Transition Metals and Coordination Compounds Flashcards

This set of vocabulary flashcards covers key concepts from the lecture on transition metals, coordination chemistry, isomerism, and crystal field theory.

Coordination compounds

An important class of transition metal compounds where a central metal ion is bound to one or more ligands and combined with counterions.

Ligand

A Lewis base (electron pair donor) that forms a coordinate covalent bond with a central metal ion.

Crystal field theory (CFT)

A bonding model for transition metal complexes that explains their colors and magnetic properties by focusing on the repulsions between ligand electrons and the d orbitals of the metal ion.

Coordination number

The number of molecules or ions directly bound to the central metal atom, also known as secondary valence.

Lanthanide contraction

The effect where third transition row elements are similar in size to second row elements because $(n-2)f$ electrons are ineffective at shielding the nucleus, causing outer electrons to be held more tightly.

Bidentate ligand

A ligand that can donate two pairs of electrons from two different atoms to a metal, such as the oxalate ion (ox) or ethylenediamine (en).

Polydentate ligand

A ligand that can donate more than two electron pairs to a metal ion, such as the hexadentate ligand ethylenediaminetetraacetate ($EDTA^{4-}$).

Chelate

A complex ion that contains either a bidentate or polydentate ligand.

Coordinate covalent bond

A bond formed when a ligand donates a pair of electrons to an empty orbital on a metal ion.

Structural isomers

Isomers in which atoms are connected in different ways, divided into coordination isomers and linkage isomers.

Coordination isomers

Structural isomers that occur when a coordinated ligand and an uncoordinated counterion exchange places.

Linkage isomers

Structural isomers with ligands that can coordinate to the metal through different atoms, such as the nitro ($NO_2^-$) and nitrito ($ONO^-$) forms.

Stereoisomers

Isomers where atoms have the same connectivity but different spatial arrangements, including geometric and optical isomers.

Geometric isomers

Stereoisomers where ligands have different spatial arrangements about the metal ion, such as cis-trans or fac-mer (facial-meridional) configurations.

Optical isomers

Nonsuperimposable mirror images, also called enantiomers, which exhibit optical activity by rotating polarized light.

Crystal field splitting energy ($\Delta$)

The difference in energy between split d orbitals in a complex ion, often calculated as $\Delta = \frac{hc}{\lambda}$.

Spectrochemical series

A list of ligands arranged in order of their ability to split d orbitals, ranging from strong-field ligands like $CN^-$ to weak-field ligands like $I^-$.

Strong-field complex

A complex where the crystal field splitting energy ($\Delta$) is large, leading to a low-spin configuration with fewer unpaired electrons.

Weak-field complex

A complex where the crystal field splitting energy ($\Delta$) is small, leading to a high-spin configuration with more unpaired electrons.

Heme

An iron complex containing a porphyrin ligand found in biological molecules like hemoglobin and cytochrome c.

Porphyrin

A flat, polydentate ligand with a planar ring structure containing four nitrogen atoms that coordinate to a central metal atom.

Cisplatin

The geometric isomer cis-$[Pt(NH_3)_2Cl_2]$ which acts as an effective anticancer agent by binding to DNA.