Mikki Vinodu

Self-assembly patterns of porphyrins in crystals. Structures of hydrogen-bonding and coordination polymers of manganese tetra(carboxyphenyl)porphyrin

Crystallizations of manganese-tetra(4-carboxyphenyl)porphyrin chloride from different reaction environments led to the formation of new extended polymeric architectures sustained either by cooperative hydrogen-bonding or by self-coordination of the porphyrin units. In one mode the manganese ion in the metalloporphyrin core coordinates axially from both sides to water molecules. The porphyrin species then associate to each other into open layered arrays by multiple hydrogen bonding between the carboxylic functions of adjacent units. The offset-stacked layers are tightly inter-linked (at an average spacing of 3.94 A) by additional hydrogen bonding between the apical water ligands of one array and the carboxylic groups of neighboring assemblies. Thus resulting interporphyrin organization represents a single-framework hydrogen-bonding polymer. The interporphyrin voids within the layers are accommodated by guest solvent components. In another mode, an unprecedented two-dimensional coordination polymer is assembled from the tetra-acid building blocks by direct coordination of the metalloporphyrin cores and carboxylic groups to the corresponding topical sites of adjacent species. Stacking of the polymeric layered arrays in the condensed crystalline phase incorporates molecules of crystallization solvent within the inter-layer voids.

Complexes of hexamethylenetetramine with zinc-tetraarylporphyrins, and their assembly modes in crystals as clathrates and hydrogen-bonding network polymers

This study reveals self-assembly patterns of the tetra(4-pyridyl), tetra(4-hydroxyphenyl) and tetra(4-carboxyphenyl) zinc porphyrin moieties when reacted with a hexamethylenetetramine ligand, forming 1 ∶ 1 five-coordinate, 1 ∶ 2 and 1 ∶ 2 six-coordinate complexes, respectively. Detailed structural characterization of the supramolecular organization in the resulting ordered solids is reported. Crystals of the 1 ∶ 1 complex (1) represent a common tetraarylporphyrin clathrate found earlier in the “porphyrin sponges”. Those of the 1 ∶ 2 complexes consist of multiporphyrin polymeric networks that are sustained by extensive hydrogen bonding, involving the four hydroxylic (in 2) or carboxylic (in 3) functional substituents as proton donors and the N-sites of the hexamethylenetetramine ligand as proton acceptors. The polymeric frameworks are characterized by three-dimensional (in 2) or two-dimensional (in 3) open architectures with wide interporphyrin voids; yet, they do not interpenetrate into one another, giving rise to the formation of open channels that perforate the corresponding crystals and are loosely occupied by guest species of the crystallization solvent. The pronounced effect of the hexamethylenetetramine ligand on the supramolecular aggregation is highlighted, by relating the current findings to previously designed networks of the porphyrin building blocks in question.

Supramolecular self-assembly of porphyrinic materials by design. Non-centrosymmetric architectures of the 5-(3′-pyridyl)-10,15,20-tris(4′-carboxyphenyl) and 5-(2′-quinolyl)-10,15,20-tris(4′-hydroxyphenyl) porphyrins

This study reports the design of polarized porphyrin network motifs sustained by mixed hydrogen bonding algorithms, aiming at the synthesis of non-centrosymmetric supramolecular architectures. It is based on suitably functionalized porphyrin scaffolds with mixed proton–donor and proton–acceptor groups that exhibit reduced C2/C2v point symmetry, in relation to the square-planar tetra-substituted 4′-carboxyphenyl, 4′-hydroxyphenyl or 4′-pyridyl porphyrin derivatives (D4h) widely utilized in the construction of porphyrin framework solids thus far. Representative examples are provided by supramolecular self-assembly of the free-base 5-(3′-pyridyl)-10,15,20-tris(4′-carboxyphenyl)-porphyrin (1) and 5-(2′-quinolyl)-10,15,20-tris(4′-hydroxyphenyl) porphyrin (2) moieties. In both cases, each porphyrin building block is connected to neighboring species in a cooperative but asymmetric manner by a combination of O–H⋯O and O–H⋯N inter-porphyrin hydrogen bonds, where optimization of the O–H⋯N interactions involves molecules related by twofold screw symmetry. This induces the formation of two-dimensionally networked arrays characterized by polarized intermolecular organization and by corrugated surfaces. Stacking of these layers along the normal direction is characterized by either translation or twofold screw symmetry, affording non-centrosymmetric crystal lattices with solvent species incorporated within the interporphyrin voids.

