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Oddziaływania elektronowe w dwucentrowych kompleksach nitrozylowych molibdenu

Włodarczyk A., Romańczyk P.

Wiadomości Chemiczne

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2008

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[Z] 62, 3-4

187-208

EN

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].

2

The Mixed-Valence Rhenium(IV, V) Complexes

Banaś B., Nahorska M., Tomkiewicz A., Kłak J., Cyfert M., Mroziński J.

Polish Journal of Chemistry

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2006

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Vol. 80, nr 10

1663-1676

EN

Reaction of K4[Re2OCl10]with oxidizing agents in hydrochloric acid produced binuclear compounds: Cs3[Re2OCl10] 1, (Ph4As)3[Re2OCl10] 2, (ChinH)3[Re2OCl10] 3. These complexes had been characterized by kinetic and magnetic investigations. The low-temperature magnetic susceptibility measurements have revealed, that Cs3[Re2OCl10] complex is antiferromagnets, with Néel temperature at 10 K. The temperature dependence of the magnetic moment for 2 and 3 complexes indicates the existence of a magnetically isolated exchange-coupled dimer. In the electronic spectra, the intensive band at 20150 cm–1 is associatedwith the presence of the two different oxidation states. In agreementwith the evidence from the oxidation of oxochlororhenate ion and the disproportionation in solution, it is proposed that the compound should be considered as a Re(IV)–Re(V) mixed-valence system.

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An Anionic Moiety, MCl2- 4 (M=copper, zinc, cadmium and mercury) Stabilized by Bis(diethylenetriamine)copper(II) Cation

Siddiqi K., Rafat F., Siddiqi M., Lutfullah, Chebude Y.

Polish Journal of Chemistry

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2004

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Vol.78 /nr 11-12

2047-2053

EN

Bimetallic complexes of the type [Cu(dien)2][MCl4], where M = Cu(II), Zn(II), Cd(II) and Hg(II), were prepared by reacting bis(diethylenetriamine)copper(II) dichloride with copper, zinc, cadmium and mercury dichlorides in ethanol. They have been characterized by elemental analyses, IR, electronic and EPR spectra, magnetic moment, TGAand conductivity measurements. Electrical conductivity of all the complexes indicated them to be 1:1 electrolyte in DMF and that the copper(II) ion is paramagnetic, maintaining its octahedral geometry, while metal ions in the anionic moiety of the complexes achieve their usual tetrahedral environment. An augmented magnetic moment has been observed in the [Cu(dien)2][CuCl4] complex, which is attributed to the ferromagnetic effect. From the EPR spectra, the Cu-Cu distance (rjk) has been found to be larger in [Cu(dien)2][CdCl4] than in [Cu(dien)2][CuCl4]. The TGAof [Cu(dien)2][CuCl4] showed the decomposition of various fragments between 226 to 1000 graduate C.

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Bimetallic complexes with macrocyclic ligands. Variation of magnetic exchange interactions in some heteronuclear thiocyanato-bridged compounds

Tomkiewicz A., Kłak J., Mroziński M.

Materials Science Poland

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2004

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Vol. 22, No. 3

252--263

EN

A series of heterobinuclear, thiocyanato-bridged complexes of macrocyclic ligands of copper(II) and nickel(II) have been characterized by variable-temperature magnetic susceptibility (1.72-300 K). The complexes have the following composition: (CuL1)3[Fe(NCS)6]2ź3H2O (1), (CuL1)[Ni(NCS)6]ź2H2O (2), (CuL1)[Co(NCS)4]ź3H2O (3), where L1 is 5,12-dimethyl-[14]-1,4,8,11-tetraazacyclotetradeca-4,11-diene and (NiL2)3[Fe(NCS)6]2ź2H2O (4), (NiL2)[Co(NCS)4]ź3H2O (5), (NiL2)2[Cr(NCS)6] ClO4 (6), where L2 is 5,7,12,14-tetramethyl-[14]-1,4,8,11-tetraazacyclotetradeca-4,11-diene. The results indicate that all of them behave as weakly interacting magnets.