Structural Impact of Multitopic Third-Generation Bis(1-pyrazolyl)methane Ligands: Double, Mononuclear Metallacyclic Silver(I) Complexes

The reaction of 1,2,4,5-tetrakis(bromomethyl)benzene and hexakis(bromomethyl)benzene with the alkoxide of 2,2-bis(1-pyrazolyl)ethanol leads to the synthesis of the new polytopic ligands 1,2,4,5-C6H2[CH2OCH2CH(pz)2]4 (Ltetra, pz = pyrazolyl ring) and C6[CH2OCH2CH(pz)2]6 (Lhexa). Reactions of these ligands and the appropriate silver(I) salt lead to the preparation of [Ag2Ltetra](BF4)2 (1), [Ag2Ltetra](SO3CF3)2 (2), [Ag3Lhexa](BF4)3 (3), and [Ag3Lhexa](ClO4)3 (4). The solid-state structures of four different complexes crystallized from solutions of 1 or 2 yield five independent structures of the [Ag2Ltetra]2+ cation, all with similar structures. In all of the structures, two para-oriented pairs of “arms” (−CH2OCH2CH(pz)2) from a single ligand each chelate a silver(I) ion on the opposite sides of the arene ring, forming a double, mononuclear metallacyclic structure of two 17-membered rings connected by the central arene ring. The structures about the silver(I) cations in these complexes are distorted tetrahedral. The flexibility of the ligand leads to two types of arrangements of the linking arms in the five complexes. The central cations of the two Lhexa complexes also form double, mononuclear metallacycles, but the structures are different from those of the silver complexes of Ltetra in that both Lhexa cations contain one para-linked and one meta-linked metallacycle, thus forming a 16- and a 17-membered ring. In addition, the two remaining arms on Lhexa coordinate with additional silver(I) cations, linking the double, mononuclear metallacycles into a coordination polymer network.