Synthesis of and Structural Studies on Lead(II) Cysteamin Complexes

The novel compounds PbCl2·(SCH2CH2NH3) (1), Pb(SCH2CH2NH2)2·2PbCl(SCH2CH2NH2) (2), and Pb(SCH2CH2NH2)2 (3) were synthesized by reaction of PbO or PbCl2 with [HSCH2CH2NH3]Cl and NaOH, and were characterized
by elemental analysis, IR-, and UV/vis-spectroscopy. Single-crystal X-ray diffraction revealed different coordination
modes for the two Pb atoms in 2. The Pb atom in the Pb(SCH2CH2NH2)2 unit forms two covalent Pb−S and two
intramolecular dative Pb···N bonds, leading to a pseudo trigonal bipyramidal configuration with a stereochemically
active lone pair. The Pb atom in the PbCl(SCH2CH2NH2) unit, the first moiety structurally characterized of the
PbCl(SR) type (R = organic group), forms covalent Pb−Cl and Pb−S bonds, an intramolecular dative Pb···N
bond, and two intermolecular Pb···S contacts, giving a pseudo octahedral configuration with a stereochemically
active lone pair as well. Despite the Pb(SCH2CH2NH2)2 moiety exhibiting C2 symmetry in 2, and C1 symmetry in
3, its structural parameters are rather similar in the two compounds. The influence of the Pb···N bond on molecular
structure and thermodynamic stability were estimated by means of quantum chemical ab initio methods. Although
an analysis of the wave function in terms of natural bond orbitals (NBO) revealed that n(N) and np(S) compete for
the empty p-orbital of the PbII atom, the σ-type n(N)−6p(Pb) interaction is stronger than the π-type np(S)−6p(Pb)
interaction and hence determines the conformation of the compounds.