Sulfide complexes

Key point: Chelating polysulfide ligands are common in metal sulfur coordination compounds of the 4d- and 5d-series metals. The coordination chemistry of sulfur is quite different from that of oxygen. Much of this difference is connected with the ability of sulfur to catenate (form chains), the availability of low-lying empty 3d orbitals that allow an S atom to act as a π acceptor, and the preference of sulfur for metal centres that are not highly oxidizing (Section 16.11). Simple thiometallate complexes such as [MoS₄]^-2 can be synthesized easily by passing H₂S gas through a strongly basic aqueous solution of molybdate or tungstate ions:

These tetrathiometallate anions are building blocks for the synthesis of complexes con taining more metal atoms. For example, they will coordinate to many dipositive metal ions, such as Co²⁺ and Zn⁺2:

The polysulfide ions, such as S₂^2- and S₃ ^-2, which are formed by addition of elemental sulfur to a solution of ammonium sulfide, can also act as ligands. An example is [Mo₂(S₂)₆ ]^2- (11), which is formed from ammonium polysulfide and MoO₄^-2; it contains side-bonded S2 2 ligands. The larger polysulfides bond to metal atoms forming chelate rings, as in [MoS(S₄)₂ ]^-2 (12), which contains chelating S4 2 ligands. Clusters of Fe and S atoms (‘Fe S clusters’) are cofactors in many enzymes, including nitrogenase, which converts N2 to NH3 under ambient conditions (Chapter 15). Synthetic analogues such as the cubane shown in (13) have been prepared and characterized. The cubane contains Fe and S atoms on alternate corners, so each S atom bridges three Fe atoms; each of the Fe atoms has a thiolate group, RS, occupying a terminal position. These compounds can be obtained from simple starting materials in the absence of air using a polar aprotic solvent such as dimethylsulfoxide:

The HS ion provides the sulfide ligands for the cage, the RS ion serves as both a ligand and a reducing agent, and the CH₃O ion acts as a base. Addition of the bulky cation from (Et4N) Cl results in the formation of black crystals of (Et₄N)₂ [Fe₄S₄ (SR)₄]. The observation that this reaction is successful, in good yield, with many different R groups indicates that the Fe4 S4 cage is thermodynamically more stable than other possibilities. The cage under goes reversible one-electron reduction to [Fe₄S₄ (SR)₄]^3-, a reaction that is important in biological oxidation and reduction (Section 27.8).

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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

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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

Disulfides

Polyoxometallates

Mononuclear oxido complexes

Metal oxides

Structural trends

Oxidation states down a group

Intermediate oxidation states in the 4d and 5d series

Intermediate oxidation states in the 3d series

High oxidation states