The compound 1,1,1 -trifluoroacetylacetone (tfa) is a bidentate ligand: It forms a tetrahedral complex with \(\mathrm{Be}^{2+}\) and a square planar complex with \(\mathrm{Cu}^{2+}\). Draw structures of these complex ions and identify the type of isomers exhibited by these ions.

Coordination chemistry is a branch of inorganic chemistry that deals with the study of compounds formed between metal atoms and ligands—molecules or ions that can donate a pair of electrons to the metal atom. These compounds, known as coordination complexes, have a central metal atom or ion, termed the coordination center, surrounded by a set of molecules or ions called ligands.

Each ligand has at least one donor atom with a lone pair of electrons used to form a coordinate bond (also called a dative covalent bond) with the metal ion. Ligands can be monodentate, binding through a single donor atom, or polydentate, binding through multiple donor atoms. Bidentate ligands, like 1,1,1-trifluoroacetylacetone (tfa), bind through two donor atoms, which gives rise to specific geometry within the complex depending on the metal center and the coordination number (the total number of ligand donor atoms bonded to the central atom).

In the process of forming these complexes, the metal ion can exhibit different coordination geometries that are influenced by factors such as the size, charge, and electron configuration of the metal ion, as well as the nature and steric demands of the ligands.

A tetrahedral complex is a type of molecular geometry where the central metal atom is surrounded by four ligand donor atoms at the corners of a tetrahedron. The bond angles between the ligands are approximately 109.5-degree, characteristic of a sp3 hybridized central atom. This shape is commonly seen in complexes with a coordination number of four.

The exercise mentioned the formation of a tetrahedral complex with beryllium (\( \text{Be}^{2+} \) ion and the bidentate ligand tfa. Since tfa can bind to the metal center at two points, two ligands coordinate with the beryllium to satisfy the coordination number of four, giving rise to a tetrahedral geometry. This geometry is favoured due to the small size of the beryllium ion and its preference for a lower coordination number, which results in less steric crowding and lower ligand-ligand repulsion in the complex.

In contrast to the tetrahedral complex, a square planar complex features a central metal atom surrounded by ligands that form the corners of a square. This type of geometry is common with a coordination number of four, especially for d8 metal ions, such as nickel(II), palladium(II), platinum(II), and gold(III), and is also exemplified by the copper(II) complex in our exercise.

A square planar complex has bond angles of 90 degrees and is often associated with transition metals that have a larger size and can accommodate four ligands in one plane without substantial steric hindrance. The square planar shape is often stabilized by the electronic effects of the metal and ligands involved. In the case of the copper(II) complex with tfa, the two ligands once again bind through two coordination sites each. However, due to the differing electron configuration and spatial considerations of the copper ion compared to beryllium, the resulting complex is square planar rather than tetrahedral.