Chiral Metal Phosphonates With Tunable Structures And Properties

Chirality is essential in life,pharmaceutical industry and materials science.Chiral coordination compounds have received increasing attentions in recent years owing to their potential applications in chiral catalysis,chiral separation,chiral recognition,and multifunctional materials etc.Metal phosphonates are a class of important inorganic-organic hybrid materials which show high thermal and chemical stabilities and have potential applications in sorption,ion exchange,sensors and nonlinear optics.However,homochiral metal phosphonate complexes are rather limited in number,and the research in this field is still in the initial stage.This thesis work focuses on the assembly of chiral metal phosphonates and the illustration of their structural-property relationships.The achievements are obtained as follows:1.Homochiral metal phosphonates based on((1-phenylethyl)amino)methylphos-phonic acidBased on(S)-and(R)-((1-phenylethyl)amino)methylphosphonic acid(pempH2),we succeeded in isolating three new homochiral metal phosphonates with nanotubular structures,namely,(S)-and(R)-Mn(pemp)(H2O)2(S-1 and R-1),(S)-and(R)-Fe(pemp)(H2O)2(S-2 and R-2),(S)-and(R)-Cd(pemp)(H2O)2(S-3 and R-3).The luminescent and magnetic properties have been studied.2.Racemic cobalt phosphonates based on 2-phenyl-2-((phosphonomethyl)amino)acetic acid(ppaH3)and 3-phenyl-3-((phosphonomethyl)amino)propanoic acid(3-ppapH3)Based on racemic phosphonate ligands 2-phenyl-2-((phosphonomethyl)amino)acetic acid(ppaH3)and 3-phenyl-3-((phosphonomethyl)amino)propanoic acid(3-ppapH3)and incorporating flexible bridging ligands 1,2-or 1,3-or 1,4-bis((1H-imidazol-1-yl)meth-yl)benzene)(bix),we obtained four racemic cobalt phosphonates namely Co3(ppa)2(1,2-bix)2·4H2O(4),CO3(3-ppap)2(1,4-bix)3(H2O)4-4H2O(5),Co3(3-ppap)2(1,3-bix)3(H2O)4·5H2O(6)and Co3(3-ppap)2(1,2-bix)2(H2O)4-4H2O(7).In all cases,racemic chains composed of Co ions and O-P-O linkages are found.The main structural difference between 4 and 5-7 includes:1)compound 4 crystallizes in the monoclinic system space group C2,while compounds 5-7 crystallize in the monoclinic syGtem space group P21/c;2)the CoⅡ ions are either five-or four-coordinated within the chain in 4,while only six-coordinated in 5-7;3)the coligands bridge the neighboring Co atoms within the same chain to construct a chain structure in 4,while bridge the Co atoms from adjacent chains to form layer structures in 5-7.The magnetic studies reveal paramagnetic behaviors in all compounds.3.Chiral cobalt phosphonates based on 3-phenyl-2-((phosphonomethyl)amino)propanoic acid(2-ppapH3)We have successfully synthesized homochiral organophosphonic acids((S)-,(R)-3-phenyl-2-((phosphonomethyl)amino)propanoic acid(2-ppapH3)and its racemic analogue(Rac)-2-ppapH3.By incorporating rigid ancillary ligands 4,4’-bpy,five cobalt phosphonates are obtained,namely,(S)-,(R)-CO3(2-ppap)2(4,4’-bpy)2(H2O)2·4H2O(S-8,R-8),(Rac)-CO3(2-ppap)2(4,4’-bpy)2(H2O)2·4H2O(Rac-8),(S)-,(R)-Co3(2-ppap)2(4,4’-bpy)2(H2O)2·3H2O(S-9,R-9).Compounds S-8 and R-8,S-9 and R-9 are two pairs of enantiomers,respectively.Compound Rac-8 is a racemate and has the same topology with compounds 8.All contain chains composed of Co ions and O-P-O linkages.Compounds 8 and 9 are catenation isomers,which formation is controlled solely by the pH of the reaction mixtures.While the formation of isomeric compounds 8 and Rac-8 is controlled purely by the chirality of the phosphonate ligand.Magnetic studies reveal that compounds S-8、S-9 and Rac-8 show paramagnetic behaviors.But the magnetic