Self-assembled Transition Metal Coordination Frameworks of ...

Chapter 3
angles N(1)—Ni(1)—S(1), N(5)—Ni(l)—S(2) and N(2)—Ni(l)—N(6) are 159.12(13),
l59.64(l4) and l68.86(19)° respectively, while in compound 6a these angles N(1)—
Ni(l)—S(l), N(5)—Ni(l)—S(2) and N(2)—Ni(l)—N(6) are 158.54(l4), l58.79(l4) and
l65.8(2)° respectively. These factors suggest considerable distortion from an
octahedral geometry around Ni(II) center in both the complexes.
The bond lengths Ni__Nazo, Ni—Np,, and Ni-S in 6a increase in that order as in
similar compounds [44-47]. A similar increase is seen in the quinoline substituted
compound 5- 2‘/zH;O. The Ni—Nqu bonds are of the same strength as both show
2.139(5) A and weaker compared to Ni_-Npy bonds in compound 6a. The Ni—N,,,° bond
lengths are smaller compared to that of Ni—Np,,q,, in complexes 5- 2‘/zH2O and 6a,
indicating the higher strength of former bond than the latter. The Ni-S bond lengths in
complex 5- 2‘/zH2O are found smaller compared to that in 6a indicate stronger bonds
in 5- 2‘/zH2(). However the C-S bond lengths in 6a are greater compared to the
1.681(3) A seen in the free ligand HL8 [48] and also compared to that in compound 5­
2‘/zH2O. Also the C—N bond lengths in 6a {1 .334(8) A for N(3)-—C(l3) and 1.371(8) A
for C(30)—N(7)} are consistent with partial double bond character. These factors
confirm the coordination through the thiolate form by deprotonation after enolization
of ligand HL8 in compound [Ni(L8)2] (6a). However in 5- 2%H2O, the coordination
occurs via thione form of HL7 as evidenced by the smaller C-S and higher C—N,“
bond lengths. These bond lengths are comparable to that seen in thiosemicarbazones
with delocalization of electron density [49].
In complex 5- 2'/2H2O the molecules are connected by various hydrogen
bonding interactions including water molecules (Table 3.11) and are packed in the
lattice (Fi g. 3.27) in an ordered ITl3I1I1€I‘ along the c axis by making use of C—H---1t ring
interactions. VVhile in compound 6a, the molecules are packed in the same manner
along the a axis as seen in Fig. 3.28, as a result of one intermolecular hydrogen
bonding interaction and diverse C—H---1t ring interactions (Table 3.12). However, no
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