β-Diketonate Coordination: Vibrational Properties, Electronic Structure, Molecular Topology, and Intramolecular Interactions. Beryllium(II), Copper(II), and Lead(II) as Study Cases

Nine metal complexes formed by three symmetric β-diketonates (viz., acetylacetonate (acac), 1,1,1,3,3,3-hexafluoro-acetylacetonate (hfac), and 2,2,6,6-tetramethylheptane-3,5-dionate (tmhd)) and three metal ions (with three different coordination geometries, viz., BeII - tetrahedral, CuII - square planar, and PbII - "swing" square pyramidal) were investigated. The study combines structural analyses, vibrational spectroscopic techniques, and quantum chemical calculations with the aim of bridging crystal structure, electronic structure, molecular topology, and far-infrared (FIR) spectroscopic characteristics. The effect of intramolecular interactions on the structural, electronic, and spectroscopic features is the center of this study. The crystal structure of Be(tmhd)2 is also reported and discussed for the first time. A complete review of the experimental IR spectra is offered; discrepancies in the assignments of some peaks are revealed among the published works. Anharmonic effects were considered for acac complexes; however, they were negligible for the FIR modes. A systematic comparison between computed and experimentally measured data allowed us to design an inexpensive, yet efficient computational protocol to investigate large polynuclear complexes.

Heterometallic Molecular Architectures Based on Fluorinated β-Diketone Ligands

This review summarizes the data on the synthesis of coordination compounds containing two or more different metal ions based on fluorinated β-diketonates. Heterometallic systems are of high interest in terms of their potential use in catalysis, medicine and diagnostics, as well as in the development of effective sensor devices and functional materials. Having a rich history in coordination chemistry, fluorinated β-diketones are well-known ligands generating a wide variety of heterometallic complexes. In this context, we focused on both the synthetic approaches to β-dicarbonyl ligands with additional coordination centers and their possible transformations in complexation reactions. The review describes bi- and polynuclear structures in which β-diketones are the key building blocks in the formation of a heterometallic framework, including the examples of both homo- and heteroleptic complexes.

Homo- and Hetero-Oligonuclear Complexes of Platinum Group Metals (PGM) Coordinated by Imine Schiff Base Ligands

Chemistry of Schiff base (SB) ligands began in 1864 due to the discovery made by Hugo Schiff (Schiff, H., Justus Liebigs Ann. der Chemie 1864, 131 (1), 118-119). However, there is still a vivid interest in coordination compounds based on imine ligands. The aim of this paper is to review the most recent concepts on construction of homo- and hetero-oligonuclear Schiff base coordination compounds narrowed down to the less frequently considered complexes of platinum group metals (PGM). The combination of SB and PGM in oligonuclear entities has several advantages over mononuclear or polynuclear species. Such complexes usually exhibit better electroluminescent, magnetic and/or catalytic properties than mononuclear ones due to intermetallic interactions and frequently have better solubility than polymers. Various construction strategies of oligodentate imine ligands for coordination of PGM are surveyed including simple imine ligands, non-innocent 1,2-diimines, chelating imine systems with additional N/O/S atoms, classic N2O2-compartmental Schiff bases and their modifications resulting in acyclic fused ligands, macrocycles such as calixsalens, metallohelical structures, nano-sized molecular wheels and hybrid materials incorporating mesoionic species. Co-crystallization and formation of metallophilic interactions to extend the mononuclear entities up to oligonuclear coordination species are also discussed.

Volatile heterometallics: structural diversity of Pd-Pb β-diketonates and correlation with thermal properties

Volatile heterobimetallics based on Pb(ii) hexafluoroacetylacetonate as a host material and a range of Pd(ii) complexes containing both various donor atoms and terminal substituents in the β-diketonate ligand have been studied to trace the influence of the nature of the initial monometallic complexes on the structure, composition and thermal properties of heterobimetallic compounds. The structural variety and stoichiometry of the heterobimetallic compounds are caused by various combinations of the competing donor-acceptor interactions between the constituting monometallic moieties. The major structure forming factor is the metallophilic interaction between Pd and Pb atoms resulting in polynuclear structures with a specific topology. The structural motif (discrete or polymeric) for the compounds significantly depends on the structure and composition of the initial monometallic complexes. The approach for explaining and predicting the thermal stability of these compounds is proposed by using their structural data and the results of quantum chemistry calculations.

Volatile Heterobimetallic Complexes from PdII and CuII β-Diketonates: Structure, Magnetic Anisotropy, and Thermal Properties Related to the Chemical Vapor Deposition of CuPd Thin Films

A novel approach for preparing volatile heterometallic complexes for use as precursors for the chemical vapor deposition of various materials is reported. New CuPd complexes based on β-diketonate units were prepared, and their structures and compositions were determined. [PdL₂ *CuL₂ ] (1) and [PdL₂ *Cu(tmhd)₂ ] (2) (L=2-methoxy-2,6,6-trimethylheptane-3,5-dionate; tmhd=2,2,6,6- tetramethylheptane-3,5-dionate) are 1D coordination polymers with alternating metal complexes, which are connected through weak interactions between the Cu atoms and the OCH₃ groups from the ligand of the Pd complexes. The volatility and thermal stability were studied using thermogravimetric and differential thermal analyses and mass spectrometry. Compound 1 vaporizes without decomposition into monometallic complexes. It exhibits magnetic anisotropy, which was revealed from the angular variations in the EPR spectrum of a single crystal. The vapor thermolysis process for 1 was investigated using mass spectrometry, allowing the process to be framed within the temperature range of 200-350 °C. The experimental data, supported by QTAIM calculations of the allowed intermolecular interactions, suggest that 1 likely exists in the gas phase as bimetallic molecules. Compound 1 proved to be suitable as a single-source precursor for the efficient preparation of CuPd alloy films with tunable Cu/Pd ratio. A possible mechanism for the film growth is proposed based on the reported data.