The
half-lantern PdII
2 complexes trans-(O,C)-[Pd(ppz)(μ-O∩N)]2 (1) and trans-(E,N)-[Pd(ppz)(μ-E∩N)]2 (E∩N is a deprotonated 2-substituted
pyridine; E = S (2), Se (3); Hppz = 1-phenylpyrazole)
were cocrystallized with 1,4-diiodotetrafluorobenzene (FIB) to give
cocrystals 1·(FIB) and (2−3)·2(FIB); the parent complexes and the cocrystals were
studied by X-ray crystallography. The crystal structure of trans-(O,C)-1·FIB is assembled mainly by the I···O halogen
bonding (XB) to give the [@PdII
2]O···I(areneF)I···O[@PdII
2] linkage,
while trans-(E,N)-(2–3)·2(FIB) are built by
the joint action of I···Pd and I···E
XBs, thus furnishing the PdII
2···I(areneF)I···E[@PdII
2] (E = S,
Se) cluster. Detailed theoretical (DFT) studies with the application
of the QTAIM, ELF, NBO, IGM, SAPT, and HSAB methods revealed several
types of attractive noncovalent interactions in the cocrystals, namely,
the I···Pd, I···E (E = O, S, Se), I···C,
π–π-stacking, and π···F interactions.
I···Pd is a rare type of XB involving the metal center
as an XB acceptor, the Pd···Pd communication facilitating
the I···Pd bonding. The I···Pd and I···E
bonds are comparable in strength (the bond interaction energies being
between −7 and −13 kcal/mol), but the former is controlled
by dispersion forces, while the latter is mostly governed by an electrostatic
term.