Functionalization of Semiconductor Surfaces

CHAPTER 8

Dative Bonding of Organic Molecules

YOUNG HWAN MIN, HANGIL LEE, DO HWAN KIM, AND SEHUN KIM

8.1 INTRODUCTION

8.1.1 What is Dative Bonding?

A dative bond is a coordinate covalent bond between atoms such that both bonding electrons are contributed by only one of the atoms involved in the bond. In other words, dative bonding occurs when one atom donates an electron pair and the other atom accepts the electron pair, and the atoms share the electrons equally. This bonding mode is distinct from ionic bonding modes. The donating atom is called a Lewis base (an electron pair donor) and the accepting atom is called a Lewis acid (an electron pair acceptor). Formation of a dative bond is, therefore, a Lewis acid/Lewis base reaction or a nucleophilic/electrophilic reaction. One of the most well-known examples of dative bonding is the bond between ammonia (NH₃) and boron trifluoride (BF₃). The boron of BF₃ has only six valence electrons and requires two more electrons to satisfy the octet rule. Due to this deficiency, BF₃ can act as a Lewis acid that accepts lone pair electrons. NH₃, on the other hand, can act as a Lewis base by donating its two lone pair electrons. Thus, NH₃ donates its two lone pair electrons to BF₃ to create a dative bond, NH₃:BF₃.

Interestingly, dative bonding occurs between Lewis bases (or Lewis acids) and reconstructed semiconductor surfaces such as Si(100)-(2×1), Ge(100)-(2×1), and Si(111)-(7×7). Semiconductor surfaces are prepared by cleavage and are reconstructed ...