Structural trends

Key points: The 4d- and 5d-series elements often exhibit higher coordination numbers than their 3d-series congeners; compounds of d-metals in high oxidation states tend to have covalent structures.

We might expect the ionic radii of d-metal ions to follow the same pattern as atomic radii and decrease across each period. However, in addition to this general trend, there are some subtle effects on the size of the ions caused by the order in which. Figure 19.6 shows the variation in radius of the M2 ions for six-coordinate complexes of the 3d-series metals. To understand the two trends shown in the illustration we need to know that three of the 3d orbitals point between the ligands and that the remaining two point directly at them (this feature is explained more fully in Section 20.1). For the so-called ‘low-spin complexes’, in which electrons first individually occupy the three 3d orbitals that point between the ligands, there is a general decrease in radius across the series up to the d6 ion Fe²⁺. After Fe²⁺, the additional electrons occupy the two d orbitals that point towards the ligands, which they repel slightly and thus result in an effective increase in radius. The trend for the so-called ‘high-spin complexes’, in which the electrons occupy all five 3d orbitals singly before pairing with any already present, is more complicated. Initially, at Ti²⁺ (d²) and V²⁺ (d³), the electrons occupy the three 3d orbitals that point between the ligands and the radius decreases. The next two electrons occupy the two orbitals that point at the ligands, and the radii increase accordingly. Then the sequence starts again at Fe2 (d6), as the additional electrons pair with those already present, first in the ‘non-repelling’ set of three orbitals and then, finally, in the two ‘repelling’ orbitals.

As might be anticipated from consideration of atomic and ionic radii, the 4d- and 5d series elements often have higher coordination numbers than their smaller 3d-series co geners. Table 19.4 illustrates this trend for the fluorido and cyanido complexes of the early d metals. Note that with the small F ligand, these 3d-series metals tend to form six coordinate complexes but that the larger 4d- and 5d-series metals in the same oxidation state tend to form seven-, eight-, and nine-coordinate complexes. The octacyanidomoly- bdate complex, [Mo(CN)₈]^3- , illustrates the tendency towards high coordination numbers with compact ligands. The same complex is readily reduced electrochemically or chemically without change of coordination number:

Structural changes also result from changes in metal oxidation state. Compounds of d metals in low oxidation states often exist as ionic solids, whereas compounds of d metals in high oxidation states tend to take on covalent character: compare OsO₂ , which is an ionic solid with the rutile structure, and OsO₄ , which is a covalent molecular species (Section 19.8). We discussed the effect in Section 1.9e.

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اخبار العتبة العباسية المقدسة

جامعة العميد تنظم ورشة تدريبية عن برنامج منصة التعليم العالي

قسم الشؤون الفكرية ينظم برنامجًا دينيًّا لكشافة الكفيل في النجف الأشرف

العتبة العباسية المقدسة تقدم دعوة لجامعتي الكوفة والطوسي للمشاركة في مشروعها القرآني الخاص بطلبة الجامعات

قسم الشؤون الفكرية يصدر مجموعة جديدة من الإصدارات المعرفية والثقافية

المزيد

الآخبار الصحية

كيف يمكن لحفنة من الجوز أن تؤثر على نومك وتركيزك؟

دراسة: كوب ميلك شيك واحد قد يكون "قنبلة دماغية"

هل يعد "الباراسيتامول" خيارا آمنا للنساء الحوامل؟

دراسة تكشف الرابط بين العلاقات العاطفية والرضا عن الحياة

المزيد

الآخبار التكنلوجية

كارثة صامتة.. "الهواء الملوث" يسرق نور عيون الأطفال

دراسة: رصد أول دليل على وجود "إشعاع هوكينغ"

رسالة بلغة لا تعرفها؟.. "واتساب" يترجمها لك فورا

"إنستغرام".. ميزة جديدة لكشف "الكذب في العمر"

المزيد

مواضيع ذات صلة

Thermochemical correlations

Magnetic measurements

Octahedral complexes

Sulfide complexes

Disulfides

Polyoxometallates

Mononuclear oxido complexes

Metal oxides

Oxidation states down a group

Intermediate oxidation states in the 4d and 5d series

Intermediate oxidation states in the 3d series

High oxidation states