The electronic structure and bonding of the
N2S2 molecule are studied by the spin-coupled
valence bond
method. Unusual features are revealed which clarify much of the
hitherto puzzling properties of this molecule,
leading ultimately to a simple Lewis structure: The two N atoms of
the N2S2 ring bear a substantial negative
charge,
and the two S atoms, a complementary positive charge. There are
four single N−S σ bonds and two lone pairs of
π electrons, one pair centered about each N atom. Two further
π electrons, one from each of the S atoms, are
directly coupled to each other across the ring, giving the molecule the
overall character of a singlet diradical. This
last is shown to be closely related to the metallic character of the
(SN)
x
polymer.
ABSTRACT:The first core-optimized spin-coupled description of excited states is presented, based on the core-optimized spin-coupled theory of Gerratt and co-workers and the state-selective spin-coupled theory of Doggett et al. The approach realizes for excited states, for which Gerratt propounded for the ground state, a fully variational description with a single configuration of nonorthogonal orbitals and core orbitals. The model is applied to the 1 S e states of Be and to three low-lying states of Be
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