L-Leucine derived ligand (H2LL-leu), KOH, and Ni(II) salt in 2:21 ratio self-assembled into a rather large (similar to 13 angstrom) supramolecular assembly with the formula [K{Ni(HLL-leu)(2)}3](+) (1), Structural characterization showed three [Ni(HLL-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(HLL-leu)(2)}(3)](+), where M' is either K+ or Na+ and M is either Cu(II) or Ni(II); [Na{Ni(HLL-leu)(2)}(3)]ClO4 (2), [Na{Ni(HLL-leu)(2)}(3)]OTf (3), [K{Cu(HLL-leu)(2)}(3)]ClO4 (4), [Na{Cu(HLL-leu)(2)}(3)]ClO4 (5), [K{Cu(HLL-leu)(2)}(3)]NO3 (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(HLL-leu)(2)] and M', in stronger H-bonding methanol. The dissociation can be reversed upon addition of excess KNO3/NaNO3 salt. Structural characterization of [Cu(HLL-leu)(2)(MeCN)] (7) along with its transformation to [K{Cu(HLL-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(HLL-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 similar to 70 nm, thereby providing an indirect way of distinguishing K+ and Na+, none of which have spectroscopic signature in the visible range.