behaviors of their dehydrated products are highly dependent on both the structures and chirality.Weak ferromagnetism is observed in the dehydrated compounds of S-8 and S-9,but not in Rac-8.Further,both the remnant magnetization and coercive field of the dehydrated compounds of S-8 and S-9 are different at same temperature.This work provides a new route to the magnetic modulation through chirality control,which has never been documented in the literature.If rigid 4,4’-bpy ligand is replaced by flexible bisimidazole ligands,we obtain nine cobalt phosphonates,namely,(S)-,(R)-Co3(2-ppap)2(1,4-bix)2(H2O)2·5H2O(S-10,R-10),(Rac)-CO3(2-ppap)2(1,4-bix)2(H2O)2·5H2O(Rac-10),(S)-,(R)-Co3(2-ppap)2(1,3-bix)2(S-11,R-11),(Rac)-CO3(2-ppap)2(1,3-bix)2(Rac-11),(S)-,(R)-Co6(2-ppap)4(1,2-bix)4·5H2O(S-12,R-12),and(Rac)-Co3(2-ppap)2(1,2-bix)2(H2O)2-2H2O(Rac-12).Compounds S-10 and R-10,S-11 and R-11,S-12 and R-12 are three pairs of enantiomers,respectively.Compounds Rac-10,Rac-11,Rac-12 are all racemates.These complexes also contain chains composed of Co ions and O-P-O linkages.But the coordination modes of the bridging ligands are quite different.In chiral compounds 10,1,4-bix bridges the Co atoms from neighboring chains to form layer structures.In chiral compounds 11,1,3-bix bridges the Co atoms from the same chain to form chain structures.In chiral compounds 12,1,2-bix links the Co atoms within the chain and between the chains forming different type of chain structures.The racemic compounds Rac-10 and Rac-11 possess identical structures with compounds 10 and 11,respectively.While the structure of compound Rac-12 is different from that of 12,where 1,2-bix only bridges the Co atoms between the chains.If the coligands are 1,4-bis((1H-1,2,4-triazol-1-yl)methyl)benzene(1,4-btix)or 1,2-bis((1 H-benzo[d]imidazol-1-yl)methyl)benzene(1,2-bbix),four new cobalt phosphonates can be obtained:(R)-CO3(2-ppap)2(1,4-btix)3·8H2O(R-13),(Rac)-Co3(2-ppap)2(1,4-btix)3·8H2O(Rac-13),(Rac)-Co3(ppap)2(1,4-btix)2(H2O)2·4H2O(Rac-14),(Rac)-CO2(2-ppapH)2(1,2-bbix)2-2H2O(Rac-15).The structures of chiral compound R-13 and racemic compound Rac-13 are identical,where inorganic chains composed of Co ions and O-P-O linkages are cross-linked by the 1,4-btix coligands resulting in a three-dimensional open framework structure.Racemic compound Rac-14 shows a layer structure in which the inorganic chains are bridged by 1,4-btix coligands.The structure of racemic compound Rac-15 is different from others.It shows a dimeric structure with the presence of π-π interactions between the dimmers.4.Chiral phosphonic acid as induction agent for the homochiral crystallization of cobalt coordination polymersChiral induction is a powerful and economic method to obtain homochiral coordination polymers from achiral building blocks by using a chiral template,chiral solvent or chiral catalysis.So far,there are very few chiral induction agents reported in the literature.We use chiral 2-ppapH3 as the induction agent,and obtain a pair of homochiral one-dimensional helical Co complexes of 1,3-bis((1H-benzo[d]imidazol-1-yl)methyl)benzene(1,3-bbix),namely,(M)-and(P)-Co(SO4)(1,3-bbix)(H2O)3(16M and 16P).This is the first report of homochiral crystallization from achiral precursors using a phosphonic acid as chiral induction agent.Magnetic studies reveal that compound 16M shows field-induced slow magnetization relaxation at low temperature.The energy barrier Ueff=17.5 cm-1(τ0=5.0×10-6 s).As far as we are aware,homochiral one-dimensional helical cobalt complexes displaying single-ion magnet behavior has not been documented in the literature.