Chapter 20 Transition Metals and Coordination Chemistry

Chapter 20: Transition Metals and Coordination Chemistry 20.1 The Transition metals: A Survey 20.2 The First-Row Transition Metals 20.3 Coordination Compounds 20.4 Isomerism 20.5 Bonding in Complex Ions: The localized Electron Model 20.6 The Crystal Field Model 20.7 The Molecular Orbital Model 20.8 The Biological Importance of Coordination Complexes

Vanadium metal (center) and in solution as V 2+ (aq), V 3+ (aq), VO 2+ (aq), and VO 2 + (aq), (left to right).

Figure 20.1: Transition elements on the periodic table

Calcite with traces of Iron Source: Fundamental Photographs

Quartz

Wulfenite

Rhodochrosite

Aqueous solutions containing metal ions Co +2 Mn +2 Cr +3 Fe +3 Ni +2

Molecular model: The CO(NH 3 ) 6 3+ ion

Figure 20.2: plots of the first (red dots) and third (blue dots) ionization energies for the first-row transition metals

Figure 20.3: Atomic radii of the 3d, 4d, and 5d transition series.

Transition metals are often used to construct prosthetic devices, such as this hop joint replacement. Source: Science Photo Library

Liquid titanium(IV) chloride being added to water, forming a cloud of solid titanium oxide and hydrochloric acid.

Colors of Representative Compounds of the Period 4 Transition Metals b ac d e f g h i j a = Scandium oxide b = Titanium(IV) oxide c = Vanadyl sulfate dihydrate d = Sodium chromate e = Manganese(II) chloride tetrahydrate f = Potassium ferricyanide g = Cobalt(II) chloride hexahydrate h = Nickel(II) nitrate hexahydrate i = Copper(II) sulfate pentahydrate j = Zinc sulfate heptahydrate

Orbital Occupancy of the Period 4 Metals–I Element Partial Orbital Diagram Unpaired Electrons Sc 1 Ti 2 V 3 Cr 6 Mn 5 4s 3d 4p

Orbital Occupancy of the Period 4 Metals–II Element Partial Orbital Diagram Unpaired Electrons Fe 4 Co 3 Ni 2 Cu 1 Zn 0 4s 3d 4p

Oxidation States and d-Orbital Occupancy of the Period 4 Transition Metals 3B 4B 5B 6B 7B 8B 8B 8B 1B 2B Oxidation (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) State Sc Ti V Cr Mn Fe Co Ni Cu Zn (d 1 ) (d 2 ) (d 3 ) (d 5 ) (d 5 ) (d 6 ) (d 7 ) (d 8 ) (d 10 ) (d 10 ) (d 3 ) (d 5 ) (d 5 ) (d 7 ) (d 8 ) (d 10 ) (d 2 ) (d 3 ) (d 4 ) (d 5 ) (d 6 ) (d 7 ) (d 8 ) (d 9 ) (d 10 ) (d 0 ) (d 1 ) (d 2 ) (d 3 ) (d 4 ) (d 5 ) (d 6 ) (d 7 ) (d 8 ) (d 0 ) (d 1 ) (d 2 ) (d 3 ) (d 4 ) (d 5 ) (d 6 ) (d 0 ) (d 1 ) (d 2 ) (d 4 ) (d 0 ) (d 1 ) (d 2 ) (d 0 )

Figure 20.4: Titanium bicycle

Figure 20.5: Structures of the chromium (VI) anions

Manganese nodules on the sea floor Source: Visuals Unlimited

Aqueous solution containing the Ni 2 + ion

Alpine Pennycress Source: USDA photo This plant can thrive on soils contaminated with Zn and Cd, concentrating them in the stems, which can be harvested to obtain these elements.

Figure 20.6: Ligand arrangements for coordination numbers 2, 4, and 6

Figure 20.7: a) Bidentate ligand ethylene-diamine can bond to the metal ion through the lone pair on each nitrogen atom, thus forming two coordinate covalent bonds. B) Ammonia with one electron pair to bond. a) b)

Figure 20.8: The coordination of EDTA with a 2+ metal ion.

Rules for Naming Coordination Compounds - I 1)As with any ionic compound, the cation is named before the anion 2) In naming a complex ion, the ligands are named before the metal ion. 3) In naming ligands, an o is added to the root name of an anion. For example, the halides as ligands are called fluoro, chloro, bromo, and iodo; hydroxid is hydroxo; and cyanide is cyano. For a neutral the name of the molecule is used, with the exception of H 2 O, NH 3, CO, and NO, as illustrated in table ) The prefixes mono-, di-, tri-, tetra-, penta-, and hexa- are used to denote the number of simple ligands. The prefixes bis-, tris-, tetrakis-, and so on, are also used, especially for more complicated ligands or ones that already contain di-, tri-, and so on. 5) The oxidation state of the central metal ion is designated by a Roman numeral in parentheses.

Rules for Naming Coordination Compounds - II 6)When more than one type of ligand is present, ligands are named in alphabetical order. Prefixes do not affect the order. 7)If the complex ion has a negative charge, the suffix –ate is added to the name of the metal. Sometimes the Latin name is used to identify the metal (see table 20.15).

