Chapter 14 The Transition Elements and Their Chemistry Mn(VII) Cr(VI) V(V) Chapter 14 The Transition Elements and Their Chemistry

14.1 Properties of the Transition Elements 14.2 The Inner Transition Elements 14.3 Highlights of Selected Transition Metals 14.4 Coordination Compounds 14.5 Theoretical Basis for the Bonding and Properties of Complexes

The transition elements (d block) and inner transition elements (f block) in the periodic table.

The Period 4 transition metals

The Period 4 transition metals

The Period 4 transition metals

Orbital Occupancy of the Period 4 Transition Metals

Sample Problem 14.1 Writing Electron Configurations of Transition Metal Atoms and Ions PROBLEM: Write condensed electron configurations for the following: (a) Zr; (b) V3+; (c) Mo3+. (Assume that elements in higher periods behave like those in Period 4.) PLAN: The general configuration is [noble gas] ns2(n-1)dx. Recall that in ions the ns electrons are lost first. SOLUTION: (a) Zr is the second element in the 4d series: [Kr]5s24d2. (b) V is the thired element in the 3d series: [Ar]4s23d3. In forming V3+, three electrons are lost (two 4s and one 3d), so V3+ is a d2 ion: [Ar]3d10. (c) Mo lies below Cr in Group 6B(6), so we expect the same except in configuration as for Cr. Thus, Mo is [Kr]5s14d5. In forming the ion, Mo loses the one 5s and two of the 4d electrons to become a 4d3 ion: [Kr]4d3.

Horizontal trends in key atomic properties of the Period 4 elements.

Vertical trends in key properties within the transition elements

Aqueous oxoanions of transition elements. One of the most characteristic chemical properties of these elements is the occurrence of multiple oxidation states. Mn(II) Mn(VI) Mn(VII) V(V) Cr(VI) Mn(VII)

Oxidation states and d-orbital occupancy of the period 4 transition metals

Standard electrode potentials of period 4 M 2+ ions

Colors of representative compounds of the Period 4 transition metals. sodium chromate nickel(II) nitrate hexahydrate potassium ferricyanide zinc sulfate heptahydrate titanium oxide scandium oxide manganese(II) chloride tetrahydrate copper(II) sulfate pentahydrate vanadyl sulfate dihydrate cobalt(II) chloride hexahydrate

Some properties of group 6B(6) elements

There are 6 unpaired e- in Sm. Sample Problem 14.2 Finding the Number of Unpaired Electrons PROBLEM: The alloy SmCo5 forms a permanent magent because both samarium and cobalt have unpaired electrons. How many unpaired electrons are in the Sm atom (Z = 62)? PLAN: Write the condensed configuration of Sm and, using Hund’s rule and the aufbau principle, place electrons into a partial orbital diagram. SOLUTION: Sm is the eighth element after Xe. Two electrons go into the 6s sublevel and the remaining six electrons into the 4f (which fills before the 5d). Sm is [Xe]6s24f6 6s 4f 5d There are 6 unpaired e- in Sm.

The bright colors of chromium (VI) compounds.

Some oxidation states of manganese Orbital Occupancy *Most common states in bold face.

Steps in producing a black-and-white negative.

Components of a coordination compound. models wedge diagrams chemical formulas

Structures of Complex Ions: Coordination Numbers, Geometries, and Ligands Coordination Number - the number of ligand atoms that are bonded directly to the central metal ion. The coordination number is specific for a given metal ion in a particular oxidation state and compound. Geometry - the geometry (shape) of a complex ion depends on the coordination number and nature of the metal ion. Donor atoms per ligand - molecules and/or anions with one or more donor atoms that each donate a lone pair of electrons to the metal ion to form a covalent bond.

Coordination numbers and shapes of some complex ions

Some common ligands in coordination compounds

Names of some neutral and anionic ligands Names of some metal ions in complex anions

Formulas and Names of Coordination Compounds Rules for writing formulas: 1. The cation is written before the anion. 2. The charge of the cation(s) is balanced by the charge of the anion(s). 3. In the complex ion, neutral ligands are written before anionic ligands, and the formula for the whole ion is placed in brackets.

Formulas and Names of Coordination Compounds continued Rules for naming complexes: 1. The cation is named before the anion. 2. Within the complex ion, the ligands are named, in alphabetical order, before the metal ion. 3. Neutral ligands generally have the molecule name, but there are a few exceptions. Anionic ligands drop the -ide and add -o after the root name. 4. A numerical prefix indicates the number of ligands of a particular type. 5. The oxidation state of the central metal ion is given by a Roman numeral (in parentheses). 6. If the complex ion is an anion we drop the ending of the metal name and add -ate.

sodium hexafluoroaluminate Sample Problem 14.3 Writing Names and Formulas of Coordination Compounds PROBLEM: (a) What is the systematic name of Na3[AlF6]? (b) What is the systematic name of [Co(en)2Cl2]NO3? (c) What is the formula of tetraaminebromochloroplatinum(IV) chloride? (d) What is the formula of hexaaminecobalt(III) tetrachloro-ferrate(III)? PLAN: Use the rules presented - and . SOLUTION: (a) The complex ion is [AlF6]3-. Six (hexa-) fluorines (fluoro-) are the ligands - hexafluoro Aluminum is the central metal atom - aluminate Aluminum has only the +3 ion so we don’t need Roman numerals. sodium hexafluoroaluminate

dichlorobis(ethylenediamine)cobalt(III) nitrate Sample Problem 14.3 Writing Names and Formulas of Coordination Compounds continued (b) There are two ligands, chlorine and ethylenediamine - dichloro, bis(ethylenediamine) The complex is the cation and we have to use Roman numerals for the cobalt oxidation state since it has more than one - (III) The anion, nitrate, is named last. dichlorobis(ethylenediamine)cobalt(III) nitrate tetraaminebromochloroplatinum(IV) chloride (c) 4 NH3 Br- Cl- Pt4+ Cl- [Pt(NH3)4BrCl]Cl2 (d) hexaaminecobalt(III) tetrachloro-ferrate(III) 6 NH3 Co3+ 4 Cl- Fe3+ [Co(NH3)6][Cl4Fe]3

