title: Sodium and potassium ion directed self-assembled multinuclear assembly of divalent nickel or copper and L-leucine derived ligand.
abstract: L-leucine derived ligand (H(2)L(L-leu)), KOH, and Ni(II) salt in 2:2:1 ratio self-assembled into a rather large (approximately 13 A) supramolecular assembly with the formula [K{Ni(HL(L-leu))(2)}(3)](+) (1). Structural characterization showed three [Ni(HL(L-leu))(2)] units encapsulated K(+) similar to organic crown ethers/cryptand. Substituting Ni(II) with Cu(II) and K(+) with Na(+) in the above reaction resulted in a set of structurally identical assemblies with the general formula [M'{M(HL(L-leu))(2)}(3)](+), where M' is either K(+) or Na(+) and M is either Cu(II) or Ni(II); [Na{Ni(HL(L-leu))(2)}(3)]ClO(4) (2), Na{Ni(HL(L-leu))(2)}(3)]OTf (3), [K{Cu(HL(L-leu))(2)}(3)]ClO(4) (4), [Na{Cu(HL(L-leu))(2)}(3)]ClO(4) (5), [K{Cu(HL(L-leu))(2)}(3)]NO(3) (6). Electrospray Ionization (ESI)-mass spectra of the assemblies in MeOH showed the retention of assemblies in solution. Visible spectroscopic studies showed retention of assembly 1 in N,N-dimethylformamide (DMF) which is stable even after the addition of 5 equiv of [18]-crown-6. The assemblies in 2-6 show various degrees of dissociation to [M(HL(L-leu))(2)] and M', in stronger H-bonding methanol. The dissociation can be reversed upon addition of excess KNO(3)/NaNO(3) salt. Structural characterization of [Cu(HL(L-leu))(2)(MeCN)] (7) along with its transformation to [K{Cu(HL(L-leu))(2)}(3)](+) in the presence of K(+) salt demonstrated that the assembly formation proceeds through an alkali metal ion induced ligand reorientation within the [Cu(HL(L-leu))(2)] units which is further stabilized by six strong H-bonds holding the assembly. Interestingly, visible spectra of 1 and 2 shows that minor structural changes caused by replacing K(+) with Na(+) is sufficient to shift the d-d transition of Ni(II) by approximately 70 nm, thereby providing an indirect way of distinguishing K(+) and Na(+), none of which have spectroscopic signature in the visible range.
authors.affiliation: Department of Chemistry, Indian Institute of Technology Guwahati, North Guwahati 781039, Assam, India.
authors.forename: Mrigendra
authors.initials: M
authors.lastname: Dubey
authors.forename: Rik Rani
authors.initials: RR
authors.lastname: Koner
authors.forename: Manabendra
authors.initials: M
authors.lastname: Ray
mesh_terms: D002384:Catalysis; D003300:Copper / Q000737:chemistry*; D004563:Electrochemistry; D004578:Electron Spin Resonance Spectroscopy; D006843:Hydrocarbons, Chlorinated / Q000737:chemistry; D007477:Ions; D007930:Leucine / Q000737:chemistry*; D008024:Ligands; D008280:Magnetics; D008956:Models, Chemical; D015394:Molecular Structure; D009532:Nickel / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry; D012964:Sodium / Q000737:chemistry*; D013440:Sulfides / Q000737:chemistry
chemical_list: D006843:Hydrocarbons, Chlorinated; D007477:Ions; D008024:Ligands; D013440:Sulfides; D003300:Copper; D009532:Nickel; C007792:Fumigant 93; D012964:Sodium; D007930:Leucine; D010100:Oxygen