Structure and Dynamics of Dinuclear Zirconium(IV) Complexes

Abstract

We have determined by X-ray crystallography the structures of three dinuclear zirconium(IV) complexes containing the heptadentate ligand dhpta (where H(5)dhpta = 1,3-diamino-2-propanol-N,N,N',N'-tetraacetic acid, 1) and different countercations: K(2)[Zr(2)(dhpta)(2)].5H(2)O (2.5H(2)O), Na(2)[Zr(2)(dhpta)(2)].7H(2)O.C(2)H(5)OH (3.7H(2)O.C(2)H(5)OH), and Cs(2)[Zr(2)(dhpta)(2)].H(5)O(2).Cl.4H(2)O (4.H(5)O(2).Cl.4H(2)O). In the K(I) complex 2, crystallized from water, the two Zr(IV) ions are 3.5973(4) A apart and bridged via two alkoxo groups (average Zr-O 2.165 A). Each Zr(IV) is eight-coordinate and also bound to two N atoms (average Zr-N 2.448 A), and four carboxylate O atoms (average Zr-O 2.148 A). The two dhpta ligands in the dinuclear unit have different conformations. One face of the complex contains an array of 14 oxygen atoms and interacts strongly with the two K(I) ions, one of which is 6-coordinate, the other 8-coordinate, which are 3.922(4) A apart and bridged by a carboxylate O and by two water molecules. The structures of the dinuclear anion [Zr(2)(dhpta)(2)](2-) in the Na(I) complex 3 and in the Cs(I) complex 4 are essentially identical to that found in complex 2, although the alkali metal ions coordinate differently to the oxygen-rich face. All Zr(IV) ions have a distorted triangulated dodecahedral geometry. Although the crystal structure of complex 2 does not indicate the presence of acidic protons, in 4 an [H(5)O(2)](+) unit is strongly H-bonded to an oxygen atom of a coordinated carboxylate group. 1D and 2D (1)H and (13)C NMR spectroscopic and potentiometric studies reveal two deprotonations with pK(a) values of 9.0 and 10.0. At low pH, two carboxylate groups appear to undergo protonation accompanied by chelate ring-opening, and the complex exhibits dynamic fluxional behavior in which the two magnetically nonequivalent dhpta ligands exchange at a rate of 11 s(-1) at pH 3.30, 298 K, as determined from 2D EXSY NMR studies. Ligand interchange is not observed at high pH (>11). The same crystals of complex 2 were obtained from solutions at pH 3 or 12. The dynamic configurational change is therefore mediated by the aqueous solvent.

Molecular and supramolecular ionic aggregates HxOyzin organic and organometallic crystalline hydrates

“…All OÁ Á ÁO distances in the two isomers of H 11 O 5 + are as expected for charge-assisted and normal hydrogen bonds: BEXFEQ ( Fig. 7a; Zhong et al, 2004) and IYEPEH ( Fig. 7b; Makha et al, 2004).…”

Selective formation of lanthanide(III) complexes with polyaminopolycarboxylate: Unprecedented tetranuclear neodymium(III) complex containing alkoxo and carboxylato bridges

“…Among them, 2-hydroxypropane-1, 3-diamine-N,N,N 0 ,N 0 -tetraacetic acid (H 4 dptaOH) is recognized as a potentially heptadentate dinucleating ligand. When early transition metal or lanthanide (Ln) metal ions, whose ionic radii are relatively large, were used, homoleptic complexes were obtained [2][3][4][5]. Previously, we have reported the late Ln(III) dinuclear complexes, Na 4 [Ln 2 (l-dptaO) 2 ] (Ln = Ho III , Yb III ) [5], which contain octacoordinate Ln(III) ions.…”

New structures of hydronium cation clusters

“…The existence of new hydronium ion structures is a matter of some interest. These include the hydronium cations (H 11 O 5 + ) of two totally different geometrical structures, one BEXFEQ [6] (acyclic) and one IYEPEH [7] (cyclic). By calculating their molecular energies, the issue of which of the two structures is most stable has been settled.…”

“…Two of these hydronium cations shared the same composition (H 11 O 5 + ) but they have totally different geometrical structures, one acyclic and the other cyclic. In the Cambridge Structural Database [2–5] 1 they are indexed as BEXFEQ [6] (acyclic) and IYEPEH [7] (cyclic). In as much as the X-ray diffraction data which gave rise to these structures was considered to be reliable, an obvious question to ask is “which of the two as described by the crystallographic coordinates is more stable”.…”