COMPLEX IONS: PART 1 From left to right, aqueous solutions of: Co(NO3)2 (red); K2Cr2O7 (orange); K2CrO4 (yellow); NiCl2 (green); CuSO4 (blue); KMnO4 (purple).

Coordination Complexes CuSO4· 5H2O, [FeCl4] - ion and CrCl3·6 NH3, are called coordination complexes because they contain ions or molecules linked (or coordinated) to a transition metal. They are also known as complex ions because they are Lewis acid-base complexes. The ions or molecules that bind to transition-metal ions to form these complexes are called ligands (from Latin, "to tie or bind"). The number of ligands bound to the transition metal ion is called the coordination number

WRITING THE FORMULA Use brackets to enclose the ion [not always required] The metal is written first. The ligands follow, written in alphabetical order. The charge of the ion is written outside of the bracket.

METALS THAT FORM COMPLEXES mostly transition metals some main group elements also form complexes Aluminum, tin, and lead, for example, form complexes such as the [AlF6]3-, [SnCl4]2- and [PbI4]2- ions.

NAMING COMPLEX METAL IONS names of complex ions can look long and complicated the formulas are simply being coded in the same way that organic names are coded Once you have sorted out that code, the names are entirely descriptive.

thiocyanato (bonded – S) isothiocyanato (bonded – N) Naming the ligands ligand coded by (old name) H2O aqua aquo NH3 ammine ammino OH- hydroxo hydroxy Cl- chloro F- fluoro  CN- cyano  SCN- thiocyanato (bonded – S) isothiocyanato (bonded – N)

Take care with the code for ammonia as a ligand - it has 2 "m"s in its name. "amine" or "amino", refers to the NH2 group in an organic compound.

Coding for the number of ligands no of ligands coded by 2 di 3 tri 4 tetra 5 penta 6 hexa

Putting this together For a complex ion containing only one type of ligand, there is no problem. For example: [Cu(H2O)6]2+ is called the hexaaquacopper(II) ion. The fact that there are two "a"s next to each other in the name is OK. With more than one type of ligand in an ion, the ligands are named in alphabetical order - ignoring the prefixes. For example: [Cu(NH3)4(H2O)2]2+ is called the tetraamminediaquacopper(II) ion. The "ammine" is named before the "aqua" because "am" comes before "aq" in the alphabet. The "tetra" and "di" are ignored.

Naming the metal For positively charged complex ions A positively charged complex ion is called a cationic complex. A cation is a positively charged ion. The metal uses the English name with the addition of its oxidation state.

Naming the metal [Cu(H2O)6]2+ is called the hexaaquacopper(II) ion because the copper's oxidation state is +2. Copper's oxidation is +2 because the original uncomplexed ion was Cu2+ - NOT because the complex carries 2+ charges. The oxidation state is frequently left out if a metal has one oxidation state. For example, in its compounds aluminum always has an oxidation state of +3. [Al(H2O)6]3+ is usually just called the hexaaquaaluminium ion rather than the hexaaquaaluminium(III) ion.

Naming the metal For negatively charged complex ions A negatively charged complex ion is called an anionic complex. An anion is a negatively charged ion. In this case the name of the metal is modified to show that it has ended up in a negative ion. This is shown by the ending -ate. With many metals, the basic name of the metal is changed as well – the Latin root is used.

Naming the metal metal Changed to cobalt cobaltate aluminum aluminate chromium chromate vanadium vanadate copper cuprate iron ferrate lead plumbate sliver argentate

Suppose there are 4 chloride ions bonded around a Cu2+ ion to give [CuCl4]2-. The name shows the 4 (tetra) chlorines (chloro) around a copper in an overall negative ion (cuprate). The copper has on oxidation state of +2. This is the tetrachlorocuprate(II) ion and each Cl has a -1 charge, so overall charge of the ion is -2.

[Al(H2O)2(OH)4]- is called the diaquatetrahydroxoaluminate ion. Break the name into pieces so that you can see exactly what refers to what. Don't forget that the two different ligands are named in alphabetical order - aqua before hydroxo - ignoring the prefixes, di and tetra. The oxidation state of the aluminum could be shown, but isn't absolutely necessary because aluminum only has the one oxidation state in its compounds. The full name is the diaquatetrahydroxoaluminate(III) ion.

THE SHAPES OF COMPLEX METAL IONS These shapes are for complex ions formed using monodentate ligands - ligands which only form one bond to the central metal ion. Octahedral – coordination # = 6 Linear - coordination # = 2 Tetrahedral – coordination # = 4 Square planar – coordination # = 4

6-co-ordinated complex ions These are complex ions in which the central metal ion is forming six bonds to six ligands. These ions have an octahedral shape. Four of the ligands are in one plane, with the fifth one above the plane, and the sixth one below the plane.

4-co-ordinated complex ions These are far less common, and they can take up one of two different shapes. Tetrahedral ions [CuCl4]2- and [CoCl4]2-. The copper(II) and cobalt(II) ions have four chloride ions bonded to them rather than six, because the chloride ions are too big to fit any more around the central metal ion.

Tetrahedral ions

4-co-ordinated complex ions A square planar complex Occasionally a 4-co-ordinated complex turns out to be square planar. There's no easy way of predicting that this is going to happen. The only one you might possibly come across at this level is cisplatin which is used as an anti-cancer drug.

Cisplatin is a neutral complex, Pt(NH3)2Cl2 Cisplatin is a neutral complex, Pt(NH3)2Cl2. It is neutral because the 2+ charge of the original platinum(II) ion is exactly cancelled by the two negative charges supplied by the chloride ions.

Geometric isomerism

Geometric isomerism The two structures are isomers because there is no way that you can just twist one to turn it into the other. The complexes are both locked into their current forms. The terms cis and trans are used in the same way as they are in organic chemistry. Trans implies "opposite" or “across” - notice that the ammonias are arranged opposite each other in that version, and so are the chlorines. Cis implies "on the same side" - in this instance, that just means that the ammonias and the chlorines are adjacent to each other. Cis-trans isomerism occurs in octahedral and square planar complexes (but not tetrahedral).

WRITING EQUATIONS Excess ammonia is added to a solution of zinc nitrate. Zn2+ + NH3  [Zn(NH3)6]2+ 2005 AP Exam

WRITING EQUATIONS Excess hydrochloric acid is added to a solution of nickel(II) nitrate. NI2+ + Cl-  [NiCl4]2- 2006 AP test