Preparation, characterization, and X-ray crystal structures of helical and syndiotactic zinc-based coordination polymers

Engineering the structure and magnetic properties of crystalline solids via the metal-directed self-assembly of a versatile molecular building unit

We report the supramolecular chemistry of several metal complexes of N-(4-pyridyl)benzamide (NPBA) with the general formula [Ma(NPBA)2AbSc], where M = Co2+, Ni2+, Zn2+, Mn2+, Cu2+, Ag+; A = NO3-, OAc-; S = MeOH, H2O; a = 0, 1, 2; b = 0, 1, 2, 4; and c = 0, 2. NPBA contains structural features that can engage in three modes of intermolecular interactions: (1) metal-ligand coordination, (2) hydrogen bonding, and (3) pi-pi stacking. NPBA forms one-dimensional (1-D) chains governed by hydrogen bonding, but when reacted with metal ions, it generates a wide variety of supramolecular scaffolds that control the arrangement of periodic nanostructures and form 1- (2-4), 2- (5), or 3-D (6-10) solid-state networks of hydrogen bonding and pi-pi stacking interactions in the crystal. Isostructural 7-9 exhibit a 2-D hydrogen bonding network that promotes topotaxial growth of single crystals of their isostructural family and generates crystal composites with two (11) and three (12) different components. Furthermore, 7-9 can also form crystalline solid solutions (M,M')(NPBA)2(NO3)2(MeOH)2 (M, M' = Co2+, Ni2+, or Zn2+, 13-16), where mixtures of Co2+, Ni2+, and Zn2+ share the same crystal lattice in different proportions to allow the formation of materials with modulated magnetic moments. Finally, we report the effects that multidimensional noncovalent networks exert on the magnetic moments between 2 and 300 K of 1-D (4), 2-D (5), and 3-D (7, 8, 10, and 13-16) paramagnetic networks.

Supramolecular assemblies of dimetal complexes with polydentate N-donor ligands: from a discrete pyramid to a 3D channel network

Reactions of a dinuclear metal complex in the form of dirhodium(II) tetra(trifluoroacetate), [Rh(2)(O(2)CCF(3))(4)] (1), with a number of strong N-donor ligands having functional groups rigidly oriented at different directing angles have been found to yield supramolecular architectures of differing complexity. All structures have been established by X-ray crystallography. From reaction of 1 with neutral tris(4'-pyridyl)methylsilane ligand, CH(3)Si(C(5)H(4)N)(3) (L1), a discrete pyramid-shaped hexanuclear complex [[Rh(2)(O(2)CCF(3))(4)](3)CH(3)Si(C(5)H(4)N)(3)(eta(1)-C(6)H(6))(3)].C(6)H(6) (2.C(6)H(6)) has been isolated from benzene. In 2 three molecules of 1 are strongly coordinated to one L1 ligand at only one axial position of each dirhodium unit at the Rh-N distances of 2.152(6) A. The second rhodium atom of each dimetal complex in 2 weakly coordinates a benzene molecule with an Rh-C distance of 2.69(2) A. A supramolecular complex of the composition [[Rh(2)(O(2)CCF(3))(4)](2)(C(6)H(5))(2)Si(C(5)H(4)N)(2)] (3) has been prepared by reacting the dinuclear units 1 with a potentially bidentate ligand, bis(4'-pyridyl)diphenylsilane, (C(6)H(5))(2)Si(C(5)H(4)N)(2) (L2), having two pyridyl groups rigidly oriented at 109 degrees. In 3, one L2 ligand coordinates two dirhodium molecules 1 through their axial positions with the Rh-N distance of 2.150(5) A. An interesting extended 2D layered motif is formed by additional contacts of open axial positions of dirhodium units with phenyl groups of the neighboring ligands at Rh-C distances which average to 2.88(1) A. A supramolecular compound of the composition [[Rh(2)(O(2)CCF(3))(4)](3)(HO)C(C(5)H(4)N)(3)(eta(1)-C(6)H(6))].(1)/(2)C(6)H(6) (4.(1)/(2)C(6)H(6)) has been formed when linear dirhodium units 1 were reacted with tris(4'-pyridyl)methanol (L3) having tetrahedral directing angles that average to 110 degrees. A building block in the solid structure of 4 is a hexanuclear molecule in which one L3 ligand binds three dimetal units of 1 through N atoms of pyridyl groups at the average Rh-N distance of 2.143(7) A. A unique extended pseudo-3D structure in 4 is created by additional Rh-O coordination bonds as well as by weak metal-arene interactions.

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

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.

Alternating right- and left-handed helical loops in a self-assembled polymer: direct observation of ring-opening polymerization of a macrocyclic gold complex

Reaction of the ligand NN'-bis(pyridin-3-yl)-1,3-benzenedicarboxamide (1) with the diphosphanedigold(I) complex [(mu-PP)(AuO2CCF3)2] occurred by displacement of the trifluoroacetate ligands by the pyridyl groups of 1, and crystallization gave the macrocyclic complex [Au2(mu-PP)(mu-1)](CF3CO2)2 (2b), when PP = trans-[Ph2PCH=CHPPh2] but the polymer [(Au2(mu-PP)(mu-1)]x](CF3CO2)2x (3), when PP= Ph2PCH2CH2PPh2. The polymer 3 contains a series of helical turns connected by linear chain sections. and the helices have alternating right- and left-handed conformations. The polymer 3 dissolves to give an equilibrium mixture of the macrocyclic ring complex [Au2(mu-PP)(mu-1)](CF3CO2)2 (2a), and ring-opened oligomers, thus giving insight into the mechanism of the ring-opening polymerization reaction.

