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Kinetical and mechanical aspects of metal helicates Ana-Marija Bartolincic(Mia Vikki,AMBLab)Content IntroductionSpecifity of metal helicatesMechanical aspects of metal helicates Kinetical aspects of metal helicatesCharacterisation of metal helicates using analytical methodsUsage ConclusionReferences

IntroductionTerm called halicate have been deployed for the first time by Lehn et al.in 1987 to describe double stranded polymetal helix and defining a metal contained helixThe word helix comes from greece word meaning helicoidal, turned, strand,coil, and added ate at the end to actually define :guest host complexes between organisied receptors and metal ions IntroductionThe term helicates also include specific bonding in types of compounds like:Coronates (macrocylic compounds or macrocyclic compounds of Na/K group)Cryptates (macropolycyclic complexes with one or more inclusional metal ions)

Introduction

Picture 1.Example of metal helicate IntroductionThere are four main concepts in supramolecular chemistry to involve :A)molecular recognition representing selective interaction between two/three componentsB)selforganisation-connected with systems which can spontaniously generate well defined supramolecular arhitecture from specific part of initial components under specific conditions IntroductionC)selfarrangement-responds to basic level in selforganisation process D)supramolecular programing responds to involving orders in component of any device if a device is a metal complex Specifity of metal helicates Selfarrangement have been additionaly described by Lawrence,Jaing and LevettStoddard et al. have defined three most important facts of metal helicates :a)helicity in metal helicatesb)physical and chemical parametres which control termodynamic selfarrangement which lead to creating helicatesc)structural characterisation of those gigantic compounds Specifity of metal helicatesThere are some main examples of those compounds-pseudotetrahedral compounds with two bidentatic ligands type AB which are coordinated on metal center (Picture 2.a) and 2.b))**galium atom in picture is just for presentation, does not represent galium metal complex Specifity of metal helicates

Picture 2.a) and 2.b.)A and B represents different ligands Mechanical aspects of metal helicates final definitionMetal helicates is a supramolecular complex made by one or two covalent organic straind wraped around complex and coordinated series of ions who have their own position in structure of helicoidal axes Mechanical aspects of metal helicates Mechanical aspects of metal helicates needs these conditions to be aquired:A)one or more acyclic ligands have been wraped and coordinated around cations or anions with forming coordinative bond(coordinative bond-old chemical definiton for chemical interaction)Mechanical aspects of metal helicates B) a helicate consists of minimal two ions and the number n is a number determing nucleicity and makes a polynuclear oligomere

Mechanical aspects of metal helicates structural effectsMetal cations are used for snythesis of metal helicates cause they possess specific properties needed for supramolecular structures:A)specific coordinative properties, coordination numbers,stereochemical preferences depended by size, charge and electronic structure Mechanical aspects of metal helicates structural effectsB)wide spread of bond with ligands and kinetical stability , for example:lowspin Ru(II) and Os(II) have d8 configuration which makes them suitable for making inert and strong covalent bonds while labile and weak electrostatic bonds are made by Na(I) complexesc)variable affinity for different bond units-ligands Mechanical aspects of metal helicates structural effectsd)specific magnetic , electronic and spectroscopic properties which can be found in final product Mechanical aspects of metal helicates structural effectsLigand properties are important :Homotopic helicates-made from coordinated ligand strands which possess sequence of similar bonding unit along with the strand with similar intrinsic informations Heterotopic helicates-coordinated ligands with different bonding units giving directionality within the strand possess two forms :Head-to-head(HH) or Head-to-tail(HT)

Mechanical aspects of metal helicates structural effectsPicture 3.Homotopic helicates saturated(middle) and unsaturated (below)(ACD chemsketch)

Mechanical aspects of metal helicates structural effects

Picture 3.Heterotopic helicates saturated(middle) and unsaturated (below)(ACD chemsketch)Mechanical aspects of metal helicates structural effectsSaturated homotopic helicate-example(ACD Chemsketch)

Kinetical aspects of metal helicates Reactions between metal helicates and ligand strands match into a category which Lindsey called as `hard selforganised` in which final metal helicate responds to termodinamically most stable product The final product requires several conditions including bond making and breaking Kinetical aspects of metal helicates Bond making and breaking have to be very fast in according to :A)explore potential energy of hypersurface of combining complex which lead to minimum of free energy (G)B)alow to reject `mistakes`which lead to local minimum energy which makes that easy to combine coordinative bonds instead of labile hydrogen bonds most favourable Kinetical aspects of metal helicates Secondary thermodynamic effects neccecery for fomation of helicates are:Alosteric effectsRegulatory effectsCooperativity effectsKinetical aspects of metal helicates lability vs.inert stateTo choose a metal center that will arrange in time depended chirality taking in mind water molecule supstitution reactions on metal center itself The measured reusults show that the reactions of racemisation was faster for ligand change on water metal complexes most common type:[M(OH2)m]n+

