Chameleon Complexes

Because complexes usually arrive at their particular three-dimensional shape because it is the thermodynamically most stable form we tend to expect that they cannot change this outcome for the particular set of ligands they carry - each time they are made, the same result is achieved. While this is dominantly the case, it should be remembered that the thermodynamic stability relates to a particular set of conditions such as temperature, solvent and counter ions or electrolyte. Change the conditions and the system may be perturbed enough to undergo a physical change. Some changes may be readily reversible, so that reversing the change allows the complex to revert to its original form - genuine chameleon-like behaviour. The most obvious example of this is where a change in conditions creates a change in geometry. We have already noted that for some coordination numbers two different shapes may be similar in stability; providing the barrier to conversion between them is not too great, then interconversion may occur as a result of, for example, changing the temperature. The tetrahedral/square planar interconversion shown in Figure 4.12 is an example of this. Of course conversion from one isomer to another irreversibly to achieve the more thermodynamically stable form is common, and we shall deal with this later in this chapter.

The tendency to show flexibility in shape varies with coordination number because ligand-ligand repulsion energy differences between various shapes vary, as do the heights of energy barriers in reaching transition intermediates. As a consequence five- seven- eight- and nine-coordination tend to be substantially less rigid than four- and six-coordination and display more examples of chameleon-like behaviour. For example, not only is the ligand-ligand repulsion energy difference between the trigonal bipyramidal and square pyramidal geometries close to zero and definitely much less (perhaps as much as 50-fold) than between the two common four- and six-coordination shapes but also the transition states for rearrangement are less disfavoured so five-coordination tends to be less rigid.

اخر الاخبار

اخبار العتبة العباسية المقدسة

طوال الشهر الفضيل.. قسم الشؤون الخدمية يقدم أكثر من 42 ألف صندوق ماء للزائرين

بمشاركة 142 منتسبًا.. قسم الشؤون الدينية يختتم دورته الفقهية التطويرية السادسة

قسم بين الحرمين: قدمنا أكثر من 50 ألف وجبة إفطار للزائرين خلال شهر رمضان المبارك

المجمع العلمي يختتم نشاطاته القرآنية الرمضانية في المثنى

المزيد

الآخبار الصحية

كوب قبل النوم.. مشروب طبيعي يحارب الأرق

دون أدوية.. طريقة طبيعية لخفض ضغط الدم بفعالية مذهلة

المعكرونة ليست عدوك.. كيف تصبح جزءا من وجبة صحية متوازنة؟

دراسة: تناول القهوة يوميا يخفض خطر الإصابة بالاضطرابات النفسية

المزيد

الآخبار التكنلوجية

علماء روس يخططون لبناء منشأة للكشف عن المادة المظلمة

ثاني أكسيد الكربون ليس تهديدا للمناخ فقط.. بل لصحة الإنسان أيضا!

ديدان الأرض تكشف تلوث التربة بالمعادن الثقيلة

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

المزيد

مواضيع ذات صلة

Constitutional (Structural) Isomerism

Isomerism– Real 3D Effects

Moulding a Relationship - Ligand Influences

Metallic Genetics– Metal Ion Influences

Higher Coordination Numbers (ML7 to ML9)

Six Coordination (ML6)

Five Coordination (ML5)

Four Coordination (ML4)

Three Coordination (ML3)

Two Coordination (ML2)

Complex Lifetimes– Together Forever

?Preferences– Do You Like What I Like