New zinc complexes (LOMe)ZnCl2 (1) and (LOH)ZnCl2(2) of the heteroscorpionate ligands 1-[(3,5-di-tert-butyl-2- methoxyphenyl)(3,5-dimethyl-pyrazol-1-yl)methyl)]-3,5-dimethyl-pyrazole (LOMe) and 2,4-di-tert-butyl-6-[bis(3,5- dimethyl-pyrazol-1-yl)methyl]phenol (LOH) have been synthesized. The X-ray molecular structure of 2 was reported and compared with the one of the iron(II) complex (LOH)FeI2 (3). The complexes 2-3 adopt a tetrahedral structure in the solid state in which the LOH ligand is κ2 -coordinated to the metal via the imino nitrogens of the two pyrazolyl rings. The hydroxyl phenyl group is not coordinated to the metal but found to be involved in an intermolecular hydrogen bond. The solution structures of 1 and 2 are consistent with this tetrahedral CS symmetric geometry. Dilution and 1H-1H Nuclear Overhauser Effect Spectroscopy (NOESY) experiments revealed that the free ligands LOMe and LOH are involved in intra- and intermolecular hydrogen bonding interactions. Coordination of LOMe and LOH to ZnCl2 was investigated by NMR titrationmethods. Association constants (Ka) of (8.6(0.4)x10*2M-1 and (7.8(0.3)x10*2M-1were obtained in methanol/water solutions (95:5) for LOMe and LOH, respectively. Coordination of bis(3,5-dimethyl-pyrazol-1-yl)methane (bpm) ligand to ZnCl2 is weaker, as evidenced by the lower value of the association constant(5.3 ( 0.3) x 10*2M-1. When bpm was added to solutions of 1 or 2, an equilibrium shifted toward the (bmp)ZnCl2species was observed. The thermodynamic parameters for this reaction were determined by VT NMR analysis. The optical properties of the ligands (LOMe, LOH) and of the corresponding zinc complexes 1 and 2 were also investigated by means of UV-vis and fluorescence spectroscopy to assess the potential use of these ligands as fluorescent sensors for Zn2þ detection.
New Zinc Complexes bearing K2-Heteroscorpionate Ligands: Influence of Second-Sphere Bonding Interactions on Reactivity and Properties
BERTOLASI, Valerio;
2009
Abstract
New zinc complexes (LOMe)ZnCl2 (1) and (LOH)ZnCl2(2) of the heteroscorpionate ligands 1-[(3,5-di-tert-butyl-2- methoxyphenyl)(3,5-dimethyl-pyrazol-1-yl)methyl)]-3,5-dimethyl-pyrazole (LOMe) and 2,4-di-tert-butyl-6-[bis(3,5- dimethyl-pyrazol-1-yl)methyl]phenol (LOH) have been synthesized. The X-ray molecular structure of 2 was reported and compared with the one of the iron(II) complex (LOH)FeI2 (3). The complexes 2-3 adopt a tetrahedral structure in the solid state in which the LOH ligand is κ2 -coordinated to the metal via the imino nitrogens of the two pyrazolyl rings. The hydroxyl phenyl group is not coordinated to the metal but found to be involved in an intermolecular hydrogen bond. The solution structures of 1 and 2 are consistent with this tetrahedral CS symmetric geometry. Dilution and 1H-1H Nuclear Overhauser Effect Spectroscopy (NOESY) experiments revealed that the free ligands LOMe and LOH are involved in intra- and intermolecular hydrogen bonding interactions. Coordination of LOMe and LOH to ZnCl2 was investigated by NMR titrationmethods. Association constants (Ka) of (8.6(0.4)x10*2M-1 and (7.8(0.3)x10*2M-1were obtained in methanol/water solutions (95:5) for LOMe and LOH, respectively. Coordination of bis(3,5-dimethyl-pyrazol-1-yl)methane (bpm) ligand to ZnCl2 is weaker, as evidenced by the lower value of the association constant(5.3 ( 0.3) x 10*2M-1. When bpm was added to solutions of 1 or 2, an equilibrium shifted toward the (bmp)ZnCl2species was observed. The thermodynamic parameters for this reaction were determined by VT NMR analysis. The optical properties of the ligands (LOMe, LOH) and of the corresponding zinc complexes 1 and 2 were also investigated by means of UV-vis and fluorescence spectroscopy to assess the potential use of these ligands as fluorescent sensors for Zn2þ detection.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
