Chapter 19 Transition Metals and Coordination Chemistry
The Differences between Main Group Metals and Transition Metals • Transition metals are more electronegative than the main group metals. • The main group metals tend to form salts. The transition metals form similar compounds, but they are more likely than main group metals to form complexes. NaCl(s)→ Na+(aq)+Cl-(aq) CrCl3(s) + 6 NH3(l) →CrCl3 · 6 NH3(s) Violet Yellow
Sc: [Ar]4s23d1 Ti: [Ar]4s23d2 V: [Ar]4s23d3 Cr: [Ar]4s13d5 Mn: [Ar]4s23d5 Fe:[Ar]4s23d6 Co:[Ar]4s23d7 Ni: [Ar]4s23d8 Cu: [Ar]4s13d10 Zn:[Ar]4s23d10 Electron Configurations
Half Filled Set of 3d Orbitals • Cr: [Ar]4s13d5 Cu: [Ar]4s13d10 • The orbital energies are not constant for a given atom but depend on the way that the other orbitals in the atom are occupied. Because the 4s and 3d orbitals have similar energies, the 4s23dn and 4s13dn+1. configurations have similar energies. • For most elements, 4s23dn is lower in energy, but for Cr and for Cu the 4s13dn+1 is more stable.
Oxidation States • Co:[Ar]4s23d7 Co2+: [Ar]3d7 Co3+:[Ar]3d6 • The discussion of the relative energies of the atomic orbitals suggests that the 4s orbital has a lower energy than the 3d orbitals. Thus, we might expect cobalt to lose electrons from the higher energy 3d orbitals, but this is not what is observed. • In general, electrons are removed from the valence-shell s orbitals before they are removed from valence d orbitals when transition metals are ionized.
Lanthanide Contraction • Since the 4f orbitals are buried in the interior of these atoms, the additional electrons do not add to the atomic size. • The increasing nuclear charge causes the radii of lanthanide elements (Z=58-71) to decrease significantly going from left to right.
Ligands • A ligands is a neutral molecule or ion having a lone pair that can be used to form a bond to a metal ion. • Because a ligand donates an electron pair to an empty orbital on a metal ion, the formation of a metal-ligand bond (coordinate covalent bond) can be described as the interaction between a Lewis base (the ligand) and a Lewis acid (the metal ion).
Structural IsomerismCoordination Isomers • Isomers involving exchanges of ligands between complex cation and complex anion of the same compound. [Co(NH3)6][Cr(CN)6] & [Co(CN)6][Cr(NH3)6] [Ni(C2H4)3][Co(SCN)4] & [Ni(SCN)4][Co(C2H4)3] [Cr(NH3)5SO4]Br& [Cr(NH3)5Br]SO4
Structural IsomerismLinkage Isomers • Isomers in which a particular ligand bonds to a metal ion through different donor atoms. [Co(NH3)5ONO]Cl2&[Co(NH3)5NO2]Cl2
Stereo-isomerismGeometric Isomers/cis-trans Isomers • Stereoisomers: Molecules have the same molecular formula and the same connectivity of atoms, but differ only in the three-dimensional arrangement of those atoms in space. • Geometric Isomers:Atoms or groups of atoms can assume different positions around a rigid ring or bond.
Stereo-isomerismOptical Isomer • Optical isomerism is a form of isomerism whereby the different 2 isomers are the same in every way except being non-superimposable mirror images(*) of each other.
The two structures are nonsuperimposable mirror images. They are like a right hand and a left hand.
Simple substances which show optical isomerism exist as two isomers known as enantiomers. • A molecule which has no plane of symmetry is described as chiral. The carbon atom with the four different groups attached which causes this lack of symmetry is described as a chiral center. chiral center
One enantiomer will rotate the light a set number of degrees to the right. This is called the Dextrorotator (from the Latin dexter, "right"右旋) isomer or (+) isomer. The other enantiomer will rotate the plane polarized light the same number of set degrees in the opposite left direction. This isomer is said to be a Levorotatory (from the Latin laevus, "left“左旋) isomer or (-) isomer.
Octahedral Complexes eg t2g
Strong Field and Low Spin • The splitting of d orbital energies explains the color and magnetism of complex ions. • If the splitting produced by the ligands is very large, a situation called strong field case, the electrons will pair in the low energy t2g orbitals. • The strong field case is also called low spin case. • This gives a diamagnetic complex in which all electrons are pairs. • △0>P
Weak Field and High Spin • If the splitting produced by the ligands is small, the electrons will occupy all five orbitals before pairing occurs called weak field case. • The weak field case is also called high spin case. • In this case, the complex is paramagnetic. • △0<P
Octahedral transition-metal ions with d1, d2, or d3 configurations
Octahedral transition-metal ions with d4, d5, d6, and d7 configurations
For octahedral d8, d9, and d10 complexes , there is only one way to write satisfactory configurations.
weak fieldcasestrong fieldcase with paramagnetic with diamagnetic
The Color of Complexes • Very commonly for the first transition series, the energy corresponds to that of visible light, so that d-d transitions are the cause of the delicate colours of so many of the complexes.