Syntheses,Structures And Magnetic Properties Of Metal Phosphonates Or Vanadates Embedding Mn^? Schiff Base Building Units

Single molecule magnets(SMMs)and single chain magnets(SCMs)have received increasing attentions in recent years due to their potential applications in high-density information storage and quantum computation.Mn? Schiff Base compounds are good building blocks in constructing SMMs and SCMs.On the other hand,the phosphonates and vanadates with the strong coordination capabilities towards metal ions are promising in constructing new compounds with interesting magnetic properties.With the aim of exploring new single molecule magnets and single chain magnets,this thesis work is focused on the assembly of metal phosphonates or vanadates embedding Mn? Schiff Base building units which show novel architectures and interesting magnetic properties.The main achievements are listed as follows:1.Zero-dimensional Mn? Schiff Base phosphonates(1)Based on Mn(salen)+ unit,hexanuclear clusters[Mn6(salen)6(C6H5PO3)2(H2O)2](C104)2·2H2O(1)and[Mn6(salen)6(2-FC6H4PO3)2(H2O)2](ClO4)2·3H2O(2),as well as trinuclear clusters[Mn3(salen)3(4-FC6H4PO3)]2(ClO4)2·2H2O(3)and[Mn3(salen)3(4-CH3C6H4P03)(CH30H)(H20)](Cl04)·H20(4)have been obtained successfully by reacting[Mn(salen)(H2O)]2(ClO4)2 and phosphonic acids in the presence of triethylamine.Compounds 1 and 2 consist of two triangular-shaped[Mn3PO3]units connected with two phenoxide oxygen atoms,while the independent triangular[Mn3PO3]units exist in 3 and 4.Magnetic measurements of 1-2 show that there are ferromagnetic interactions passing through phenolate bridges and antiferromagnetic interactions passing through O-P-O bridges,and they show single-molecule magnet behavior at low temperature.For compounds 3 and 4,antiferromagnetic interactions are mediated between the Mn? centers via the O-P-O bridges.(2)Based on Mn(5-Brsalen)+ unit,a dinuclear compound[Mn2(5,Brsalen)2(C10H7PO3)2]·CH3OH(5)and a hexanuclear cluster[Mn6(5-Brsalen)6(C10H7PO3)2(H2O)2](ClO4)2·7.6H2O(6)are obtained.Both show single molecule magnet behaviours at low temperature.Compounds 1-6 provide the first examples of metal phosphonate clusters embedding Mn? Schiff Base building units.2.One-dimensional Mn? Schiff base phosphonates(1)First examples of O-P-O bridged[Mn2(salen)2]2+ chain compounds,namely,[Mn2(salen)2(C6H9PO3H)](ClO4)(7),[Mn2(salen)2(2-FC6H4P03H)](Cl04)·1/2CH3OH(8),[Mn2(salen)2(C6H5P03H)](Cl04)(9),[Mn2(salen)2(4-FC6H4P03H)](C104)(10)and[Mn2(salen)2(C6H5PH02)](ClO4)(11)are synthesized.The phosphonate/phosphinite ligands adopt different coordination modes in 7-11,e.g.a syn-anti bidentate bridging mode in 7 and 8 while a syn-syn bidentate bridging mode in 9-11,which can be related to the weak C-H …? interactions between salen and the organic group of the phosphonate/phosphinite ligand.Such a difference causes a significant change in the Mn-O…O-Mn torsion angle over the O-P-O bridge,which are 100.8,96.6,0.8,1.9 and 9.5° for 7-11,respectively.Consequently,the antiferromagnetic exchange couplings mediated through the O-P-O pathway in 7 and 8 are extremely weak,and the overall magnetic behaviors are dominated by the Mn2(salen)2 moieties.Compound 7 shows a paramagnetic behavior because the short Mn?-O(axial)distances and large Mn-O(axial)-Mn angle within the dimer favor anti ferromagnetic interactions.The intra-dimer ferromagnetic coupling in compound 8 makes it a new example of single molecule magnets based on[Mn2(salen)2]2+dimers.In compounds 9-11,the antiferromagnetic interactions through the O-P-O bridges are much stronger than those in 7 and 8.Compounds 9-11 display coexistence of single chain magnet behavior with a spin canted structure and metamagnetism at low temperature.(2)Two couples of enantiomerically pure Mn? Schiff Base phosphonates are successfully synthesized by using chiral Mn? schiff base mononuclear precursors:[Mn?((R,R)-5-Brsalcy)]+/[Mn?((S,S)-5-Brsalcy)]+.Compounds[Mn((R,R)-5-Brsalcy)(2-FC6H4PO3H)]·3H2O(12)and[Mn((R,R)-5-Brsalcy)(4-CH3C6H4PO3H)]·CH3OH·H2O(14)[5-Brsalcy =N,N'-(1,2-cyclohexanediylethylene)bis(5-bromosalicylideneiminato)dianion]are isostructural and show similar one-dimensional chain structures where the Mn((R,R)-5-Brsalcy)+ species are bridged by O-P-O units.Compounds[Mn((S,S)-5-Brsalcy)(2-FC6H4PO3H)]·3H2O(13)and[Mn((S,S)-5-Brsalcy)(4-CH3C6H4PO3H)]·CH3OH·H2O(15)are(S,S)-enantiomers of 12 and 14,respectively.The four compounds are all optically active,exhibiting second harmonic generation responses 0.3 times that of urea.The magnetic measurements of 12 and 14 reveal that dominant anti ferromagnetic interactions are mediated between the Mn? centers.3.Two-dimensional Mn? Schiff base phosphonateThe first example of two-dimensional Mn? Schiff Base phosphonates,namely,[Mn4(salen)4(HO3PCH2C6H4CH2PO3H)](ClO4)2·2H2O(16)is obtained.The[HO3PCH2C6H4CH2PO3H]2-ligand adopts a tetradentate bridging mode,linking four[Mn2(salen)2]2+ moieties via phosphonate oxygen atoms into a 2D network structure.Magnetic measurements reveal that dominant ferromagnetic interactions are mediated between the Mn? centers and it shows the single molecule magnet behavior at low temperature.4.Three-dimensional Mn? Schiff base vanadateA novel[Mn?2(salen)2]2+ vanadate compound with formula[Mn6(salen)6(H2O)V4O12](ClO4)2·7H2O(17)is obtained,where the[Mn2(salen)2]2+dimers are covalently linked by the cyclic V4O124-cluster to form a three-dimensional open framework structure.Compound 17 is the first example of 3D polymers that embed dimeric Mn2(SB)2 building units.Moreover,it shows a SMM behavior at low temperature.