square brackets are reserved for enclosing the coordination entity, the nesting order for enclosing marks within the square bracketsbecomes: [( 11, [I( )I], [I[( )Ill, [Ill( )1I11, e t ~ . ) [NilP(OC&CH3)3131 tris(tr-o-tolyl phosphite)nickel(O) while, in (2) names there is no elision of vowels in penta-
Ligands may be classified in a number of ways: (1) charge, (2) multiplicity (number of points of attachment, occasionally called denticity) and (3) elements through which coordination takes place. Since the "a" ending already indicates a negative charge, there is no indication of the amount of charge on a ligand unless the parent suhstance can furnish more than one ligand which differ by the loss of a varying number of protons from the parent substance.
The use of Ewens-Bassett numbers as part of the ligand name requires the use of hrackets around the ligand names and multiplicative prefixes bis, tris, etc., rather than di, tri, etc. lMnlCsH4(0)(C00)l~(H10)rltetraaquobis[salicylato(2-)]manganate(m).
Ligands are classified on the basis of multiplicity (denticity) thus , unidentate2 one coordinatingatom (kultidentate
several cwrdinaKing atoms
The multiplicity of a ligand is usually characteristic for a given ligand. In case a ligand can coordinate in varying multiplicity, the particular ligand atoms through which attachment is effected are indicated by italicized symbols of the atoms involved following the ligand name.
~
468
/
Journal ot Chemical Education
'Complete details are available in the Red Book: "Nomenelature of Inorganic Chemistry, Definitive Rules 1970," (2nd Ed.) Butterworths, London, 1971, See. 7. Also published in Pure Appl. Chem., 28(1), 39(1971). ZMany are puzzled by the use of two different sets of numerical prefixes: uni-, bi-, ter-, and multi-dentate and mono-, di-, tri-, and poly-nuclear. Consistency dictates the use of the Latin prefixes with words of Latin origin: uni, bi, tri(ter), quadri, quinque, sexi, septi, octa; but the Greek prefixes with words of Greek origin: mono, di, tri, tetra, penta, hexa, hepta, octa. In practice, this distinction is not always maintained.
(-00CCH~)2NCH2CH2N(CH~COOo)2 eoordinated as a sexidentate ligand: lethylenediaminetetraaeetato(4-)I coordinated as a quinquedentate ligsnd: (ethylenediaminetetraacetato-O,Or,N,N',O"(4-)I
Such ligands have been called flexidentate. Whenever there is any question about the atoms through which the coordination takes place, they are designated by suffixing the italicized symbols of these atoms as above. This convention is particularly useful for ligands like SCN- which can coordinate through either of two elements Such ligands have been called amphidentate. M-SCN thiocyanatos M-NCS thiocyanato-N Anionic Ligands The names for anionic ligands end in -0 except that the customary radical names ending in -yl are used for hydrocarbon radicals. These are considered as possessing a negative charge in computing the oxidation number. In general, if the anion ends in -ide, -ite, or -ate, the final -e is replaced by -0, giving -ido, -it0 and -ato, respectively.
nium(ll1 Na[B(NOd+I sodium tetranitratoborate(1-) K[B(CeHs)rl potassium tetraphenylborate(II1) (Note that a two-word name for a ligand remains two words in the composite name.) Enclosing marks are required for inorganic anionic ligands containing numerical prefixes, as (triphosphato), for thio, seleno, and telluro analogs of 0x0 anions containing more than one atom, as (thiosulfato), and for organic ligands except hydrocarbon radicals. potassium (diiulfid