Kinetical aspects of metal helicates lability vs.inert stateWilliams et al. showed that coordination of chiral oxalate anion changes the helicity of isolated -cis-Co(R-picpn)Cl2]ClO4 complex into -cis form in hot water(Picture 4)Kinetical aspects of metal helicates lability vs.inert state

Picture 4.Helicate inversion with Co(II) complex through anion exchange Kinetical aspects of metal helicates lability vs.inert stateLabile metal helicates coordinated with achiral ligands show dynamic equilibrium between right(M mark) and left (P mark)handed (oriented) helical structuresThere are two approaches towards programing helical structure of labile metal helicatesKinetical aspects of metal helicates lability vs.inert stateThey are :A)`ligand chirality`-also defined as chirality of additional ligand which gives helicoidal geometry between two enantiomeric formsB)`complex helicity`-around metal center responsable for activating supramolecular helicity or coil(Picture 5)Kinetical aspects of metal helicates lability vs.inert state

Picture 5.On the left:`ligand chirality` and on right `complex helicity`(with permission of Kagakudojin,Kagaku,2004,59,70)

Kinetical aspects of metal helicates-choice of cations?The range of cations or anions capable coordinating metal center on the place organic ligand goes withing this sequence: NO3->Cl->Br->CF3SO3- >ClO4-PF6-BF4- , and sometimes we can found CF3SO3- to be bound with NO3- to metal center Higly symetrical ligands as flourides and hypochlorides which are often used as noncordinative ligands often produce amorfcicity inside helicate complex

Characterisation of helicates using analytical methods Its hard to find inner crystal structure of any helicate due to several reasons:Most of them are very labile(can`t make crystals without losing some ligand strands)Show great dynamics in solutionsCarrying positive or negative charge and sometimes very nonactive to form nucleus

UsageManipulation and investigation of their properties led to some advances in chemistry of materials and proved some physical fenomena in inorganic reaction mechanismsSelfrecognised and programmed supramolecular structures as LED and OLED(organic light emitting diodes)UsageTwodimensional inorganic latters,edges,intercoiled catenates and knotsAlosteric ionophores-metal organic complexes important for passive transport through intermembrane space

ConclusionAdvantages :Consistent with principles of supramolecular chemistryUsed for LED, OLED and other complex inorganic structuresDisadvantages:Lack of determing inner structure Restricting behaviour of ligands Sometimes very slow or imposibble synthesisReferencesConstable,E.C.,Chem.Ind.,1994,56Lawrence, D.S.,Jiang ,T.,Levett,M.,Chem.Rew.1995,95,2229Harris,C.M.,Mc Kenzie,E.D.,J.Chem.Soc.(A),1969,746Sanchez-Quesada,J.,Seel,C.,Prados,P.,de Mendoza,J.,Jour.of Am.Chem.Soc.,1996,118,277Mislow,K.,Chimia,1986,40,395Lindsey,J.S.,New.J.Chem.,1991,15,153Williams,A.F.,Piquet,C.Carina,R.in `Transition Metals in Supramolecular chemistry`, Khawer Academic Publishers,1994,p404Brewster,J.H.,Topp.Curr.Chem.,1974,47,29Piguet,C.,Bernardinelli,G.,Hopfgartner,G.,Chem.Rev.,1997,97,2005

ReferencesLehn,Jean-Marie.,Science,2002,295,2400Van der Sluis,P.,Hezemans,A.M.F.,Kroon,J.,J.Appl .Crystallogr.,1989,22,340,Chambers,J.A.,Goodwin,T.J.Mulqi,M.W.,Williams,P.A.,Inorg.Chim.Acta.,1983,75,241Biscarini,P.,Kuroda,R.,Inorg.Chim.Acta.,1988,154,209About me-Ana-Marija BartolincicFor more information look at my linked.in profileContact me through e-mail:anamarija.bartolincic@yahoo.comFaculty of Science-Zagreb, Croatia, section:Inorganic and Organic Chemistry ,-subsection:complex MOF(metal organic frameworks)and POC (porous organic cages)