Some coordination compounds of cobalt studied by werner

Constitutional (structural) isomers Important types of isomerism in coordination compounds. ISOMERS Same chemical formula, but different properties Constitutional (structural) isomers Stereoisomers Atoms connected differently Different spatial arrangement Coordination isomers Ligand and counter-ion exchange Linkage isomers Different donor atom Geometric (cis-trans) isomers (diastereomers) Different arrangement around metal ion Optical isomers (enantiomers) Nonsuperimposable mirror images

Linkage isomers

Geometric (cis-trans) isomerism.

Optical isomerism in an octahedral complex ion.

Sample Problem 14.4 Determining the Type of Stereoisomerism PROBLEM: Draw all stereoisomers for each of the following and state the type of isomerism: (a) [Pt(NH3)2Br2] (b) [Cr(en)3]3+ (en = H2NCH2CH2NH2) PLAN: Determine the geometry around each metal ion and the nature of the ligands. Place the ligands in as many different positions as possible. Look for cis-trans and optical isomers. SOLUTION: (a) Pt(II) forms a square planar complex and there are two pair of monodentate ligands - NH3 and Br. These are geometric isomers; they are not optical isomers since they are superimposable on their mirror images. trans cis

Sample Problem 14.5 Determining the Type of Stereoisomerism continued (b) Ethylenediamine is a bidentate ligand. Cr3+ is hexacoordinated and will form an octahedral geometry. Since all of the ligands are identical, there will be no geometric isomerism possible. The mirror images are nonsuperimposable and are therefore optical isomers.

Hybrid orbitals and bonding in the octahedral [Cr(NH3)6]3+ ion.

Hybrid orbitals and bonding in the square planar [Ni(CN)4]2- ion.

Hybrid orbitals and bonding in the tetrahedral [Zn(OH)4]2- ion.

An artist’s wheel.

Relation between absorbed and observed colors

The five d-orbitals in an octahedral field of ligands.

Splitting of d-orbital energies by an octahedral field of ligands. D is the splitting energy

The effect of ligand on splitting energy.

The color of [Ti(H2O)6]3+.

Effects of the metal oxidation state and of ligand identity on color. [V(H2O)6]3+ [V(H2O)6]2+ [Cr(NH3)6]3+ [Cr(NH3)5Cl ]2+

The spectrochemical series. For a given ligand, the color depends on the oxidation state of the metal ion. For a given metal ion, the color depends on the ligand. I- < Cl- < F- < OH- < H2O < SCN- < NH3 < en < NO2- < CN- < CO WEAKER FIELD STRONGER FIELD LARGER D SMALLER D LONGER  SHORTER 

[Ti(CN)6]3- > [Ti(NH3)6]3+ > [Ti(H2O)6]3+ Sample Problem 14.6 Ranking Crystal Field Splitting Energies for Complex Ions of a Given Metal PROBLEM: Rank the ions [Ti(H2O)6]3+, [Ti(NH3)6]3+, and [Ti(CN)6]3- in terms of the relative value of D and of the energy of visible light absorbed. PLAN: The oxidation state of Ti is 3+ in all of the complexes so we are looking at the crystal field strength of the ligands. The stronger the ligand the greater the splitting and the higher the energy of the light absorbed. SOLUTION: The field strength according to is CN- > NH3 > H2O. So the relative values of D and energy of light absorbed will be [Ti(CN)6]3- > [Ti(NH3)6]3+ > [Ti(H2O)6]3+

High-spin and low-spin complex ions of Mn2+.

Orbital occupancy for high- and low-spin complexes of d4 through d7 metal ions. high spin: weak-field ligand low spin: strong-field ligand high spin: weak-field ligand low spin: strong-field ligand

Sample Problem 14.7 Identifying Complex Ions as High Spin or Low Spin PROBLEM: Iron (II) forms an essential complex in hemoglobin. For each of the two octahedral complex ions [Fe(H2O)6]2+ and [Fe(CN)6]4-, draw an orbital splitting diagram, predict the number of unpaired electrons, and identify the ion as low or high spin. PLAN: The electron configuration of Fe2+ gives us information that the iron has 6d electrons. The two ligands have field strengths shown in . Draw the orbital box diagrams, splitting the d orbitals into eg and t2g. Add the electrons noting that a weak-field ligand gives the maximum number of unpaired electrons and a high-spin complex and vice-versa. [Fe(CN)6]4- [Fe(H2O)6]2+ SOLUTION: potential energy 4 unpaired e-- (high spin) eg eg no unpaired e-- (low spin) t2g t2g

Splitting of d-orbital energies by a tetrahedral field and a square planar field of ligands.

Hemoglobin and the octahedral complex in heme.

Some transition metal trace elements in humans

The tetrahedral Zn2+ complex in carbonic anhydrase.