More Teeth Stronger Bite - Polydentates

As a general observation the more donor atoms by which a molecule is bound to a metal ion the stronger will be the assembly. There is basic common sense in this, of course, since more donors bound means more coordinate bonds linking the ligand to the metal ion. To separate metal and ligand all of these bonds would need to be broken, which one would obviously anticipate costing more energy than breaking just a single bond to separate a metal ion from a monodentate ligand. A case of more is better, or greed is good. There is a conventional nomenclature to identify the number of bonds formed between a ligand and a central metal ion shown in Table 2.1. Here denticity defines the number of bound donor groups; this can equal the number of potential donor groups available (as in examples in the table) or be a lesser number if not all groups available are coordinated. See Appendix 1 for some other notes on polydenticity.

Table 2.1 identifies molecules that can bind at up to six coordination sites. This is by no means the limit ,  as inherently a molecule (such as a peptide polymer) may offer a vast number of potential donors. It is not uncommon for polydentate ligands to use only some and not all of their donors in forming complexes; this may be driven by the relative location of the potential donors on the ligand (and the overall shape and folding of the ligand), which affects their capacity to all bind at once, and the number of donors, as more may be offered than can be accommodated around the metal ion. As an example, a ligand like -OOC-CH₂-NH-CH₂-COO- has one amine and two carboxylate groups, all of which are capable of coordination. However, it may bind through one, two or all three of these donors acting in turn, as a mono- di- and tri-dentate ligand. Where more are available than required the set that eventually bind are usually those that produce the thermodynamically most stable assembly. Some molecules may easily accommodate more than one metal ion; a polymer with an array of donors would be an obvious example with different parts of the chain binding to different metal ions - we shall look at this prospect soon.

Table 2.1 Naming of different numbers of donor groups bound to a single metal ion with examples of typical simple linear ligands of each class.

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

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

Metals in the Natural World