摘要:
IntroductionThe ability to predict and control the assembly of molecules and complexions into extended ordered networks is an important goal in crystal engineering.Even though there are many inherent difficulties with using comparativelyweak forces as primary synthetic tools, considerable progress has been madeduring the last decade.1In this context, theselectivity and directionality of the hydrogen bond have been instrumentalin the preparation of distinctive structural aggregates,2and the use of hydrogen bonding as a steering force has emerged as the mostimportant strategy in crystal engineering.3Despite recent advances, detailed control over the supramolecular assemblyof molecules remains an elusive goal, and much more work is required to increasethe choice of reliable building blocks of extended architectures held togetherby non-covalent forces.4The oxime functionality is well known in organic synthesis,5analytical chemistry,6and coordination chemistry,7–10yet it has remained relativelyunexplored as an intermolecular connector in crystal engineering.11However, recent work has shown how oxime pyridine derivatives can be utilizedin the assembly of a variety of coordination complexes into extended networks.12,13By itself, the oxime moiety can, in theabsence of other hydrogen bond donors/acceptors, generate several low-dimensionalnetworks through hydrogen bonds. Adjacent moieties can form a head-to-headR22(6) motif (resulting in discrete dimers), or a catemericmotif that can lead to either discrete multi-molecular rings or infinitechains,Scheme 1.Possible hydrogen bondmotifs with oxime functionalities.From a crystal engineering perspective, the oxime moiety could be particularlyappealing since it is electronically and sterically ‘tunable’;RandR′ can be modified to include a wide range of electrondonors/acceptors or ‘inert’ spacers, and these functional groupsare accessible through well-known synthetic methods.14If the oxime functionality is attached to a moiety that can act as coordinatingsite for a metal ion, then a potential ‘bridge’ between coordinationcomplexes and supramolecular assembly has been constructed,Scheme 2.Generic oxime-substitutedpyridine ligand for crystal engineering of coordination complexes.Previous data demonstrate that the oxime functionality does enable theassembly of silver(I) ionsviathe dimeric head-to-headinteraction to infinite silver(I) chains that are further propagatedinto 2D sheetsviaC–H⋯O hydrogen bonds,Fig. 1.Infinite cationic sheetin di(3-acetyloximepyridine)silver(I) hexafluorophosphate.The counter-ions are positioned between the cationic layers, and participatein weaker hydrogen bonds to the layer above and below. Structures of thistype demonstrate that supramolecular synthesis using the oxime functionalitycan provide predictable structural arrangements where coordination complexesare directed into ordered networks by relatively weak forces working in concert.As part of this process, it is necessary to (i) synthesize and characterizea range of new ligands and (ii) to determine their solid-state behaviorand hydrogen bond patterns in the absence of metal-ions. In this paperwe present the syntheses of five oxime-substituted pyridine ligands, andthe crystal structures of seven such compounds.
ISSN:1466-8033
DOI:10.1039/b006043g
出版商:RSC
年代:2000
数据来源: RSC