Example 20.1 (P 947) Give the systematic name for each of the following coordination compounds: a) [Co(NH 3 ) 5 Cl]Cl 2 b) K 3 Fe(CN) 6 c) [Fe(en) 2 (NO 2 ) 2 ] 2 SO 4 Solution: a)Ammonia molecules are neutral, Chloride is -1, so cobalt is +3 the name is therefore: pentaamminechlorocobalt(III) chloride b)3 K + ions, 6 CN - ions, therefore the Iron must have a charge of +3 the complex ion is: Fe(CN) 6 -3, the cyanide ligands are cyano, the latin name for Iron is ferrate, so the name is: potassium hexacyanoferrate(III) c) Four NO 2 -, one SO 4 -2, ethylenediamine is neutral so the iron is +3 the name is therefore: bis(ethylenediamine)dinitroiron(III) sulfate

An aqueous solution of [Co(NH 3 ) 5 Cl]Cl 2

Solid K 3 Fe(CN) 6

Figure 20.9: Classes of isomers

Structural Isomerism Coordination isomerism: the composition of the complex ion varies. consider: [Cr(NH 3 ) 5 SO 4 ]Br and [Cr(NH 3 ) 5 Br]SO 4 another example is: [Co(en) 3 ][Cr(ox) 3 ] and [Cr(en) 3 ][Co(ox) 3 ] ox represents the oxalate ion. Linkage isomerism: the composition of the complex ion is the, but the point of attachment of at least one of the ligands is different. [Co(NH 3 ) 4 (NO 2 )Cl]Cl Tetraamminechloronitrocobalt(III) chloride (yellow) [Co(NH 3 ) 4 (ONO)Cl]Cl Tetraamminechloronitritocobalt(III) chloride (red)

Figure 20.10: As a ligand, NO 2 - can bond to a metal ion (a) through a lone pair on the nitrogen atom (b) through a lone pair on one of the oxygen atoms

Figure 20.11: (a) The cis isomer of Pt(NH 3 ) 2 Cl 2 (yellow). (b) the trans isomer of Pt(NH 3 ) 2 Cl 2 (pale yellow). Cis - yellow Trans – pale yellow

Figure 20.12: (a) The trans isomer of [Co(NH 3 ) 4 Cl 2 ] 1. The chloride ligands are directly across from each other. (b) The cis isomer of [Co(NH 3 ) 4 Cl 2 ] 1.

Figure 20.13: Unpolarized light consists of waves vibrating in many different planes

Figure 20.14: Rotation of the plane of polarized light by an optically active substance.

Figure 20.15: human hand has a nonsuperimposed mirror image

Figure 20.15: human hand has a nonsuperimposed mirror image (cont’d)

Figure 20.16: Isomers I and II of Co(en) 3 3+ are mirror images (the mirror image of I is identical to II) that cannot be superimposed.

Figure 20.17: Trans isomer of Co(en) 2 Cl 2 + and its mirror image are identical(superimposable) (b) cis isomer of Co(en) 2 Cl 2 + No Optical activity Does have Optical activity

Figure 20.18: Some cis complexes of platinum and palladium that show significant antitumor activity.

Figure 20.19: Set of six d 2 sp 3 hybrid orbitals on CO 3 +

Figure 20.20: Hybrid orbitals required for tetrahedral square planar and linear Complexes

Figure 20.21: Octahedral arrangement and d-orbitals

Figure 20.22: Energies of the 3d orbitals for a metal ion in a octahedral complex.

Figure 20.23: possible electron arrangements in the split 3d orbitals of an octahedral complex of Co 3 +

Example 20.4 (P958) The Fe(CN) 6 -3 ion is known to have one unpaired electron. Does the CN - ligand produce a strong or weak field? Solution: Since the ligand is CN - and the overall complex ion charge is -3, the metal ion must be Fe +3, which has a 3d 5 electron configuration. The two possible arrangements of the five electrons in the d orbitals split by the octahedrally arranged ligands are: The strong-field case gives one unpaired electron, which agrees with the experimental observation. The CN - ion is a strong-field ligand toward the Fe +3 ion.

The Spectrochemical Series CN - > NO 2 - > en > NH 3 > H 2 O > OH - > F - > Cl - > Br - > I - Strong-field Weak-field ligands ligands (large ) (small ) The magnitude of for a given ligand increases as the charge on The metal ion increases.

Example 20.5 (P 959) Perdict the number of unpaired electrons in the complex ion [Cr(CN) 6 ] 4-. Solution: The net charge of 4- means that the metal ion must be Cr 2+ (-6+2=-4), which has a 3d 4 electron configuration. Since CN - is a strong-field ligand, the correct crystal field diagram for [Cr(CN) 6 ] 4- is The complex ion will have two unpared electrons. Note that the CN - ligand produces such a large splitting that two of the electrons will be Pared in the same orbital rather than force one electron up through the Large energy gap.

Figure 20.24: Visible spectrum

Figure 20.25: (a) when white light shines on a filter that absorbs wavelengths (b) because the complex ion

Figure 20.26: The complex ion Ti(H 2 O) 6 3+

Figure 20.27: Tetrahedral and octahedral arrangements of ligands shown inscribed in cubes.

Figure 20.28: Crystal field diagrams for octahedral and tetrahedral complexes

Figure 20.29: Crystal field diagram for a square planar complex oriented in the xy plane (b) crystal field diagram for a linear complex

Figure 20.30: Octahedral arrangement of ligands showing their lone pair orbitals

Figure 20.31: The MO energy- level diagram for an octahedral complex ion

Figure 20.32: MO energy-level diagram for CoF 6 3-, which yields the high-spin

Figure 20.33: The heme complex in which an Fe 2 + ion is coordinated to four nitrogen atoms of a planar porphyrin ligand.

Figure 20.35: Representation of the myoglobin molecule

Figure 20.36: Representation of the hemoglobin structure

Figure 20.37: Normal red blood cell (right) and a sickle cell, both magnified 18,000 times. Source: Visuals Unlimited

Hemoglobin and the Octahedral Complex in Heme

Figure 20.34: Chlorophyll is a porphyrin complex

The Tetrahedral Zn 2+ Complex in Carbonic Anhydrase