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A facile synthetic strategy for the generation of a new class of inorganic-organic-inorganic hybrids is reported. Replacement of labile DMSO ligands from the preformed Double-Four-Ring (D4R) zinc phosphate cluster [Zn(dipp){(CH3)2SO}]4 by the addition of 4-aminopyridine (4-ampyr) results in the isolation of another discrete D4R cluster [Zn(dipp)(4-ampyr)]4 (1), which forms a hydrogen-bonded framework in solid-state. If 1-methyl-4,4'-bipyridinium salts are employed instead, tetra-cationic D4R cluster [Zn(dipp)(L)]4[PF6]4 (2) and [Zn(dipp)(L)]4[ClO4]4 (3) (L = 1-methyl-4,4'-bipyridinium, dipp = 2,6-di-iso-propylphenylphosphate) are isolated. Compound 2 was reacted with three different polyoxometalates, [TBA]4[Mo8O26] (POM-1), [TBA]4[PMo11VO40] (POM-2), and [TBA]4[SiMo12O40] (POM-3) to obtain amorphous hybrids, [Zn(dipp)(L)]4[Mo8O26] (4), [Zn(dipp)(L)]4[PMo11VO40] (5), and [Zn(dipp)(L)]4[SiMo12O40] (6), respectively. All the hybrid materials have been characterized by analytical and spectroscopic studies. The molecular structure of 1 has also been determined by single-crystal XRD measurements. N2 gas sorption analyses show moderate BET surface area and also establish the mesoporous nature of the hybrids 4-6. The catalytic potential of hybrids 4, 5 and 6 has been explored towards epoxidation of cyclohexene.

Abstract: Double‐4‐ring zinc phosphate (D4R), [Zn(dipp)(4‐Py‐CHO)]4 (2) (dipp=diiminopyridine), bearing four formyl groups, has been utilized as a building block (SBU) for the synthesis of a new class of imine‐linked [4+2] COF‐like polycrystalline zinc phosphate frameworks. Reactions of 2 with a series of linear aromatic diamines results in the formation of polycrystalline frameworks [Zn4(dipp)4(L)2]n (3–6) (L=L1 to L4, diimines formed by condensation of 4‐pyridine carboxaldehyde with diamines). Employing an alternative synthetic strategy, through a diffusion‐controlled slow reaction of 2 with the pre‐synthesized 4,4‘‐bispyridyl bisimine (L3), [Zn4(dipp)4(L3)2]n (5′) has been obtained as single crystals. Complex 5′ is a 3D‐framework, exhibiting a rare eightfold interpenetrated diamondoid network. The long spacer length (19.6 Å) results in extensive entanglement in 5′. Powder diffraction data suggest that these compounds are isoreticular 3D‐frameworks. To study the effect of the relative position of pyridyl donors with respect to the central benzidine moiety, 3,3‘‐bispyridyl bisimine (L5) was investigated as the spacer. A slow reaction of 1 b with L5 leads to the isolation of a 2D‐boxed‐sheet coordination polymer [Zn4(dipp)4(L5)2]n (7). Selective formation of 3D‐framework 5′ from L3 and the 2D‐framework 7 from L5 is due to the angles created by the coordination of para‐ and meta‐pyridyl nitrogen centers at the zinc centers of the D4R cubane. Compound 5′ has been utilized as a catalyst for Knoevenagel condensation. [ABSTRACT FROM AUTHOR]

Reaction of Zn(OAc)2 ⋅2 H2O with 2,6-diisopropylphenyl phosphate (dippH2) in the presence of pyridine-4-carboxaldehyde (Py-4-CHO) in methanol resulted in the isolation of a tetrameric zinc phosphate cluster [Zn(dipp)(Py-4-CH(OH)(OMe))]4 ⋅4 MeOH ( 1) with four hemiacetal moieties stabilized on the double-4-ring inorganic cubane cluster. The change of solvent from methanol to acetonitrile leads to the formation of [Zn(dipp)(Py-4-CHO)]4 ( 2), in which the coordinated Py-4-CHO retains its aldehydic form. Dissolution of 1 in CD3CN readily converts it to the aldehydic form and yields 2. Similarly 2, which exists in the aldehyde form in CD3CN, readily converts to the hemiacetal form in CD3OD/CH3OH. Compound 1 is an unprecedented example in which four hemiacetals have been stabilized on a single molecule in the solid state retaining its stability in solution as revealed by its 1H NMR spectrum in CD3OD. The solution stability of 1 and 2 has further been confirmed by ESI-MS studies. To generalize the stabilization of multiple hemiacetals on a single double-four-ring platform, pyridine-2-carboxaldehyde (Py-2-CHO) was used as the auxiliary ligand in the reaction between zinc acetate and dippH2, leading to isolation of [Zn(dipp)(Py-2-CH(OH)(OMe))]4 ( 3). Understandably, recrystallization of 3 from acetonitrile yields the parent aldehydic form, [Zn(dipp)(Py-2-CHO)]4 ( 4). Single-crystal X-ray diffraction studies reveal that supramolecular bonding, aided by hydrogen-bonding interactions involving the hemiacetal functionalities (C−OH, C−OMe, and C−H), are responsible for the observed stabilization. The hemiacetal/aldehyde groups in 1 and 2 readily react with p-toluidine, 2,6-dimethylaniline, and 4-bromoaniline to yield the corresponding tetra-Schiff base ligands, [Zn(dipp)(L)]4 (L=4-methyl- N-(pyridin-4-ylmethylidene)aniline ( 5), 2,6-dimethyl- N-(pyridin-4-ylmethylene)-aniline ( 6), and 4-bromo- N-(pyridin-4-ylmethylene)aniline ( 7)). Isolation of 5- 7 opens up further possibilities of using 1 and 2 as new supramolecular synthons and ligands. [ABSTRACT FROM AUTHOR]

The reaction of Zn(OAc)2 ·2H2O with tert-butyl phosphonic acid ( tBuPO3H2) yields the zinc phosphonate [Zn( tBuPO3)(H2O)] ·H2O ( 1). X-ray diffraction studies reveals that compound 1 has a novel layered structural arrangement with the central zinc atoms in a tetrahedral coordination environment. This observation emphasizes the crucial role played by organic substituents on the coordination chemistry of phosphonic acid with transition metal ions. [ABSTRACT FROM AUTHOR]