Question

Four-coordinate metals can have either a tetrahedral or a square-planar geometry; both possibilities are shown here for \(\left[\mathrm{PtCl}_{2}\left(\mathrm{NH}_{3}\right)_{2}\right] .\) (a) \(\mathrm{What}\) is the name of this molecule? (b) Would the tetrahedral molecule have a geometric isomer? (c) Would the tetrahedral molecule be diamagnetic or paramagnetic? (d) Would the square-planar molecule have a geometric isomer? (e) Would the square-planar molecule be diamagnetic or paramagnetic? (f) Would determining the number of geometric isomers help you distinguish between the tetrahedral and square-planar geometries? (g) Would measuring the molecule's response to a magnetic field help you distinguish between the two geometries? [Sections 23.4-23.6 ]

Short answer

The given complex is called diamminedichloroplatinum(II). A tetrahedral molecule does not have geometric isomers and is diamagnetic. A square-planar molecule can have geometric isomers (cis and trans) and is also diamagnetic. Determining the number of geometric isomers would help in distinguishing between the tetrahedral and square-planar geometries, but measuring the molecule's response to a magnetic field would not.

Step-by-step solution

(a) Naming the complex

The given complex is \(\left[\mathrm{PtCl}_{2}\left(\mathrm{NH}_{3}\right)_{2}\right]\). The name of this complex is "diamminedichloroplatinum(II)" following the IUPAC nomenclature rules, where the ligands are named alphabetically, and the overall charge is indicated in roman numerals.

(b) Geometric isomers in a tetrahedral molecule

In a tetrahedral molecule, there are no possible geometric isomers as ligands will always be in the same arrangement, equidistant from each other.

(c) Magnetic properties of the tetrahedral molecule

The tetrahedral molecule would be diamagnetic because all the valence electrons in the metal ion and ligands are paired and there are no unpaired electrons in the complex.

(d) Geometric isomers in a square-planar molecule

The square-planar molecule can have geometric isomers. In a square-planar geometry, two types of isomer can exist: cis and trans isomers. The difference between the two configurations occurs when the ligands are in either adjacent positions (cis) or opposite positions (trans) to each other.

(e) Magnetic properties of the square-planar molecule

The square-planar molecule would also be diamagnetic because all the valence electrons in the metal ion and ligands are paired and there are no unpaired electrons in the complex.

(f) Distinguishing geometries through geometric isomers

Determining the number of geometric isomers would help in distinguishing between the tetrahedral and square-planar geometries, as the tetrahedral molecule does not have any geometric isomers while the square-planar molecule can have geometric isomers (cis and trans).

(g) Distinguishing geometries through magnetic properties

Measuring the molecule's response to a magnetic field would not help in distinguishing between the two geometries, because both the tetrahedral and square-planar molecules are diamagnetic, exhibiting no response to a magnetic field as they have no unpaired electrons.

Key concepts

Geometric Isomers

Understanding geometric isomers is key in coordination chemistry, as they are one of the ways to differ between different molecular structures. Geometric isomerism occurs due to the arrangement of ligands around a central atom in a complex ion.

For instance, in a square-planar complex like \(\left[\mathrm{PtCl}_{2}\left(\mathrm{NH}_{3}\right)_{2}\right]\), it is possible to have the chloro and ammine ligands adjacent to one another (cis) or opposite each other (trans), resulting in different chemical and physical properties. However, in a tetrahedral complex, such isomerism is not observed, since all four positions around the central atom are equivalent, leading to a single possible arrangement of the ligands regardless of how they are rotated or flipped.

Identification of geometric isomers is vital because it can significantly influence the reactivity and function of a chemical species. This concept is particularly useful for students who aim to understand molecular geometries in inorganic chemistry and the role of stereochemistry in the properties and function of compounds.

Magnetic Properties of Complexes

Magnetic properties provide insight into the electronic structure of coordination complexes. They indicate whether unpaired electrons are present (paramagnetism) or absent (diamagnetism).

In the case of the \(\left[\mathrm{PtCl}_{2}\left(\mathrm{NH}_{3}\right)_{2}\right]\) complex, both the tetrahedral and square-planar geometries exhibit diamagnetism, which means all electrons are paired within the complex and it will not be attracted to a magnetic field.

An understanding of magnetic behavior in coordination compounds is essential, not only in predicting how a complex will respond to a magnetic field but also in inferring the electronic configuration of the central metal ion. As a learning tip, when studying coordination complexes, students should be mindful of the electron count, as it directly correlates with the magnetic properties of the complex.

IUPAC Nomenclature of Coordination Compounds

Up-to-date knowledge of IUPAC nomenclature rules for coordination compounds is imperative for clear and accurate communication in the field of chemistry.

The naming convention follows a specific order: the ligands are named first in alphabetical order, then the central metal atom, with its oxidation state indicated in roman numerals in parentheses. Ionic charges, if present, are not referenced in the name but rather in the overall formula. For the given complex \(\left[\mathrm{PtCl}_{2}\left(\mathrm{NH}_{3}\right)_{2}\right]\), the name diamminedichloroplatinum(II) follows this convention, specifying 'ammine' for the \(\mathrm{NH}_{3}\) ligands and 'chloro' for the \(\mathrm{Cl}\) ligands, while 'platinum(II)' indicates the central metal and its oxidation state.

Understanding and applying the IUPAC naming rules are important for students not only in solving textbook exercises but also in future scientific writing and discourse. It ensures uniformity and reduces confusion in the vast and complex landscape of chemical compounds.