Wyniki wyszukiwania - BazTech

Ograniczanie wyników

1 Wiadomości Chemiczne

1 2008

Znaleziono wyników: 1

Liczba wyników na stronie

Wyniki wyszukiwania

Wyszukiwano:
w słowach kluczowych: electronic interactions

Sortuj według:

Ogranicz wyniki do:

Oddziaływania elektronowe w dwucentrowych kompleksach nitrozylowych molibdenu

Włodarczyk A., Romańczyk P.

Wiadomości Chemiczne

2008

[Z] 62, 3-4

187-208

Design and synthesis of redox active binuclear complexes in which metal centres are linked via bridging ligands enabling electronic and magnetic interactions between them are crucial for an understanding of key processes in chemistry and biology. In biological systems, such as proteins, electron transfer involves a charge transport over a considerable distance (>10 A*) [8-11,13-19]. On the other hand, long range electronic interactions are central in the development of potential elements for molecular electronics like molecule-sized wires, diodes, light activated switches, transistors (Fig. 1), logic gates etc. [1-7]. This article reviews some of the work performed in the area of bimetallic nitrosyl molybdenum complexes containing tris(3,5-dimethylpyrazol-1-yl)hydroborato ligand (Fig. 4). Numerous examples of mixed-valence species have been described, showing a wide range of behaviour from fully delocalized to valence-trapped systems of which electrochemical (voltammetry, Fig. 3), spectroscopic (EPR (Fig. 5), IR and UV-Vis/NIR spectroscopy) and magnetic susceptibility were studied. These results are summarised in Table 1. Many such complexes show exceptionally strong electrochemical (?Ef) and magnetic exchange interactions (J) between metal centres depending on the features of the bridging ligand such as length, degree of conjugation, dihedral angles between aromatic rings, substitution pattern, and symmetry [28, 41]. For example, in [{Mo(NO)(TpMe2)Cl}2{4,4'-bipy}] (Fig. 9) ?Ef equals 765 mV, being an order of magnitude greater when compared to the {Ru(NH3)5}2+/3+ analogue, and J = -33 cm-1 [43, 68, 69]. Using 3,3'-dimethyl-4,4'-bipy as a bridge forces a twist between the two pyridyl rings and decreases both ?Ef and J down to 380 mV and 3.5 cm-1, respectively [42, 71]. The introduction of a saturated section into the bridge, which breaks the conjugation, e.g. in 1,2-bis(4-pyridyl)ethane ligand, considerably decreases ?Ef (105 mV) but does not exclude electronic and magnetic through-bridge interactions [43]. Recently a series of bimetallic complexes based on {Mo(NO)(TpMe2)}2+ centres comprising n-alkanediolate bridges (Fig. 12) have been prepared. These species exhibited intermediate metal-metal interactions (310 mV in ethane-1,2-diolate) [54, 55] which prompted investigation of electronic interactions through saturated alkyl chains by DFT [64].