Tuning Reactivity of Platinum(II) Complexes

5.2.8 Properties of the Ligands
Before discussing the results, it is worth looking at the properties of the ligand so as to
understand the forces at hand. The introduction of heteroatoms into a benzene ring
results in an irregular distribution of the electron density which strongly influences the
physical properties and reactivity of the ligand as well as the corresponding metal
complex. 38 In the case of diazines in these systems, two contradictory factors are in
place: the strong electron-acceptor influence of the nitrogen and the weak electron-
donor influence due to re-organisation of the π-cloud by inductive effect. The sequence
of the π-acceptor effect of these diazines decreases from pyrazine > pyridazine >
pyrimidine. 38 This is supported by the DFT –calculations on NBO charges and Pt-OH2
bond lengths (Table 5.1).
5.3 Results
5.3.1 Computation Calculations
Representative geometry-optimized structures for the complexes are shown in Figure 1.
Selected bond lengths and angles, natural atomic bond orbital (NBO) charges as well as
HOMO-LUMO energy gap are given in Table 5.1. From Table 5.1, it is observed that the
coordination around each of the Pt(II) atoms corresponds to a square-planar geometry
with slight distortions from ideal values according to the observed N–Pt–N and N–Pt–
OH2 angles. The optimized geometries are in agreement with the available
crystallographic structures of [{cis-PtCl(NH3)2}2-μ-pzn](ClO4)2/(NO3)2. 39,40 The Pt–N1/2
bond distance in all the complexes is found to be shorter than the Pt–Npy (2.159 Å)
distance in the mononuclear analogue Pt(pipNCN)2(py) + 41 (py = pyridine), which is an
indication that the diazine ligands have better π-acceptor properties compared to
pyridine. (Figure 5.1), π-back-bonding is of less or no significance in the complexes pzn,
pmn and pdn.
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