Metals in Molecules

Metals in the elemental form typically exhibit bright, shiny surfaces– what we tend to expect of a ‘metallic’ surface. In the atmosphere, rich with oxygen and usually containing water vapour these surfaces may be prone to attack, depending on the E0 value; this leads to the bright surface changing character as it becomes oxidized. Although a highly polished steel surface is attractive and valued, the same surface covered in an oxide layer (better known in this particular case as rust) is hardly a popular fashion statement. Yet it is the formation of rust which is perfectly natural, with the shiny metal surface the unnatural form that needs to be carefully and regularly maintained to retain its initial condition. What we are witnessing with rust formation is a chemical process governed by thermodynamics (attainment of an equilibrium defined by the stability of the reaction products compared to the reactants) and kinetics (the rate at which change, or the chemical reaction, proceeds to equilibrium under the conditions prevailing). While the outcome may not be aesthetically appealing (unless one wants to make a virtue of rusted steel as a ‘distressed’ surface with character), chemistry is not given to making allowances for the sake of style or commerce it is a demanding task to ‘turn off’ the natural chemistry of a system. Some metals, such as titanium, are less wilful than iron; they undergo surface oxidation, but form a tight monolayer of oxide that is difficult to penetrate and thus is resistant to further attack. Of course, were the metal ions that exist in the oxidized surface to undergo attack in a different way, through complexation by natural ligands and subsequent dissolution, fresh metal surface would be exposed and available for attack. Such a process, occurring over long periods, would suggest that free active metals would increasingly end up dissolved as their ions in the ocean, and this is clearly not so– most metal ion concentrations in the ocean are very low (apart from alkali metal ions, being 0.001ppm). In reality, because reactive elemental-state metals are made mainly through human action, the contribution to the biosphere even by reversion to ionic forms will be small. Most metals are locked up as ions in rocks– particularly as highly insoluble oxides, sulfides, sulfates or carbonates that will dissolve only with human interception, through reaction with strong acids or ligands. Even if they enter the biosphere as soluble complex ions, they are prone to chemistry that leads to re-precipitation. The classic example is dissolved iron(II), which readily undergoes aerial oxidation to Fe(III) and precipitation as a hydroxide, followed by dehydration to an oxide, all occurring below neutral pH. Thus in the laboratory we tend to meet almost all metals in a pure form as synthetic cationic salts of common anions. These tend to be halides or sulfates, and it is these metal salts, hydrated or anhydrous, that form the entry point to almost all of metal coordination chemistry. In nature, it is no accident that metal ions that are relatively common tend to find roles, mediated of course by their chemical and electrochemical properties. Thus iron is heavily usednot only because it is common,but also because it forms strong complexes with available biomolecules and has an Fe(II)/(III) redox couple that is accessible by biological oxidants and reductants and thus useful to drive some biochemical processes.

اخر الاخبار

اخبار العتبة العباسية المقدسة

متحف الكفيل يباشر صيانة المجموعة الرابعة من مقتنيات العتبة العسكرية المقدسة

ضمن برنامجها التبليغي اليومي.. شعبة الخطابة تنظم مجلسًا للوعظ والإرشاد

قسم الشؤون الفكرية يواصل إقامة مسابقة النور الزكي الرمضانية في ذي قار

المجمَع العلمي يواصل إقامة 18 ختمة قرآنية رمضانية في الديوانية

المزيد

الآخبار الصحية

دراسة: تناول القهوة يوميا يخفض خطر الإصابة بالاضطرابات النفسية

عرض شائع في الفم قد يكون مرتبطا بخطر الإصابة بأمراض خطيرة

نصائح عامة لاستخدام سماعات الرأس بأمان

تأثير اللياقة البدنية على الدماغ

المزيد

الآخبار التكنلوجية

ديدان الأرض تكشف تلوث التربة بالمعادن الثقيلة

خبير أرصاد جوية: ظاهرة النينيو القادمة قد تكون الأقوى خلال 10 سنوات

"ناسا" تكشف موعد إعادة إطلاق رحلتها المأهولة إلى القمر

علماء الجيولوجيا يفكون لغز الصدع العملاق تحت الماء في المحيط الأطلسي

المزيد

مواضيع ذات صلة

Meeting More Metals - Bridging Ligands

More Teeth Stronger Bite - Polydentates

Greed is Good– Polydentate Ligands The Simple Chelate

Monodentate Ligands– The Simple Type Basic Binders

Ligands with More Bite– Denticity

Different Tribes– Donor Group Variation

Do I Look Big on That?– Chelate Ring Size

Putting the Bite on Metals– Chelation

Making Attachments– Coordination

The Road Ahead

Natural or Made-to-Measure Complexes

Metals in Contrived Environments