Full- or Half-Encapsulation of Sulfate Anion by a Tris(3-pyridylurea) Receptor: Effect of the Secondary Coordination Sphere

Abstract

Self-assembly of the [Fe(DABP)(3)]SO(4) (DABP = 5,5'-diamino-2,2'-bipyridine) or [Fe(bipy)(3)]SO(4) (bipy = 2,2'-bipyridine) complex with a tripodal tris(3-pyridylurea) ligand (L) results in a layered structure that includes a sulfate anion in the cleft of one L molecule. The two compounds, [Fe(DABP)(3)][SO(4) L] x 10 H(2)O (2) and [Fe(bipy)(3)][SO(4) L] x 9 H(2)O (3), show very similar sheets formed by the anionic units [SO(4) L](2-) and cationic building blocks ([Fe(DABP)(3)](2+) or [Fe(bipy)(3)](2+)). However, there are different water clusters that link the adjacent layers in the two products, that is, water parallelograms and quasi "water cubes" in 2 versus single water molecules, water dimers, and hexamers in 3. The half-encapsulation of sulfate by a single L molecule contrasts with the previously reported full-encapsulation of the sulfate ion by two L molecules in [M(H(2)O)(6)][SO(4) L(2)] (1). This different anion encapsulation is traced to the hydrogen-acceptor properties of the pyridyl groups of L together with the hydrogen-bonding properties of the cation secondary coordination sphere for a solid-state packing optimization. In 1 the direct hydrogen bonding from the secondary coordination sphere of octahedral [M(H(2)O)(6)](2+) to L-pyridyl helps in the formation of an octahedral cation-anion coordination in the NaCl-type structure. In 2 and 3, crystal water instead of the cations has to satisfy the hydrogen-accepting demands of L. Consequently, a non-spherical and only partly water-surrounded half-encapsulated [SO(4) L](2-) anion allows for a closer approach of the [Fe(DABP)(3)](2+) or [Fe(bipy)(3)](2+) cations than the [SO(4) L(2)](2-) anion. Then, the similar cation and anion size in 2 and 3 with the Coulomb attraction confined to a two-dimensional plane leads to the formation of a hexagonal BN (or graphite) lattice. Competition experiments with different anions for compound 2 reveal that SO(4)(2-) can be selectively crystallized against NO(3)(-), OAc(-), or ClO(4)(-).

Unexpected Self‐Sorting Self‐Assembly Formation of a [4:4] Sulfate:Ligand Cage from a Preorganized Tripodal Urea Ligand

“…In this capsule,h ydrogen bonding is the dominant interaction that holds the self-assembled structure together.T hese interactions consist of both urea NÀH···O(S) hydrogen bonds,w ith average bond lengths of 2.22 ( Table S2) and hydrogenbonding interactions between SO 4 2À and the protonated anilines,A r-NH 3 + ···O(S). [13] As was the case in the SO 4 2À complexes of 1-3,t he carboxamide oxygen atoms of 4 are oriented away from the cavity in the same manner to that seen for 2 (Figure 1), demonstrating that the 1,3,5-benzenetricarboxamide central platform remains the foundation for the preorganization of both molecules.S ome of the carboxamide oxygen atoms also interact with at otal of three water molecules in the asymmetric unit, as well as as ingle CH 3 CN molecule. Among the total of eight urea moieties,s ix of them are doubly hydrogen bonded to as ingle SO 4 2À ion and two of them are singly bonded to two different SO 4 2À ions (Scheme S2).…”

Metal ion binding patterns of acyclovir: Molecular recognition between this antiviral agent and copper(II) chelates with iminodiacetate or glycylglycinate

“…Hence the crystal of 1 is a H-bonded 3D-framework. It should be noted that the referred hydrogen bonds are charged-assisted, which are generally one of the strongest, wherein the H-bond donor and/or acceptor carry positive and negative ionic charges respectively [39][40][41][42][43].…”

Influence of noncovalent interactions on the structures of metal–organic hybrids based on a [VO2(2,6-pydc)]− tecton with cations of imidazole, pyridine and its derivatives

“…The covalent approach is primarily based on strong coordinate bonds connecting metal cations and organic ligands into robust polymeric structures. 16 However, protonated organic cations can also act as multi-hydrogen bond donors as well as acceptors and thus easily adjust the topologies via additional non-covalent interactions. 1 In the non-covalent approach much weaker forces, such as hydrogen bonding, C-HÁ Á Áp/F interactions, pÁ Á Áp stacking, and halogen bonding, are employed.…”