A [4+2] Condensation Strategy to Imine‐Linked Single‐Crystalline Zeolite‐Like Zinc Phosphate Frameworks

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 [Zn 4 (dipp) 4 ( L ) 2 ] n ( 3 – 6 ) ( L = L 1 to L 4 , 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 ( L 3 ), [Zn 4 (dipp) 4 ( L 3 ) 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 ( L 5 ) was investigated as the spacer. A slow reaction of 1 b with L 5 leads to the isolation of a 2D‐boxed‐sheet coordination polymer [Zn 4 (dipp) 4 ( L 5 ) 2 ] n ( 7 ). Selective formation of 3D‐framework 5′ from L 3 and the 2D‐framework 7 from L 5 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.