Crucial Role of the Counteranion on the Templation of Metallomacrocycles and a 3D Network:  Synthesis, Characterization, and Structural Analysis

Abstract

Two novel supramolecular architectures, [[Ag(2)L(1)(2)][X](2)] with X = CF(3)SO(3)(-) (2a) or X = NO(3)(-) (2b) and [[AgL(1)(2)][X]](n) with X = BF(4)(-) (3), were constructed by self-assembly and obtained in quantitative yields, using AgX as a building block and L(1) as the bridging ligand (L(1) = 1,3-bis(benzimidazol-1-ylmethyl)benzene). The X-ray molecular structures of 2a and 3 are reported. Complex 2a was identified as a metallomacrocycle in which one ligating triflate anion is coordinated to each of the two unsaturated Ag(I) ions. 2a crystallizes in monoclinic unit cell P2(1)/n with a = 9.728(6) A, b = 17.303(4) A, c = 13.268(3) A, beta = 92.52(4) degrees, V = 2231(2) A(3), and Z = 2. Remarkably, the X-ray structure of 2a shows a layered network structure consisting of infinite metallomacrocycles held together through pi-pi interactions between benzimidazole rings. In dramatic contrast, the product 3 prepared from AgBF(4) and L(1) lacks metal-counterion bonding, leading to a supramolecular 3D network with the following three outstanding features: (i) in one dimension, metallomacrocycles containing two Ag centers and two bridging ligands form infinite, double-stranded chains; (ii) neighboring chains are arranged by two distinct pi-pi interactions, one between substituted benzene rings and the other between benzimidazole rings, leading to a 3D structure; (iii) cavities within the 3D network contain BF(4)(-) counteranions. 3 crystallizes in monoclinic unit cell C2/c with a = 25.33(3) A, b = 11.655(6) A, c = 18.466(8) A, beta = 123.00(8) degrees, V = 4572(8) A(3), and Z = 4. Interestingly, electrospray mass spectroscopy suggests in either case that the identified elemental subunit [AgL(1)(2)](+) is the key building block which self-assembles and subsequent anion templation provides either the macrocycles 2a, b or the inorganic polymer 3. Remarkably, in dichloromethane solvent ligand-to-metal stoichiometries of 2:1 in 3 and 1:1 in 2a, b are obtained even with excess ligand, showing the power of metal-anion interactions in determining the overall supramolecular structure. Anion metathesis, showing supramolecular structural rearrangements from 2a to 2b and more spectacularly from 3 to 2b, smoothly occurred. The crucial effect and the nature of coordinating counteranions (BF(4)(-), CF(3)SO(3)(-), NO(3)(-)) on the supermolecule design are presented and discussed.