Unusual Carbonyl···Carbonyl Interaction in Supramolecular Structures of Silver(I) Complexes with 2,6-Pyridinediylbis(4-pyridinyl)methanone

A series of silver(I) complexes of a higher homologue of di-2-pyridyl ketone, 2,6-pyridinediylbis(4-pyridinyl)methanone (abbreviated as L), consisting of {[Ag(L)(BF4)]·H2O}∞ (1), {[Ag(L)(NO3)]·H2O}∞ (2), [Ag3(L)2(NO2)3(H2O)]∞ (3), [Ag(L)]2(PF6)2 (4), {[Ag(L)(CO2CF3)]2}∞ (5), [Ag(L)]2(SO3CF3)2 (6), and [Ag(L)]2(CO2CF2CF3)2 (7), have been synthesized and characterized. Complexes 1 and 2 are isomorphous helical polymers, 3 is a metallacycle featuring a trisilver(I) core, and 4−7 are isostructural complexes containing a common dinuclear [Ag2(L)2]2+ metallacyclic skeleton. All complexes except 4 feature a common dominant intermolecular multipolar carbonyl···carbonyl interaction, which along with argentophilic Ag(I)···Ag(I), π···π, hydrogen-bonding, Ag···OC, O(trifluoroacetate)···CO as well as unconventional CO···π and anion-π(pyridyl) interactions assemble the different coordination motifs (1−3, 5−7) into higher-dimensional frameworks. Three principal types of carbonyl···carbonyl interaction exhibiting antiparallel, sheared parallel, and perpendicular motifs are observed, and unusual supramolecular associations such as “···[CO···CO]n···” (in 1−2 and 6) and “···[CO···CO···π]n···” (in 3) and “CO···CO···CO” (in 7) are the novel structural features established in these complexes. The geometrical parameters and role of such noncovalent interactions in the construction of the present series of supramolecular metal−organic frameworks are discussed.