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tallic coordination polymer {[(NO3)Nd(H2O)4(m3-cydta)Bi-(m-
ONO2)]·2.5H2O}n, where cydta is trans-cyclohexylene-1,2-diami-
netetraacetate.[30]
of the BiIII ion, which evidently projects in a direction that
roughly bisects the O1-Bi1-O4 bond angle (inset to Figure 4). If
the 6s2 lone pair is treated as occupying one coordination site,
each symmetry-unique BiIII ion labelled Bi1 in 2 should be re-
garded as seven-coordinate with the remaining coordination
sites occupied by the four sulfur atoms of the bidentate 3,4-di-
hydroisoquinoline-2(1H)-carbodithioate ions and the two ni-
trate ion oxygen atoms O1 and O4.
The intrachelate S-Bi-S bond angles of 1 average 66.4(2)8,
consistent with the mean of 65(2)8 for related structures in the
literature.[27] The coordination group of each BiS4 unit is com-
pleted by one O atom of a nitrate ion (BiÀO1 2.723(4) ꢁ). How-
ever, the coordination geometry around BiIII in 1 is distinctly ir-
regular, and defies typical classification. Each nitrate ion func-
tions as a bridging ligand in the 1D chain by virtue of coordi-
nation of its second oxygen atom to the adjacent BiIII ion in
the lattice (Figure 3). The extended structure may thus be de-
scribed as a 1D coordination polymer comprising alternating
BiS4 repeat units and bridging nitrate ions. Interestingly, the in-
version-related 1D polymer chain interacts significantly with its
counterpart through weaker (longer) Bi···S interactions (3.31 ꢁ).
Note that the sum of the van der Waals radii[31] of Bi (2.54 ꢁ)
and S (1.89 ꢁ) far exceeds the Bi···S interaction distance in 1,
consistent with the interaction being effectively a dative cova-
lent bond. This results in the formation of columns comprising
symmetry-related pairs of 1D chains whose axes run parallel to
one another but in opposite directions. The obtuse O1i-Bi-O3ii
bond angle of 125.28 (Figure 3) suggests, furthermore, that the
BiIII valence lone pair (6s2) may be stereochemically active in 1,
as in soft scorpionate[32] and tetraphenylimidodiphosphinate[33]
chelates of BiIII, and is most likely positioned midway between
the two nitrate ion O donors (projecting approximately out of
the plane of Figure 3 towards the reader). This electron-density
projection is in fact clearly supported by the difference Fourier
map for 1 shown in the Supporting Information (Figure S3). It
is common to count the lone pair as occupying one coordina-
tion site at the metal centre for BiIII coordination com-
pounds.[34] Applying this principle here suggests that the BiIII
ions of 1 are in fact eight-coordinate. Interestingly, there are
some well-characterised BiIII coordination complexes in the lit-
erature with geometries that clearly indicate the presence of
the stereochemically active 6s2 lone pair of BiIII; however, its
contribution to the irregular coordination geometry around
the metal ion is apparently not always recognised.[35] A sound
theoretical basis (s–p mixing of metal-cation and oxide-ligand
atomic orbitals) exists to account for the variable appearance
of the lone pair in Sb2O3 and other 6s2 metal oxides (e.g.,
PbO),[36] but has seemingly not yet been extended to a molecu-
lar orbital treatment of lone-pair effects in large coordination
complexes of BiIII with complex ligands such as those described
in this work.
The coordination geometry around the second symmetry-
unique BiIII ion, Bi2, is markedly different to that of Bi1. For ex-
ample, the O1-Bi2-O4i bond angle is 85.8(1)8 and the structural
distortion around Bi2 appears to be less severe. Since we
cannot be certain of the existence of a stereochemically active
6s2 electron pair for Bi2 (as suggested by the more diffuse elec-
tron density distribution about Bi2, see Figure S4 of the Sup-
porting Information), the coordination number around Bi2 is
best regarded as being definitively six. The BiÀS bond lengths
for 2 range from 2.603(1) to 2.810(2) ꢁ (av 2.70(8) ꢁ), in agree-
ment with those of 1 and other similar BiIII chelate complexes
in the literature.[27] The BiÀO bond lengths average 2.74(4) ꢁ,
À
consistent with the bridging nature of the NO3 ions in the
structure, as noted for 1. The S-Bi-S bond angles for 2 average
66.3(5)8, are similar to those of 1 and in close agreement with
S-Bi-S intrachelate angles observed for related compounds in
the CSD.[27,37] For both 1 and 2, the CÀS bond lengths are stat-
istically equivalent, averaging 1.74(1) and 1.72(1) ꢁ, respective-
ly, consistent with the expected resonance-delocalised elec-
tronic structure of the dithiocarbamate ions in both com-
pounds.
The crystal packing in 2 is somewhat loose, presumably be-
cause of the inherent difficulty of efficiently packing the large
tetranuclear cluster. The total solvent-accessible volume per
unit cell is 227.5 ꢁ3 (4.8%), and the total electron count within
the void space is 19.9 electrons; this equates to two water
molecules per unit cell. Due to their disorder, the water mole-
cules occupying the two larger void spaces (2ꢂ51.4 ꢁ3;
Figure 5) were not discretely modelled during structure refine-
ment. The smaller void spaces (2ꢂ25.7 ꢁ3, 4ꢂ10.1 ꢁ3, and 4ꢂ
8.2 ꢁ3) are vacant.
The reaction between Bi(NO3)3·4H2O and piperidinedithiocar-
bamate in water followed by recrystallisation from chloroform/
methanol afforded complex 3. A thermal ellipsoid view of the
crystal structure of the bis-chloroform solvate of tris(piperidine-
dithiocarbamato)bismuth(III) (3; space group P21/c), is shown
in the Supporting Information (Figure S5). Crystal data, data
collection and structure refinement details for complex 3 (two
independent molecules per ASU) are summarised in the Sup-
porting Information (Table S1). The independent bismuth(III)
ions are bound to six sulfur donor atoms, each from three che-
lating dithiocarbamate ligands. The coordination geometry
about each BiIII ion reflects an uneven distribution of the three
chelate rings due to formation of a dimer comprising the two
crystallographically independent molecules in the lattice (Sup-
porting Information, Figure S6). The dimer is stabilised by intra-
molecular Sb···S interactions with distances of 3.367(1) ꢁ
(Bi2···S4) and 3.402(1) ꢁ (Bi1···S8); the B1-S4···Bi2-S8 and S4-
Bi1···S8-Bi2 dihedral angles of 45.53(3) and 45.46(3)8, respec-
Complex 2 is a centrosymmetric tetranuclear BiIII cluster with
bridging nitrate groups (m1,h1-NO3À, Figure 4). Because the ge-
ometry about the centre of gravity of the cluster is opened
out by the bridging nitrate ions, no acutely short Bi···S intra-
molecular interactions are evident. The shortest of these,
Bi1···S1i (3.650(1) ꢁ, symmetry code i: Àx, Ày, Àz), is probably
too long to be considered even a weak dative covalent bond,
despite the contact distance lying within the sum of the van
der Waals radii of the bonded elements. Consistent with 1, the
obtuse O1-Bi1-O4 bond angle of 133.7(1)8 probably signals the
presence of the stereochemically active nominally 6s2 lone pair
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Chem. Eur. J. 2016, 22, 1 – 10
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