The geometric structures of Pd-complexes {Pd([9]ane
B2A)
L2 and Pd([9]ane
BAB)
L2 where
A = P, S;
B = N;
L = PH
3, P(CH
3)
3, Cl
−}, their selective orbital interaction towards equatorial or axial (soft
A…Pd) coordination of macrocyclic [9]ane
B2A tridentate to Pd
L2, and electron density transfer from the electron-rich
trans L-ligand to the low-lying unfilled a
1g(5s)-orbital of Pd
L2 were investigated using B3P86/lanl2DZ for Pd and 6-311+G** for other atoms. The pentacoordinate
endo-[Pd([9]ane
B2A)(
L-donor)
2]
2+ complex with an axial (soft
A--Pd) quasi-bond was optimized for stability. The fifth (soft
A--Pd) quasi-bond between the σ-donor of soft
A and the partially unfilled a
1g(5s)-orbital of Pd
L2 was formed. The pentacoordinate
endo-Pd([9]ane
B2A)(
L-donor)
2]
2+ complex has been found to be more stable than the corresponding tetracoordinate
endo-Pd complexes. Except for the
endo-Pd pentacoordinates, the tetracoordinate Pd([9]ane
BAB)
L2 complex with one equatorial (soft
A-Pd) bond is found to be more stable than the Pd([9]ane
B2A)
L2 isomer without the equatorial (
A-Pd) bond. In particular, the geometric configuration of
endo-[Pd([9]ane
PNP)(
L-donor)
2]
2+ could not be optimized.
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