Triazole ligands

Free carbenes based on 1,2,4-triazole are not as numerous as those based on imidazole (70ZN(B)1421, 95AGE1021, 97JA6668, 98JA9100). The carbene complex 169 (Ar = Ph, p-Tol) is prepared by the [3 + 2] cycloaddition route from [W(CO)j(C+=NC-HCOOEt)]- and aryldiazonium (930M3241). Oxidative decomplexation causes tautomerization of the 1,2,4-triazole ligand, the products being 170 (Ar= Ph, i-Tol). 

Somewhat unusual pressure dependence of the nature of the spin transition curve has been found for chain-like SCO systems containing substituted bridging triazole ligands [163, 164]. Although the transition is displaced to higher temperatures with increase in pressure, the shape of the transition curve, unusually, is effectively constant, i.e. there is no significant change in the hysteresis width and the transition remains virtually complete. This has been taken to indicate that the cooperativity associated with the transitions in these and related systems is confined within the iron(II) triazole chains. 

The N-l coordination mode has been found in bidimensional- [3] and in tridimensional materials [4] derived from 4,4 -bis-1,2,4-triazole, as well as in mononuclear compounds of bidentate 1,2,4-triazole ligands in which the N-4 atom is protected from coordination by a non-coordinating substituent, as in 4-amino-3,5-bis(pyridin-2-yl)-l,2,4-triazole [5-8], 4-p-methylphenyl-3,5-bis(pyridin-2-yl)-1,2,4-triazole [9] and 4-ra-methylphenyl-3,5-bis(pyridin-2-yl)-l,2,4-triazole [9]. 

The N-4 coordination towards Fe(II) has been found in mononuclear Fe(II) spin crossover compounds containing bidentate 1,2,4-triazole ligands [10-13], as well as tridentate ligands bearing no substituent at N-4 of the... 

The N-2, N-4 bridging coordination mode has not (yet) been observed in Fe(II) spin crossover compounds, whereas the N-l, N-2 bridging mode has been confirmed by X-ray structure determinations of oligomeric and polymeric Fe(II) spin crossover materials. Depending on the nature of the substituted 1,2,4-triazole ligand and the presence of potentially coordinating an-... 

In the crystal structure of [Fe3(etrz)6(H20)6](CF3S03)6 (etrz = 4-ethyl-1,2,4-triazole) the central Fe(II) ion is surrounded by six triazole ligands thus establishing an FeN6 chromophore. These triazole ligands are Nl,N2-... 

The frequent occurrence of thiocyanate in spin cross-over complexes is documented, in Section 5.4.1.4 above and in connection with diimine and with triazole ligands in Sections 5.4.3.5.9 and 5.4.3.6.3 below, while complex formation with iron(III) appears in Section 5.4.5.1.4. 

Figure 7 Example of a structural unit with three bridging 4-substituted triazole ligands, as found in many dinuclear and...

The coordination of indazolium ligands, as present in KP1019, appears beneficial for transferrin binding, compared to analogous complexes with imidazole or triazole ligands [102], as these ligands are better accommodated into the iron binding sites [97]. 

The few known triazole (17) compounds are of different type. MnS04 forms a mono species under conditions where Ni forms a tris, and this has a monomeric structure95 [Mn(S04)(H20)L]. On the other hand Mn(NCS)2 forms a polymeric Mn(NCS)2 2L species, in which the polymerization occurs through the triazole ligand (N-2 and N-4) bridging trans Mn(NCS)2 units.96 The other known triazole compound is Mn2(NCS)4(4-Me-triazole)5 which has97 the dimeric structure (19)... 

M3(detrH)6(NCS)4F2 (H20)2], which has also been structurally characterised. This complex can also be prepared from MF2, detrH and [M(NCS)2] [58], This same preparative method has also been used with a variety of substitued triazole ligands to yield complexes of the form [M3L4F2(NCS)4(H20).Y] (M = Co, Ni) [59]. 

Sutter, J.P., Kahn, M.L., Golhen, S. et al. (1998) Synthesis and magnetic behavior of rare-earth complexes with N,0-chelating nitronyl nitroxide triazole ligands example of a [Gd organic radical 2] compound with an 5=9/2 ground state. Chemistry - A European Journal, 4, 571-576. 

A triazole ligand, (28), leads to asymmetric coordination modes, giving inequivalent metal centers in homobimetallic complexes.94 Complexes of Ru,Os exhibit efficient energy transfer mediated by the triazole ring. Benzimidazole-based bridging ligands like 2,2 -bibenzimidazolate... 

Seredyuk et al. used a two-step procedure to obtain metallomesogens with a synchronous spin transition and a solid-to-mesophase transition. They started with the selection of an iron(II) complex with triazole ligands... 

Figure 2.65 Mesogenic triazole ligand forming complexes of the type [Fe(L)2](4-...

The synthesis of low-dimensional solids has become more important than ever before, both to chemists and physicists. In the catenation of metal ions, the catenating blocks are usually polynucleating ligands. The 1,2,4-triazole ligand acts in most of its metal complexes as a 1,2-bicoordinating ligand. In this type of coordination, linear polynuclear complexes are formed. 

The 1,2,4-triazole ligand (0.1 mole, 6.91 g) in 50 mL water is added to nickel(II) nitrate (0.05 mole, 14.54 g of the hexahydrate) dissolved in 50 mL water, whereupon the solution turns dark blue. Then, ammonium thiocyanate (0.1 mole, 7.61 g) in 25 mL water is added. Any turbidity is removed by filtration. Upon standing for several days, purple crystals of a-[Ni(NCS)2(trz)2] are formed. The crystal size depends on the concentration of reactants and the temperature, and may be up to 0.2 mm long. The product is recovered by filtration, washed with water and dried under vacuum. The yield is about 14 g (89%). 

The use of Tapy (l-(2-pyridyl)-l,2,3-triazole) ligand bearing long allqrl chains demonstrates an impressive enhancement of the luminescent properties of the rhenium complexes in aqueous medium relative to the parent Pyta complex." ... 

Each Cd " " ion shows an octahedral geometry and is surrounded by four nitrogen atoms from the pyridine and triazole ligands and by two oxygen atoms from the monodentate nitrate ligand and a methanol ligand. This structure can be seen as a one-dimensional polymeric chain [18]. 

Mahmoudi G, Morsali A. Crystal-to-crystal transformation an Hgll metal-organic polymer constructed with a triazole ligand. Z Anorg Allg Chem 2009 2697-700. 

Fu S, Zhang GX, Han ZB. Synthesis, structure, and photoluminescence of a 3D zinc(II) coordination polymer with tris(2-carboxyethyl)-isocyanurate and 1,2,4-triazole ligands. Z Anorg Allg Chem 2011 637(14-15) 2153-6. 

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