13-8
“Increased-Valence” Structures for Longer N-Centre Bonding Units
185
the estimate of an S-N single-bond length
35 is 1.67 Å. A 12-electron 8-centre
“increased-valence” bonding unit is present in “increased- valence” structure (71);
it involves the eight nitrogen
electrons
and the four S-S σ-electrons of (70).
“Increased-valence” descriptions of the bonding for other cyclic S-N compounds are described in Refs. 21 and 38.
13-8 (c) (SN) x : Polymerized Pauling “3-electron bonds” and Polymerized
6-Electron 4-Centre bonding units
The polymer (SN) x consists of layers of 2-dimensional chains of alternating
sulphur and nitrogen atoms. Each sulphur and nitrogen atom contributes respectively two π-electrons and one π-electron to form a 2x-centre π-electron bonding
unit within a 2-dimensional chain. For such a chain, the standard Lewis structures
are of type (72), from which we may generate the “increased- valence” structure
(74)
21 via structure (73) and the delocalizations indicated in structure (72).
Alternatively, we may also obtain (74) by writing down the “long- bond” structure
(75) with zero formal charges on all atoms, and then proceed to structure (74) via
structure (76) by delocalizing non-bonding sulphur electrons into adjacent S-N
bonding π-orbitals. Examination of structure (76) shows that “increased-valence”
structure (74) is constructed from polymerized Pauling “3-electron bond” structures for the S-N π-electrons. Alternatively, structure (74) may also be considered
to involve the polymerization of the 6-electron 4-centre “increased-valence” structures for the π-electrons of structure (73). “Increased-valence” structure (74)
involves partial double-bond character for each of the S-N bonds, which is in
accord with the measured bond-lengths
46 of 1.59 Å and 1.63 Å.
“Increased-Valence” Structures for Longer N-Centre Bonding Units
185
the estimate of an S-N single-bond length
35 is 1.67 Å. A 12-electron 8-centre
“increased-valence” bonding unit is present in “increased- valence” structure (71);
it involves the eight nitrogen
electrons
and the four S-S σ-electrons of (70).
“Increased-valence” descriptions of the bonding for other cyclic S-N compounds are described in Refs. 21 and 38.
13-8 (c) (SN) x : Polymerized Pauling “3-electron bonds” and Polymerized
6-Electron 4-Centre bonding units
The polymer (SN) x consists of layers of 2-dimensional chains of alternating
sulphur and nitrogen atoms. Each sulphur and nitrogen atom contributes respectively two π-electrons and one π-electron to form a 2x-centre π-electron bonding
unit within a 2-dimensional chain. For such a chain, the standard Lewis structures
are of type (72), from which we may generate the “increased- valence” structure
(74)
21 via structure (73) and the delocalizations indicated in structure (72).
Alternatively, we may also obtain (74) by writing down the “long- bond” structure
(75) with zero formal charges on all atoms, and then proceed to structure (74) via
structure (76) by delocalizing non-bonding sulphur electrons into adjacent S-N
bonding π-orbitals. Examination of structure (76) shows that “increased-valence”
structure (74) is constructed from polymerized Pauling “3-electron bond” structures for the S-N π-electrons. Alternatively, structure (74) may also be considered
to involve the polymerization of the 6-electron 4-centre “increased-valence” structures for the π-electrons of structure (73). “Increased-valence” structure (74)
involves partial double-bond character for each of the S-N bonds, which is in
accord with the measured bond-lengths
46 of 1.59 Å and 1.63 Å.