Silver(I) Complexes in Coordination Supramolecular System with Bulky Acridine-Based Ligands: Syntheses, Crystal Structures, and Theoretical Investigations on C−H···Ag Close Interaction

In our efforts to investigate the coordination architectures of transition metals and organic ligands with tailored
structures, we have prepared two structurally related rigid bulky acridine-based ligands, 9-[3-(2-pyridyl)pyrazol-1-yl]- acridine (L1) and 9-(1-imidazolyl)acridine (L2), and synthesized and characterized four of their Ag(I) complexes,
{[AgL1](ClO4)}2 (1), {[AgL1](NO3)}2 (2), [AgL22](ClO4) (3), and {[(Ag3L23)(NO3)](NO3)2(H2O)}∞ (4). The single-crystal X-ray diffraction analysis shows that the structures of 1 and 2 are similar to each other, with the two
intramolecular Ag(I) centers of each complex being encircled by two L1 ligands; this forms a unique boxlike cyclic
dimer, which is further linked to form one-dimensional (1D) chains of 1 and a two-dimensional (2D) network of 2
by intermolecular face-to-face π···π stacking and/or weak C−H···O hydrogen-bonding interactions, respectively.
3 has a mononuclear structure, which is further assembled into a 2D network via intermolecular Ag···O and π···π
stacking weak interactions. 4 possesses two different 1D motifs that are further interlinked through interlayer face-to-face π···π stacking and Ag···O weak interactions, resulting in a 2D network. It is worth noting that one of the
interesting structural features of 1, 2, and 4 is the presence of obvious C−H···M hydrogen-bonding interactions
between the Ag centers and some acridine ring H atoms identified by X-ray diffraction on the basis of the van der
Waals radii. Furthermore, as a representative example, full geometry optimization on the basis of the experimental
structure, the natural bond orbital (NBO), and topological analysis of 1 were carried out by DFT and AIM (Atoms
in Molecules) calculations. The total C−H···Ag interaction energy in 1 is estimated to be about 14 kJ/mol. Therefore,
this work offers three new rare examples (1, 2, and 4) that exhibit C−H···Ag weak interactions, in which the N
donors of the acridine rings coordinate to Ag(I) ions. Also, these results strongly support the existence of
C−H···Ag close interactions and allow us to have a better understanding of the nature of such interactions in the
coordination supramolecular systems.