Invited Review Thermochromism and Solvatochromism in Solution
The thermochromic behaviour of various coordination compounds in solution is discussed, with a special focus on cyclic diamine chelates. Thermally induced spin-crossover phenomena of iron(II) complexes are also considered. The solvatochromic behaviour of
- PDF / 1,742,175 Bytes
- 16 Pages / 595.276 x 790.866 pts Page_size
- 113 Downloads / 141 Views
Thermochromism and Solvatochromism in Solution Usama EI-Ayaan 1,2, Fumiko Murata2 , and Yutaka Fukuda2,* 1 2
Department of Chemistry, Faculty of Science, Mansoura University, Mansoura 35516, Egypt Department of Chemistry, Faculty of Science, Ochanomizu University, Tokyo 112-8610, Japan
Summary. The thermochromic behaviour of various coordination compounds in solution is discussed, with a special focus on cyclic diamine chelates. Thermally induced spin-crossover phenomena of iron(II) complexes are also considered. The solvatochromic behaviour of mixed-ligand complexes is presented in detail. Keywords. Thermochromism; Spin-crossover; Solvatochromism; Solvent effect; Magnetic properties.
Introduction
The colours of coordination compounds originate from (i) d-d transitions, (ii) CT transitions (ML- and LM-CT), (iii) intervalence transitions, and (iv) ligand 1T-1T* transitions. The change of chemical and physical conditions (temperature, pressure, solvent, etc.) strongly influences the colours of the complexes. Colour change induced by temperature is known as thermochromism. Solvatochromism is another property of many coordination compounds; in this case, colour change is a consequence of solvent polarity. Thermochromism
The term thermochromism is defined as the change of the colour of a substance, or a system of substances, when heated to a certain temperature. The change can be reversible, i.e. the original colour returns upon cooling, or irreversible. Thermochromism on thermally induced spin-crossover iron(II) complexes
Thermally induced spin-state transitions between the low-spin (LS) and the highspin (HS) states of transition metal complexes with d4 to d7 electronic configuration are observed when the ligand field splitting energy (~o = 10 Dq) is approximately
*
Corresponding author. E-mail: [email protected]
W. Linert (ed.), Highlights in Solute-Solvent Interactions © Springer-Verlag Wien 2002
44
U. El-Ayaan et al.
Fig. 1. High-spin and low-spin states in iron(II) compounds
outweighed by the spin-pairing energy P [1, 2]. In other words, a spin-crossover phenomenon is observed when the energy difference between the HS and LS states is of the order of kT (Fig. 1). In the course of such a spin-crossover, temperature dependent changes of the magnetic moment are observed. A thermally induced LS ~ HS transition is characterized by an x = f(T) curve, where x is the molar fraction of HS molecules and (1 - x) that of LS molecules. A method to obtain such a curve is to measure the temperature dependence of the magnetic susceptibility. XT is constant in the temperature range where all molecules are in the same spin state «(XT)LS and (XT)HS' respectively). Therefore, the x = f(T) curve can be deduced from the experimental XT = f(T) curve according to Eq. (1).
(1) Spin-crossover phenomena (S = 0 to S = 2 transitions) have been well documented for various iron (II) complexes [3, 4]. Among them, [Fe(phenh(NCSh]' [Fe(phenh(NCSeh]' and [Fe(bpyh(NCSh] have been studied using different experimental techniques. It sh
Data Loading...
