Synthesis, Structure, and Ligand Redistribution Equilibria of Mixed Ligand Complexes of the Heavier Group 2 Elements Containing Pyrazolato andβ‐Diketiminato Ligands

Pyrazoles and pyrazolides-flexible synthons in self-assembly

This Perspective summarises the chemistry of the pyrazole ring, and reviews the metal coordination modes adopted by 1H-pyrazoles and their anions. Pyrazolide anions are probably the most versatile ligands in coordination chemistry, with 20 different terminal or bridging coordination modes having been identified so far. Metal cluster compounds supported by pyrazolido ligation are surveyed, concentrating on those reported during the past ten years. Highlights include the wide structural diversity in apparently simple main group pyrazolides; luminescence and charge-transfer complexes in coinage metal pyrazolide clusters; the use of robust metal pyrazolide clusters to construct liquid crystals, supramolecular materials and metal-organic frameworks; and supramolecular complexes formed by pyrazolide-supported metallacrowns.

Role of Donor and Secondary Interactions in the Structures and Thermal Properties of Alkaline-Earth and Rare-Earth Metal Pyrazolates

The addition of neutral coligands to reduce the aggregation and improve the volatility of potential heavy alkaline-earth metal chemical vapor deposition (CVD) precursors has typically resulted in liberation of the coligand upon heating. A new series of dinuclear alkaline-earth and rare-earth metal pyrazolates, bis[bis(3,5-di-tert-butylpyrazolato)(tetrahydrofuran)calcium] (1), bis[bis(3,5-di-tert-butylpyrazolato)(tetrahydrofuran)strontium] (2), and bis[bis(3,5-di-tert-butylpyrazolato)bis(tetrahydrofuran)barium] (3), have been obtained from our previous donor-free oligonuclear complexes [{M(3,5-tBu2pz)2}n] (5, M = Ca, n = 3; 6, M = Sr, n = 4; 7, M = Ba, n = 6) by treatment with tetrahydrofuran (THF). Compounds 1-3, as well as the europium analogue bis[bis(3,5-di-tert-butylpyrazolato)(tetrahydrofuran)europium(II)] (4), can also be prepared by direct reaction of the metals and pyrazole in THF and anhydrous liquid ammonia. Recrystallization from hexane led to single crystals of 2-4, while the powder diffraction pattern of 1 revealed it to be isostructural with the previously published bis[bis(3,5-di-tert-butylpyrazolato)(tetrahydrofuran)ytterbium(II)] (8), providing important insight into differences and similarities between the two groups of metals. Detailed structural analysis of the compounds reveals secondary interactions including pi-bonding and agostic interactions, which are considered essential in stabilizing the metal complexes. The direct comparison of structural features and thermal properties (as evaluated by thermogravimetric analysis and sublimation studies) of the donor-free oligonuclear and the donor-containing dinuclear species offers a better understanding of the role of donors and secondary interactions.

Film growth precursor development for metal nitrides. Synthesis, structure, and volatility of molybdenum(vi) and tungsten(vi) complexes containing bis(imido)metal fragments and various nitrogen donor ligands

The molybdenum and tungsten complexes W2(NtBu)4(pz)4(pzH).(C6H14)0.5 (pz = pyrazolate), M(NtBu)2(Me2pz)2(Me2pzH)2 (Me2pz = 3,5-dimethylpyrazolate), M(NtBu)2(tBu2pz)2 (tBu2pz = 3,5-di-tert-butylpyrazolate), M2(NtBu)4(Me2pz)2Cl2, W(NtBu)2(C2N3(iPr)2)2py2, M(NtBu)2-(CN4CF3)2py2, and W(NtBu)2(PhNNNPh)2 were prepared by various synthetic routes from the starting materials Mo(NtBu)2Cl2, W(NtBu)2(NHtBu)2, and W(NtBu)2Cl2py2. These new complexes were characterized by spectral and analytical methods and by X-ray crystal structure determinations. The volatilities and thermal stabilities were evaluated to determine the potential of the new complexes for use in thin film growth of metal nitride films. Mo(NtBu)2(tBu2pz)2 and W(NtBu)2(tBu2pz)2 were found to have the optimum combination of volatility and thermal stability for application in atomic layer deposition thin film growth procedures.