what is the complex that forms between Co2+ and SCN-1 with a coordination number of 4

what is the complex that forms between Co2+ and SCN-1 with a coordination number of 4

The correct answer and explanation is:

The complex that forms between Co²⁺ (cobalt(II) ion) and SCN⁻ (thiocyanate ion) with a coordination number of 4 is commonly represented as [Co(SCN)₄]²⁻. This is a coordination complex where the Co²⁺ ion acts as the central metal ion, and the SCN⁻ ions function as ligands, bonding to the metal ion via their sulfur (S) or nitrogen (N) atoms.

To explain the formation of the complex:

1. Coordination Chemistry: The cobalt(II) ion, Co²⁺, has a d⁷ electron configuration, making it capable of forming complexes by donating its empty orbitals to coordinate with electron-pair donors such as ligands. In this case, SCN⁻ acts as a bidentate ligand, meaning it can coordinate through both sulfur and nitrogen, although, in some cases, it may bind only through one atom (usually sulfur).
2. Structure of the Complex: The coordination number of 4 suggests that the cobalt ion forms a square planar or tetrahedral geometry. In this case, it’s typically square planar, with the four SCN⁻ ions surrounding the central cobalt ion. These ligands arrange themselves symmetrically around the Co²⁺ ion, bonding primarily through the sulfur atom in the thiocyanate ion.
3. Bonding and Charge Distribution: The thiocyanate ion, SCN⁻, is a monodentate ligand in many cases, meaning it donates a single electron pair to the metal center. However, the sulfur atom in SCN⁻ is more electronegative than nitrogen, so it often acts as the primary site of coordination in these complexes.
4. Properties of the Complex: The resulting [Co(SCN)₄]²⁻ complex has interesting properties, including specific absorption spectra, which can be studied using UV-Vis spectroscopy. These complexes are often intensely colored due to d-d transitions within the metal ion.
5. Stability: The stability of this complex is influenced by the size and charge of the Co²⁺ ion, the nature of the SCN⁻ ligand, and the coordination environment. The formation of a four-coordinate complex with SCN⁻ is common in many transition metal chemistry reactions.

In summary, the complex that forms between Co²⁺ and SCN⁻ with a coordination number of 4 is [Co(SCN)₄]²⁻, with a square planar geometry, where the Co²⁺ ion is coordinated by four thiocyanate ions, likely through sulfur atoms. This complex is often studied in coordination chemistry due to its distinct properties.