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首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >Quantifying the relative contribution of hydrogen bonding and hydrophobic environments,and coordinating groups,in the zinc(II)-water acidity by synthetic modelling chemistry
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Quantifying the relative contribution of hydrogen bonding and hydrophobic environments,and coordinating groups,in the zinc(II)-water acidity by synthetic modelling chemistry

机译：通过合成模型化学定量分析氢键和疏水环境以及配位基团对锌（II）-水酸度的相对贡献

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Ligands derived from the tripodal N_4 ligand tris(pyridylmethyl)amine ((pyCH_2)_3N,tpa) of general formula (6-RNHpyCH_2),,N(CH_2py)_(3-n) (R=H,n=1-3 L~(1-3); R=neopentyl,n=1-3 L'~(1-3)) were used to elucidate and quantify the magnitude of the effects exerted by hydrogen bonding and hydrophobic environments in the zinc-water acidity of their complexes.The pK_a of the zinc-bound water molecule of [(L~(1-3))Zn(OH_2)]~(2+) 1-3 and [(L'~(1-3))Zn(OH_2)]~(2+) l'-3' was determined by potentiometric pH titrations in water (1-3) or water-ethanol (1:1) (l'-3').The zinc(II) water acidity gradually increases as the number of-NH_2 hydrogen bonding groups adjacent to the water molecule increases.Thus,the zinc-bound water of [(L~3)Zn(OH_2)]~(2+) and [(tpa)Zn(OH_2)]~(2+) deprotonate with pK_a values of 6.0 and 8.0,respectively.The pK_a of the water molecule,however,is only raised from 8.0 in [(tpa)Zn(OH_2)]~(2+) to 9.1 in [(bpg)Zn(OH_2)]~+ (bpa=(pyCH_2)_2N(CH_2COO~-)).Moreover,the acidity of the zinc-bound water of several of the five-coordinate zinc(n) complexes with the hydrogen bonding groups is greater than that of four-coordinate [((12)aneN3)Zn(OH2)]2+(pA:a=7.0).This result shows that the magnitude of the effect exerted by the hydrogen bonding groups can be larger than that induced by changing one neutral by one anionic ligand,and/or even by changing the coordination number of the zinc(II) centre.The X-ray structure of [(L'~2)Zn(OH)]ClO_4 2' and [(L'~3)Zn(OH)]C1O_4(center dot)CH_3CN 3'(center dot)CH_3CN is reported,and show the neopentylamino groups forming N-H…O hydrogen bonds with the zinc-bound hydroxide.Although l'-3',which have hydrogen bonding and hydrophobic groups,have a zinc-bound water more acidic than [(tpa)Zn(OH_2)]~(2+),their pK_a is not always lower than that of 1-3.This result suggests that a hydrogen bonding microenvironment may be more effective than a hydrophobic one to increase the zinc-water acidity.
机译：源自通式（6-RNHpyCH_2）的三脚架N_4配体三（吡啶甲基）胺（（pyCH_2）_3N，tpa）的配体，N（CH_2py）_（3-n）（R = H，n = 1-3 L〜（1-3）; R = neopentyl，n = 1-3 L'〜（1-3））用来阐明和量化氢键和疏水环境对锌-水酸度的影响程度[（L〜（1-3））Zn（OH_2）]〜（2+）1-3和[（L'〜（1-3））Zn的锌结合水分子的pK_a （OH_2）]〜（2+）l'-3'通过电位滴定法在水（1-3）或水-乙醇（1：1）（l'-3'）中进行测定。随着与水分子相邻的-NH_2氢键基团数目的增加，酸度逐渐增加。因此，[（L〜3）Zn（OH_2）]〜（2+）和[（tpa）Zn（ OH_2）]〜（2+）分别去质子化，pK_a值为6.0和8.0。然而，水分子的pK_a仅从[（tpa）Zn（OH_2）]〜（2+）中的8.0升高到9.1。在[（bpg）Zn（OH_2）]〜+（bpa =（pyCH_2）_2N（CH_2COO〜-））中。具有氢键基团的五配位锌（n）配合物中的几种的水合价大于四配位[（（12）aneN3）Zn（OH2）] 2+（pA：a = 7.0）的水。结果表明，氢键基团所产生的作用强度可能大于通过一种阴离子配体改变一种中性物和/或什至通过改变锌（II）中心的配位数所引起的作用强度。报道了[（L'〜2）Zn（OH）] ClO_4 2'和[（L'〜3）Zn（OH）] C1O_4（中心点）CH_3CN 3'（中心点）CH_3CN的结构，并显示了新戊胺基与氢键结合形成NH…O氢键的基团。虽然具有氢键和疏水基团的l'-3'具有比[[tpa）Zn（OH_2）]〜（2 +），它们的pK_a并不总是低于1-3。这一结果表明，氢键键合微环境可能比疏水键合微环境更有效地增加锌-水的酸度。

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