Question

The following borate \([B_5O_6(OH)_4]^-\) belongs to which of the following class of borates?

Hint:

Most common polyborates found in minerals like borax are mixed borates containing both tetrahedral and trigonal planar boron centers.

Answer 1

Step 1: Understanding the Concept:
Polyborates are classified based on the coordination number of the Boron atoms within their complex structure.
Step 2: Detailed Explanation:
The pentaborate anion \([B_5O_6(OH)_4]^-\) consists of a bicyclic structure. In this arrangement, one boron atom is 4-coordinated (\(sp^3\), tetrahedral \(BO_4\) unit) while the other four boron atoms are 3-coordinated (\(sp^2\), trigonal planar \(BO_3\) units). Because the structure contains boron atoms in different hybridization and coordination states, it is termed a "Mixed" borate.
Step 3: Final Answer:
The class of borate is Mixed.