New assembly modes of porphyrin-based networks

The meso-5-pyridyl-10,15,20-tri(hydroxyphenyl)porphyrin has been synthesized and reacted with 1,2-dichloroethane to yield the corresponding pyridinium chloride salt with Npy-alkylated porphyrin building block. The latter undergoes self-assembly to form flat-networked patterns sustained by chloride anion auxiliaries, which attract cooperative hydrogen bonding from the hydroxylic functions of adjacent species. The O–H⋯Cl− attractions direct the structure of the multiporphyrin arrays, thus representing a useful synthon for the construction of extended porphyrin-based architectures. Tight stacking of the hydrogen-bonded polymeric layers in the axial direction is further stabilized by ion-pairing interactions.

Synthesis and versatile supramolecular self-assembly of the 5,15-bis(4-hydroxyphenyl)-10,20-bis(4-carboxyphenyl)porphyrin scaffold

This study reports the synthesis of the 5,15-bis(4-hydroxyphenyl)-10,20-bis(4-carboxyphenyl)porphyrin (BBP) moiety, and its versatile self-assembly into multiporphyrin hydrogen-bonding ‘polymers’ in four different reaction and crystallization conditions. In two cases the polymers are sustained by characteristic intermolecular cyclic dimeric (COOH)2 hydrogen-bond synthons between the carboxyphenyl functions of neighboring species, which face one another along a common equatorial axis of the porphyrin building blocks. The hydroxyphenyl substituents, which are directed perpendicular to the porphyrin chains, form either O–H⋯O(dioxane) or O–H⋯N(pyridine) weak hydrogen bonds by donating their protons to the solvent guest species. In the third example, the multiporphyrin chains are tessellated by rather unusual pairs of OH⋯OC(OH) hydroxyl–carboxyl hydrogen bonds between cis-related arms of adjacent porphyrin species along opposite directions of the polymer. Here the carboxylic protons are donated to the carbonyl site of the ethyl benzoate guest, thus linking the latter to the side surfaces of the polymeric chain. The fourth structure, which involves chain polymers of deprotonated porphyrin building blocks, is sustained by strong symmetric [–COO⋯H⋯OOC–]− hydrogen bonds along the chains. These chains aggregate further into complex three-dimensional architecture by weaker hydrogen bonds through bridging water molecules. The observed diversity of the intermolecular binding patters suggests that the BBP scaffold is not well suited for a programmed construction of network solids.

Porphyrin networks. Synthesis and supramolecular self-assembly of 5,10,15-tri(4-hydroxyphenyl)-20-(2-quinolyl) metalloporphyrins

The syntheses of a new asymmetrically functionalized porphyrin framework, the meso- 5,10,15-tri(4-hydroxyphenyl)-20-(2-quinolyl)porphyrin, and of its copper and aqua-zinc complexes are reported, along with a detailed structural characterization of the self-assembled architectures exhibited by the metalloporphyrin materials. Crystals of the two compounds consist of polymeric two-dimensional networks with similar connectivity features that are sustained by extensive hydrogen bonding, involving the three hydroxylic O-atoms as well as the quinolyl N-site. The layered assemblies have corrugated surfaces and pack in the form of intercalate structures, entrapping molecules of the nitrobenzene solvent within the interlayer voids. The results represent a relatively rare example of a successful formulation of extended multiporphyrin arrays based on asymmetric building blocks bearing different molecular recognition functions.

catena-Poly­[[bis­(pyridine-κN)­cobalt(II)]-μ-oxalato] 0.25-hydrate]

The structure of the title compound, {[Co(C2O4)(C5H5N)2]·0.25H2O}n, has been determined at ca 110 K with relatively high precision, revealing the polymeric aggregation mode of this species.

A low-temperature polymorph of [5,10,15,20-meso-tetrakis(4-chloro­phenyl)­porphyrinato-κ4N]­zinc(II) nitro­benzene clathrate

The title compound, [Zn(C44H24Cl4N4)]·C6H5NO2, crystallizes in several polymorphic forms. We report in this paper the third known polymorph of this compound, which can be obtained at temperatures below ca 195 K.