24 - 1 Transition Metals and Complexes Transition Metals Complexes and Coordination Compounds Stereoisomerism of Complexes Polydentate Ligands and Chelate

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Text of 24 - 1 Transition Metals and Complexes Transition Metals Complexes and Coordination Compounds...

  • Slide 1
  • 24 - 1 Transition Metals and Complexes Transition Metals Complexes and Coordination Compounds Stereoisomerism of Complexes Polydentate Ligands and Chelate Complexes Constitutional Isomerism in Complexes Nomenclature of Complexes d Orbitals Bonding in Complexes
  • Slide 2
  • 24 - 2 Transition metals Not as reactive as Group IA (1), IIA (2) metals and aluminum. d-block elements Except for palladium, all have either one or two s electrons in the outer shell. They only differ in the number of d electrons in n-1 energy level. Most have high melting and boiling points, high density, and are hard and strong. Multiple oxidation states are common.
  • Slide 3
  • 24 - 3 Changes in properties down groups In general, as you move down a group: The outer electron configurations are the same. Reactivity decreases. Comparing the three series. The second and third series are usually more like each other than like the elements of the first transition series. Example, zirconium and hafnium always occur together in nature but titanium does not.
  • Slide 4
  • 24 - 4 Changes in properties across periods Although the first period elements differ from the other two, properties vary in a similar manner as you move across a period. Lets look at several trends. Atomic radii Standard enthalpy of atomization Melting points Density Oxidation numbers.
  • Slide 5
  • 24 - 5 Atomic radii Radius, pm Group number Radii go through a minimum just after the center of each series. Periods 5 and 6 are near identical. Radii go through a minimum just after the center of each series. Periods 5 and 6 are near identical.
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  • 24 - 6 Standard enthalpy of atomization H HThis is the energy required to convert an element to individual gaseous atoms. M (s) M (g) at 25 o C and one atmosphere. A maximum is observed near the middle of each period. The same trend is found for melting point, boiling point and density. oa
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  • 24 - 7 Standard enthalpy of atomization H o a, kJ/mol Group number
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  • 24 - 8 Melting point, o C Group number
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  • 24 - 9 Density Density, g/cm 3 Group number
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  • 24 - 10 Transition metal trends Reason for trends. All show that attractions between atoms are strong. Strongest attractions are when the orbitals are half filled. Overlap of orbitals that contain one electron results in a covalent bond between atoms. Since metals at either end of a period have the fewest unpaired electrons, bonding is not as strong.
  • Slide 11
  • 24 - 11 Oxidation states. The number of oxidation states also reaches a maximum near the center of each series. They can vary by only one unit whereas nonmetals typically vary by two. ns (n-1)dFor metals on the left side, both the ns and (n-1)d electrons can be involved in reactions. Because elements near the middle of each transition series have many oxidation states, much of the chemistry of these elements involves redox reactions.
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  • 24 - 12 Oxidation states Hg +2 +1 Hg +2 +1 Cd +2 Cd +2 Zn +2 Zn +2 Au +3 +1 Au +3 +1 Ag +1 Ag +1 Cu +2 +1 Cu +2 +1 Hf +4 Hf +4 Zr +4 Zr +4 Ti +4 +3 +2 Ti +4 +3 +2 Lu +3 Lu +3 Y +3 Y +3 Sc +3 Sc +3 Pt +4 +2 Pt +4 +2 Pd +4 +2 Pd +4 +2 Ni +2 Ni +2 Ir +4 +3 Ir +4 +3 Rh +4 +3 +2 Rh +4 +3 +2 Co +3 +2 Co +3 +2 Os +8 +6 +4 Os +8 +6 +4 Ru +8 +6 +4 +3 Ru +8 +6 +4 +3 Fe +3 +2 Fe +3 +2 Re +7 +6 +4 Re +7 +6 +4 Tc +7 +6 +4 Tc +7 +6 +4 Mn +7 +6 +4 +3 +2 Mn +7 +6 +4 +3 +2 W +6 +4 W +6 +4 Mo +6 +4 +3 Mo +6 +4 +3 Cr +6 +3 +2 Cr +6 +3 +2 Ta +5 +4 Ta +5 +4 Nb +5 +4 +2 Nb +5 +4 +2 V +5 +4 +3 +2 V +5 +4 +3 +2
  • Slide 13
  • 24 - 13 Magnetic properties Many of the transition metals and their compounds have magnetic properties. ferromagnetic.Iron and to a lesser extent, cobalt and nickel are ferromagnetic. Can be permanently magnetized. paramagnetic.For most transition metals, at least one oxidation state is paramagnetic. Attracted to a magnetic field.
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  • 24 - 14 Magnetic properties Paramagnetic species have unpaired electrons. The magnitude of the effect depends on the number of unpaired electrons.Example Paramagnetic Cr [Ar] Diamagnetic Pd[Kr] 3 d 4s
  • Slide 15
  • 24 - 15 Formation of complexes and coordination compounds Formation of complexes is a characteristic property of transition metals. The most easily observed property of transition metal complexes is color. The color is dependent on the identity of the central atom, its oxidation state and the type of ligand. Coordination compounds. Those that include one or more complexes.
