Using multimodal ligands to influence network topology in silver(I) coordination polymers

Abstract

A range of Ag(I) one-and two-dimensional coordination frameworks has been prepared and structurally characterized by using the multimodal ligand 3,6-di-pyrazin-2-yl-(1,2,4,5)-tetrazine, which offers both monodentate and chelating binding sites. It is demonstrated that multimodal ligands can be used to prepare coordination frameworks with novel and unusual topologies and to influence the precise geometrical arrangement of both ligands and metal centers within such supramolecular arrays.crystal engineering ͉ supramolecular chemistry ͉ tetrazine T he synthesis of coordination frameworks represents an extremely topical area of research (1-3) that has developed dramatically over recent years with many advances in understanding the control of framework structure and topology. For example, the degree of interpenetration (4), polymeric dimensionality (5), and framework connectivity (6) can be controlled by the design of the constituent building blocks or crystallization conditions. We (7,8), among others (9-13), have been developing a strategy that uses multimodal bridging ligands that differ from more traditional tri-and tetradentate bridging systems in that they offer chemically distinct binding sites, both chelating and monodentate (Scheme 1). By using such ligands for coordination polymer construction, we aim to introduce further control over network formation by controlling the precise arrangement of metal centers with respect to each other and have recently reported examples of chiral Ag(I) coordination frameworks with diamondoid topology by using 2,2Ј-bipyrazine as the multimodal bridging ligand (7,8). We are also interested in the assembly of discrete supramolecular entities, metallacycles, or oligomeric supramolecular arrays into infinite coordination arrays (13). Our recent studies combining coordinatively flexible Cd(II) metal centers with the angular ligand 2,4Ј-(1,4-phenylene)bispyridine indicate that centrosymmetric metallacyclic units can be readily prepared by using simple ligand design (13). The latter study (13) also demonstrated that the metallacyclic units could be arranged into coordination frameworks by means of bridging of coordinated NO 3 Ϫ anions (13). We are now extending this work to use ligands that simultaneously encourage the formation of metallacyclic units and also intermetallacycle bridging.We have targeted 3,6-di-pyrazin-2-yl-(1,2,4,5)-tetrazine (dpztz), which has the potential to control the relative displacement of up to four coordinated metal centers in a zigzag fashion (Scheme 2). Although bis-2-pyridyl substituted 1,2,4,5-tetrazine units in principle allow coordination of two metal centers in cis-bidentate sites, in practice this coordination mode has never been observed and the trans-arrangement is always adopted (14-16). Dpztz also has the potential to form metallacyclic units with a suitably flexible transition metal, such as Ag(I), using both chelating and monodentate donors (Scheme 2e). It is our experience that Ag(I) exhibits a marked tendency to adopt both chelating and mono...

Structural Diversity in One-dimensional Coordination Polymers of a Flexible Multimodal Ligand

“…The N donor atom in the 4-position acted as a monodentate ligand as in 1, 2 and 4. This tendency for metal ions to adopt both chelating and monodentate donors with multimodal ligands has been attributed to the drive towards a "homogeneous" metal coordination environment throughout the coordination polymer [14]. Two of our examples, 1 and 3, were in accord with this notion of a "homogeneous" metal coordination environment.…”

“…The Ag···S distances to the other Ag(I) ions of 3.4700(10) and 3.6256(10) Å were well outside possible bonding values. Although Ag(1) and Ag (4) were surrounded by both chelating and monodentate donors from the multimodal ligands the remaining two Ag(2) and Ag (3) ions were not and so the environment of the Ag(I) ions was not "homogeneous" throughout the polymer [14]. Although the chains were crystallographically distinct, there were only small differences in bond lengths and angles throughout the chains and the chains were essentially the same as each other.…”

“…The ligand used all available lone pairs on each donor atom, including both on the S donor, and coordinated to four Ag(I) cations. Thus, the Ag(I) ion was surrounded by both chelating and monodentate donors from the multimodal ligands giving rise to a "homogeneous" metal coordination environment throughout the one-dimensional polymer [14]. The ligand L adopted an endo-anti conformation with the pyridine rings almost parallel to each other with a tilt of 2.88 and the planes of the pyrazine rings 2.81 Å apart with a centroid-to-centroid distance of 5.622(1) Å .…”

A Structural Investigation of Anion–Triazole Interactions: Observation of “π‐Pockets” and “π‐Sandwiches”

“…For example, a number of metal complexes of 3,6-di(2-pyridyl)-1,2,4,5-tetrazine (dptz) or 3,6-di(2-pyrazinyl)-1,2,4,5-tetrazine (dpztz) have been prepared by the groups of Dunbar [9,32,33] and Champness [34] that contain an anion-tetrazine-anion arrangement with centroid-anion distances as short as 2.75 Å for both anions. It is worth noting, however, that in most structures there is an "excess" of anion, when compared with π-deficient aromatic rings, particularly given that one anion may be involved in interactions with a number of π-rings.…”

Triflate anion and ligand influences in silver(i) coordination polymers of four isomeric dipyridyl ketone oximes

“…[1][2][3][4] For example, the area of 1D coordination polymers has been thoroughly reviewed recently. [6][7][8][9][10] Thus the main focus has largely been on the binding arrangements of the bridging ligand entities and their interactions with the metal ions. [6][7][8][9][10] Thus the main focus has largely been on the binding arrangements of the bridging ligand entities and their interactions with the metal ions.…”