Passage
Amino acids and copper both serve vital roles in many biological processes of living organisms. Beyond their separate biological roles, however, chemists have also discovered that amino acids are able to function as chelates with Cu²⁺ ions to form blue complexes with potential medicinal applications. One such complex, copper(II) glycinate, has shown to be effective against some oral diseases. The reaction to form copper(II) glycinate is shown in Figure 1.
Figure 1 Synthesis of two isomers of copper(II) glycinateTwo different isomers can form depending on the reaction conditions. Mixing hot aqueous glycine (70 °C) with a hot solution of copper(II) acetate dissolved in 50% aqueous ethanol, followed by cooling the mixture on ice, yields a precipitate of only the cis isomer. If a suspension of the cis isomer is held at boiling for an hour or longer in a solution of glycine and copper(II) acetate, the trans isomer is obtained.Because of the geometric differences between the two isomers, the stretching vibrations of the central Cu-N and Cu-O bonds in each isomer are different. Symmetric and asymmetric bond stretching give four possible vibrational modes for each isomer, as shown in Figure 2.
Figure 2 Vibrational modes of the coordinate bonds in copper(II) glycinateIf the stretching of the bonds during vibration causes a transient, unequal distribution of electron density between the atoms within the bond, an oscillating dipole will form. Bonds with dipoles that are not cancelled out by another dipole in the molecule will absorb infrared light at particular frequencies (often expressed in wave numbers) and are designated as IR-active. As a result, the vibrational differences between the two isomers can be analyzed by far-infrared (far-IR) spectroscopy, as shown in Figure 3.
Figure 3 Far-IR spectra of the cis and trans isomers of copper(II) glycinateBoth isomers show a skeletal absorbance (unrelated to coordinate bond vibration) near 385 cm⁻¹. Additional absorbance bands are seen that specifically relate to the vibrational modes of the bonds in each isomer.
-In metal complexes such as copper(II) glycinate, the coordination number refers to:

Question

Passage
Amino acids and copper both serve vital roles in many biological processes of living organisms. Beyond their separate biological roles, however, chemists have also discovered that amino acids are able to function as chelates with Cu²⁺ ions to form blue complexes with potential medicinal applications. One such complex, copper(II) glycinate, has shown to be effective against some oral diseases. The reaction to form copper(II) glycinate is shown in Figure 1.

Figure 1 Synthesis of two isomers of copper(II) glycinateTwo different isomers can form depending on the reaction conditions. Mixing hot aqueous glycine (70 °C) with a hot solution of copper(II) acetate dissolved in 50% aqueous ethanol, followed by cooling the mixture on ice, yields a precipitate of only the cis isomer. If a suspension of the cis isomer is held at boiling for an hour or longer in a solution of glycine and copper(II) acetate, the trans isomer is obtained.Because of the geometric differences between the two isomers, the stretching vibrations of the central Cu-N and Cu-O bonds in each isomer are different. Symmetric and asymmetric bond stretching give four possible vibrational modes for each isomer, as shown in Figure 2.

Figure 2 Vibrational modes of the coordinate bonds in copper(II) glycinateIf the stretching of the bonds during vibration causes a transient, unequal distribution of electron density between the atoms within the bond, an oscillating dipole will form. Bonds with dipoles that are not cancelled out by another dipole in the molecule will absorb infrared light at particular frequencies (often expressed in wave numbers) and are designated as IR-active. As a result, the vibrational differences between the two isomers can be analyzed by far-infrared (far-IR) spectroscopy, as shown in Figure 3.

Figure 3 Far-IR spectra of the cis and trans isomers of copper(II) glycinateBoth isomers show a skeletal absorbance (unrelated to coordinate bond vibration) near 385 cm⁻¹. Additional absorbance bands are seen that specifically relate to the vibrational modes of the bonds in each isomer.
-In metal complexes such as copper(II) glycinate, the coordination number refers to:

Quizplus · Accepted Answer

11ecba2d_120d_0393_a3bf_371024bc5d1e_MD0008_00 Coordinate covalent bonds, unlike covalent bonds, are formed between two atoms when both of the shared electrons are donated by the same atom. Such coordinate bonds are often formed between electron-poor metal ions and molecules called ligands that contain one or more electron-rich atoms with available lone-pair electrons. The coordinately bonded metal and its ligands are called a complex. As originally defined by Alfred Werner, the coordination number of a metal complex refers to the number of coordinate bonds formed between the central metal ion and its nearest neighboring atoms. When all of these nearest neighboring atoms are from separate molecules or ions, the number of ligands will equal the coordination number. However, if two or more of these nearest neighboring atoms are joined to the same coordinating ligand unit, then the number ligands will not equal the coordination number. In both cases, the number of nearest neighboring atoms and coordinate bonds is unchanged, but the number of ligand units is different. For example, if bonding interactions from other ligands such as water are excluded (as shown in Figure 1), both isomers of the copper(II) glycinate complex have a coordination number of 4. The Cu²⁺ atom has two oxygen atoms and two nitrogen atoms as its nearest neighbors, forming four coordinate bonds. However, each pair of N and O atoms is joined to the same glycine unit, and the four neighboring atoms come from only two glycine ligands. (Choice A) Copper(II) glycinate has only two ligands of glycine, but its coordination number is 4. (Choice C) The total number of electrons involved in the bonding does not directly describe the resulting coordination to the metal center. (Choice D) During the formation of a metal complex, the oxidation state (oxidation number) of the copper metal ion (+2) is unchanged. As such, the oxidation state does not describe the coordination number of the ligands to the metal center. Educational objective: Coordinate covalent bonds are formed between two atoms when one atom donates both shared electrons. Such bonds are often formed between electron-poor metal ions and electron-rich atoms in ligands in a complex, and the coordination number of the complex refers to the number of coordinate bonds formed with the metal ion.

Passage Amino Acids and Copper Both Serve Vital Roles in Many