  • Slide 16
  • 24 - 16 Complexes Alfred Werner studied the formation of coordination compounds of platinum. He found that one mole of platinum(IV) chloride would combine with 2, 3, 4, 5 or 6 moles of ammonia. PtCl 4. 2NH 3 PtCl 4. 3NH 3 PtCl 4. 4NH 3 PtCl 4. 5NH 3 PtCl 4. 6NH 3 This format was used to show the proportions of PtCl 4 and NH 3 that had combined.
  • Slide 17
  • 24 - 17 Complexes Werner observed that the reactivities of the five coordination compounds differed. For example, addition of silver nitrate resulted in differing amounts of AgCl being formed. PtCl 4. 2NH 3 (aq) + excess Ag + no reaction PtCl 4. 3NH 3 (aq) + excess Ag + 1 AgCl PtCl 4. 6NH 3 (aq) + excess Ag + 4 AgCl This indicated that some of the chlorides must be bound to Pt.
  • Slide 18
  • 24 - 18 Complexes Werner defined the coordination number as the number of atoms or groups that are firmly bound to the central atom. Empirical Number Number Number of Formulaof ions of Cl - nonionic Cl PtCl 4. 6NH 3 5 4 0 PtCl 4. 5NH 3 4 3 1 PtCl 4. 4NH 3 3 2 2 PtCl 4. 3NH 3 2 1 3 PtCl 4. 2NH 3 0 0 4
  • Slide 19
  • 24 - 19 Complexes To indicate bound verses free ions, an alternate format for the formula was developed. [Pt(NH 3 ) 6 ]Cl 4 [PtCl(NH 3 ) 5 ]Cl 3 [PtCl 2 (NH 3 ) 4 ]Cl 2 [PtCl 3 (NH 3 ) 3 ]Cl [PtCl 4 (NH 3 ) 2 ] Coordinated atoms and groups are placed inside square braces. Free ions are placed on the outside. The symbol for the central atom is placed first. Ionic then neutral ligands are then listed in that order. Coordinated atoms and groups are placed inside square braces. Free ions are placed on the outside. The symbol for the central atom is placed first. Ionic then neutral ligands are then listed in that order.
  • Slide 20
  • 24 - 20 Stereoisomerism in complexes Werner also evaluated the arrangement of coordinated groups around the central atom. He found that for one of the platinum complex, [PtCl 2 (NH 3 ) 2 ], two different isomers were observed. This could only be explained if the geometry was square planer.
  • Slide 21
  • 24 - 21 Stereoisomerism in complexes Two geometric isomers were observed for [PtCl 2 (NH 3 ) 2 ]. cis-[PtCl 2 (NH 3 ) 2 ]trans-[PtCl 2 (NH 3 ) 2 ]
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  • 24 - 22 Stereoisomerism in complexes Some complexes exist in enantiomeric forms. To determine the number of forms that can exist, do the following. Draw or use a model kit to develop different geometric forms for your complex. Make a mirror image for each geometric isomer. If the model and its mirror image can be superimposed, they represent the same compound If they cant be superimposed, they represent different compounds.
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  • 24 - 23 Example 1 The left and right forms can be superimposed. They represent the same compound. Original modelMirror image
  • Slide 24
  • 24 - 24 Example Original modelMirror image The left and right forms cant be superimposed. They represent the different compound.
  • Slide 25
  • 24 - 25 Polydentate ligands and chelate complexes Ligands can be classified by dentate number - number of bonds/ligandMonodentate 1 bond/ligand - ammoniaBidentate 2 bonds/ligand - ethylene diamineMultidentate variable number based on need EDTA
  • Slide 26
  • 24 - 26 Monodentate ligands Possess only one accessible donor group. H 2 O is a good example since all metal ions exist as aqua complexes in water. Although two e - pairs are available, only one is accessible. The other will always point the wrong way
  • Slide 27
  • 24 - 27 Monodentate ligands Some aqua complexes Ag(H 2 O) 2 + Cu(H 2 O) 4 2+ Fe(H 2 O) 6 3+ The charge and coordination number are NOT related. Fe(H 2 O) 6 2+ also exists.
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  • 24 - 28 Monodentate ligands Common monodentate ligands anionic neutral X - OH - H 2 O SCN - RCOO - NH 3 CN - S 2- RNH 2
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  • 24 - 29 Bidentate ligands Form two bonds to central species. A good example is ethylene diamine. NH 2 CH 2 CH 2 NH 2 - (en) The amine groups are far enough apart to permit both to interact. Zn 2+ + 2 en Zn CN CN CN CN
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  • 24 - 30 Bidentate ligands Other common bidentate ligands. 8 - hydroxyquinoline O-O- N Zn 2+ + 2 O N Zn 2
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  • 24 - 31 Bidentate ligands Other common bidentate ligands. Dimethylglyoxime - dmg
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  • 24 - 32 Bidentate ligands Ni (dmg) 2
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  • 24 - 33 Bidentate ligands 1,10 phenanthroline
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  • 24 - 34 Bidentate ligands Iron(II) 1,10-phenanthroline complex
  • Slide 35
  • 24 - 35 EDTA Ethylenediamine tetraacetic acid A commonly used ligand. Forms