Structural Regulation And Reactivity Study Of Silver Alkynyl Clusters

Atomically precise coinage metal(Cu,Ag,and Au)nanoclusters are a novel class of emerging materials that bridge the gap between metal atoms and nanoparticles.These nanoclusters have designable structures and tunable properties,the acquisition of which is crucial for both basic and applied science.The rapid development of gold nanoclusters has laid a good foundation for the synthesis and functional development of silver nanoclusters.Studies on the preparation of silver nanoclusters and physicc chemical properties,accurately controlling the shape and size and determining the single crystal structures is of paramount importance.Exploring the assembly mechanism and establishing the structure-properties relationship are extremely challenging.Therefore,we selected alkynes as the main ligands and inorganic oxyanions,dithiophosphate,and carboxylic acid as the auxiliary ligands,and synthesized several series of novel silver clusters under the guidance of surface ligand engineering.In situ spectroscopy was used to investigate their reactivity,assembly,and transformation mechanisms.The contents of the thesis are as follows.Ⅰ.Silver cluster co-protected by inorganic and organic ligandsFor the first time,an atomically precise inorganic and organic ligands co-protected Ag48 cluster[Ag48(C≡CtBu)20(CrO4)7](Ag48)was prepared using an inorganic ligand modulation strategy.The pseudo-fivefold symmetric metal skeleton of Ag48 consists of an Ag23 cylinder and an Ag25 shell,forming an Ag23@Ag25 core-shell structure.The CrO42-serves three important funcations in the construction of silver nanoclusters:i)passivating the Ag23 kernel;ⅱ)connecting the kernel and shell;and iii)protecting the Ag25 shell.Electrospray ionization mass spectrometry(ESI-MS)and single crystal structure confirmed that Ag48 belongs to the 14e system,and its electronic structure and optical properties were further studied by theoretical calculation.In addition,Ag48 exhibits an emission peak at 420 nm in CH2Cl2 solution at 293 K,whereas the emission peak redshifts to 441 nm at 80 K.This work provides a new strategy for the construction of silver clusters by inorganic ligands and reveals the critical surface coordination chemistry of CrO42-shaping the structure of silver clusters.Ⅱ.Janus clusters:asymmetric assembly of silver alkynyl shells and polyoxometalatesAn asymmetric hybrid cluster with only ca.60%surface coverage,{[K(H2O)HP5W30O110]@Ag43(tBuC≡C)29(CN)(CH3CN)2(H2O)}·3CH3CN(Ag43)was prepared by using a high-symmetry Preyssler polyoxometalate(P5W30)and[tBuC≡CAg]n.The asymmetric Ag43 shell comprises two segments,Ag16(tBuC≡C)10 and Ag25(tBuC≡C)15,which are linked by a pair of Ag(tBuC≡C)2 units.The time-dependent ESI-MS indicates that tBuC≡CAg gradually increased to the surface of P5W30 during the formation of Ag43.The typical redox peaks of P5W30 and Ag(I)clusters can be detected in cyclic voltammetry because P5W30 is not completely covered by the Ag shell.The electrocatalytic efficiency of Ag43 for nitrite reduction is 5.6 times that of P5W30,indicating that the hybrid of POM and silver cluster has successfully realized the dual functionalization.In addition,crystalline Ag43 exhibits nearinfrared emission(λmax=689 nm)at 78 K.This work laid the foundation for the synthesis of new silver clusters protected by inorganic POM ligands.Ⅲ.Regulation of silver cluster cores by alkynyl ligands and their luminescence propertiesTwo core-shell silver nanoclusters,[Ag7S6@(MoO4)2@Ag48(pMePhC≡C)24(Ph2PS2)12]·3CF3SO3-4CH3OH·2H2O(Ag55)and[Ag6S6@(MoO4)2@Ag48(PhC≡C)24(Ph2PS2)12]·2CF3S≡3(Ag54)co-protected by dithiophosphate ligands were synthesized by regulating alkynyl ligands.Both have a similar Ag48 shell and peripheral ligand distribution but different silver cores(Ag7S6 vs.Ag6S6).Although no direct bonding between alkynes and silver core is observed,we propose that the ligand effect still exerts deep influences on the size and geometry of the silver core.At the same time,Ag55 exhibits a redshift(40 nm)of emission in CH2Cl2 solution than Ag54 at room temperature due to more and stronger argentophilic interactions.Interestingly,ESI-MS captured the ligand exchange process between Ag55 and cyclopropyl acetylene.The reactivity and the kinetic relationship of Ag55 have been established.This work not only provides a pair of comparable examples to understand the substitution group effect of protecting ligand on the core structures and properties but also enables the regulation of luminescence properties.Ⅳ.Structure and mechanism insights into the reactivity of silver alkynyl cluster induced with dicarboxylic acidsThe surface ligand exchange strategy was used to induce the structural transformation of flexible silver clusters.Herein,we have synthesized a flexible 54-nuclei silver cluster,[K@(CrO4)6@Ag54(tBuC≡C)24(NPrCOO)18]+(Ag54a)by employing tBuC≡C-and nPrCOOligands.The existence of weakly coordinated nPrCOO-enhances the reactivity of Ag54a,thus facilitating the dicarboxylic acid-induced structural transformation.X-ray structural analyses reveal that Ag54a transforms to Ag28 cluster-based 2D networks{[(CrO4)2@Ag28(tBuC≡C)16(nPrCOO)2(suc)3]·2CH3CN}n(Ag28a)and[(CrO4)2@Ag28(tBuC≡C)16(glu)4]n(Ag28b)induced by H2Suc(H2suc=succinic acid)and H2glu(H2glu=glutaric acid),respectively,whereas with H2pda(H2pda=2,2’-(1,2phenylene)diacetic acid)a discrete Ag28 cluster[(CrO4)2@Ag28(tBuC≡C)16(tPrCOO)4(pda)2]·2nC3H7COOH(Ag28c)is isolated.The "TandemEquilibrium-Induced-Transformation" mechanism for the structure evolution from Ag54a to Ag28a is established by time-dependent ESI-MS and UV-vis spectroscopy.The results provide a certain degree of controllable regulation of silver cluster structure,and provide a new insight into the mechanism of dicarboxylates-induced structural transformation from cluster to another or cluster-based metal-organic frameworks.