Monomeric and dimeric nitrate lanthanide(III) and yttrium(III) coordination compounds of (2 + 2) imine macrocycle derived from 2,6-diformylpyridine and trans-1,2-diaminocyclopentane

Abstract

Monomeric nitrate coordination compounds [Ln(L1)](NO3)3·nH2O (Ln = Y(III), Tm(III), Yb(III) and Lu(III)); n = 0, 0.75 or 3)11For simplicity of description we included the Y(III) in the abbreviation of Ln(III), commonly reserved for lanthanide(III) ions. It is well known that although yttrium does not belong to the lanthanides, the ionic radius of the Y(III) cation is similar to ionic radii of lanthanide(III) cations. Y(III) coordination compounds resemble very much in their chemical properties those of the respective lanthanide(III) coordination compounds. of the chiral macrocyclic (2 + 2) imine L1 (L1RRRR, L1SSSS and/or L1rac), derived from enantiomerically pure or racemic trans-1,2-diaminocyclopentane (DACP) and 2,6-diformylpyridine (DFP), have been synthesized in the templated condensation of precursors in the presence of appropriate metal salts. From these monomers their homochiral μ-hydroxodimers [Ln2(L1)2(μ-OH)2](NO3)4·nH2O (Ln = Y(III), Tm(III), Yb(III) and Lu(III)); n = 4, 5 or 7) have been obtained and isolated by addition of NaOH to the respective monomeric form of coordination compound solution. All synthesized coordination compounds have been characterized by NMR spectroscopy, mass spectrometry, elemental analyses and/or circular dichroism (CD). 1H NMR signals of CDCl3/CD3OD solutions of the diamagnetic Y(III) and Lu(III) monomers have been assigned on the basis of their COSY and HMQC spectra, and for the remaining paramagnetic lanthanide coordination compounds (Tm(III) and Yb(III)) the signals were tentatively assigned on the basis of linewidths analyses. 1H NMR signals of D2O solutions of diamagnetic Y(III) and Lu(III) representatives of dimeric species have been established taking into account their COSY, HMQC, HMBC and NOESY spectra. The NOESY spectra confirm that the structure of the dimmers observed in solids is also maintained in a solution.The axial ligand exchange in all monomeric coordination compounds was investigated by 1H NMR titration experiments with acetate and chloride anions in organic solvents as well as with hydroxide anion in D2O. The formation of homochiral heterobimetallic μ-hydroxodimers [Ln’Ln”(L1)2(μ-OH)2](NO3)4 was investigated in a solution by mixing the solutions of two different [Ln’2(L1)2(μ-OH)2](NO3)4·nH2O and [Ln”2(L1)2(μ-OH)2](NO3)4·nH2O homochiral homobimetallic precursors. This experiment proves the chiral recognition between two macrocyclic units of the same chirality in a solution. The μ-hydroxodimers may convert with time to the corresponding peroxo-dimers of the general formula [Ln2(L1)2(μ-η2: η2-O2)](NO3)4.The X-ray crystal structures of the representative monomeric and dimeric coordination compounds [Yb(L1RRRR)(NO3)2]NO3, [Yb2(L1SSSS)2(OH)2(H2O)2](NO3)4·2MeOH·2H2O, [Yb2(L1RRRR)2(OH)2(H2O)2][Yb2(L1SSSS)2(OH)2(H2O)2](NO3)8·1.5MeOH·5H2O and [Y2(L1SSSS)2(O2)(NO3)2](NO3)2·2MeOH with enantiomerically pure or racemic ligand L1 have been determined. The structure of [Yb2(L1RRRR)2(OH)2(H2O)2][Yb2(L1SSSS)2(OH)2(H2O)2] (NO3)8·1.5MeOH·5H2O crystal confirms chiral recognition of macrocyclic units of the same chirality in solids.