Crucial influence of solvent and chirality-the formation of helices and three-dimensional nets by hydrogen-bonded biimidazolate complexes

Deprotonation and recrystallisation of racemic [Co(2,2'-biimidazole)3][NO3]3 by ammonia in water/dimethylformamide solutions gave crystals of [Co(Hbiim)3] x 0.8H2O x 0.5DMF (2: Hbiim = monoanion of 2,2'-biimidazole, DMF = dimethylformamide), a porous material that contains fourfold interpenetrating (10.3) three-dimensional nets formed by neutral, hydrogen-bonded [Co(Hbiim)3] units, with DMF molecules in the narrow channels. Recrystallisation of [delta-Co(2,2'-biimidazolate)3] gave helices instead of the expected (10,3)-a net. These results are discussed in the light of additional density functional theory and molecular mechanics calculations and the X-ray structure of [Co(H2biim)3][NO3]3.

Tethered pyrazolyl phosphinate: pyrazolyl-N- and phosphoryl-O-metal coordination in Ph(2)P(O)[OCH(2)CH(2)(3,5-Me(2)Pz)]

Phosphorus pyrazolides, P(O)(3,5-Me(2)Pz)(3) or RP(E)(3,5-Me(2)Pz)(2) [E = S or O, R = Me or Ph], are hydrolytically sensitive particularly upon interaction with transition metal ions. In this paper, we report a new tethered pyrazolyl phosphinate, Ph(2)P(O)[OCH(2)CH(2)(3,5-Me(2)Pz)] DPEP (1), where the pyrazolyl group is separated from the phosphorus by means of an ethyleneoxy spacer. 1 has two potential coordination sites in the form of a phosphoryl oxygen atom and a pyrazolyl nitrogen atom. 1 forms hydrolytically stable complexes, (DPEP-CoCl(2))(n)(2), (DPEP)(2)-CuCl(2) (3), (DPEP-ZnCl(2))(n )(4), and (DPEP)(2)-PdCl(2) (5). The cobalt(II) and the zinc(II) complexes 2 and 4 show a zigzag polymeric structure in the solid state with a tetrahedral coordination geometry around the metal ion; the ligand DPEP coordinates through its phosphoryl oxygen and the pyrazolyl nitrogen to two neighboring metal ions and functions as a bridging ligand to form the polymeric structure. In contrast to 2 and 4, the copper(II) and the palladium(II) complexes 3 and 5 show a square-planar geometry around the metal ion. Exclusive coordination through the pyrazolyl nitrogens of the ligand 1 is observed. An extensive supramolecular sheetlike two-dimensional polymeric network is observed in the solid-state structures of 3 and 5 as a result of two weak interactions: (a) an intermolecular C-H- - -O interaction involving the phosphoryl oxygen and an aromatic C-H and (b) a pi-pi face-to-face stacking interaction between the phenyl groups of two adjacent molecules.

Supramolecular daisy chains

Two series of self-complementary daisy chain monomers, in which a secondary ammonium ion-containing arm is grafted onto a macrocycle with either a [24]- or [25]crown-8 constitution, have been synthesized. In the solid- and 'gas'-phases, the parent [24]crown-8-based monomer forms dimeric superstructures, as revealed by X-ray crystallography and mass spectrometry, respectively. Elucidation of the complicated solution-phase behavior of this compound was facilitated by the synthesis and study of both deuterated, and fluorinated, analogues. These investigations revealed that the cyclic dimeric superstructure also dominates in solution, except when extremes of either concentration (low), temperature (high), or solvent polarity (highly polar, e.g., dimethyl sulfoxide) are employed. Whereas, upon aggregation, the [24]crown-8-based daisy chain monomers have the capacity to form stereoisomeric superstructures further complicating the study of this series of compounds. The assembly of [25]crown-8-based monomers gives only achiral superstructures. The weaker association exhibited between secondary dialkylammonium ions and crown ethers with a [25]crown-8 constitution, however, resulted in limited oligomerization--only dimeric and trimeric superstructures were formed at experimentally attainable concentrations--of [25]crown-8-based daisy chain monomers.

Self-assembly with postmodification: kinetically stabilized metalla-supramolecular rectangles

Interaction of a predesigned molecular "clip" (4) with rigid dipyridyl bridging ligands, in acetone/water mixtures, leads to the formation of molecular rectangles (5-8) in 92-97% isolated yields via spontaneous self-assembly. Characterization was accomplished with multinuclear NMR and UV-vis spectroscopy, FAB mass spectrometry, and X-ray crystallography. The length of these metallamacrocycles ranges from 2 to 3 nm. Postmodification via non-nucleophilic counterion exchange results in enhanced structural integrity for the assemblies.