We discuss the physical criteria that have been proposed as a measure of the strength of a chemical bond. Critical examination of the strengths and weaknesses of the various quantities shows that the force constant is the most general measure for determining the strength of a chemical bond in molecules. The force constant of a bond AB is a direct indicator of the interatomic forces between the fragments A and B at the equilibrium distance, which is independent from the energies and electronic structures of the free species A and B. This is a great advantage compared to the use of energy differences for determining the bond strength, which are subject to the choice of the reference system that is often not uniquely defined. This is particularly evident when considering the strength of a chemical bond in strongly bonded but metastable species such as [O2]2+. The change in the electronic structure of the reference system obscures the intrinsic bond strength at equilibrium. Energy changes along the course of chemical reactions are elementary quantities in chemistry; they provide crucial information for the kinetics and thermodynamics of processors. However, they are not suitable as a measure of bond strength. The definition of local vibrational constants by Konkoli and Cremer eliminates the coupling of the stretching vibration with other vibrational modes, which makes it possible to use force constants as direct measure for bond strength also in larger molecules.

The double-tartaric bridging Tm-substituted POM derivative [N(CH3)4]6K3H7[Tm(C4H2O6)(α-PW11O39)]2·27H2O (1) was successfully synthesized and well characterized by various physico-chemical analyses. Furthermore, the mixed Dy3+/Tm3+ ion-based POM derivatives [N(CH3)4]6K3H7[DyxTm1-x(C4H2O6)(α-PW11O39)]2·27H2O (3-8) were first synthesized and confirmed by PXRD and IR spectra, indicating compounds 3-8 are isomorphic with 1. The detailed analyses of Ln-O-W bond angle and coordinated aqua ligands around emitting Ln3+ ions have revealed that the mentioned negative factors do not effectively affect the luminescence of emitting Ln3+ ions in 1-8. Investigations of PL emissions reveal that 3-8 can display color-tunable PL properties, emitting color from blue to white to yellow. The study of time-resolved emission spectroscopy of 6 indicates the energy can transfer from the LMCT excited state of POM fragments to Tm3+ and/or Dy3+ ions. Furthermore, the decreased luminescent lifetime of Tm3+ ions in 3-8 reasonably verifies the energy transfer from Tm3+ to Dy3+ ions to efficiently facilitate emissions of the Dy3+ centre.

Carbones are divalent carbon(0) species that contain two lone pairs of electrons. Herein, we have prepared the first known stable and isolable free bis‐(carbone) pincer framework with a well‐defined solid‐state structure. This bis‐(carbone) ligand is an effective scaffold for forming monometallic (Ni and Pd) and trinuclear heterometallic complexes with Au−Pd−Au, Au−Ni−Au, and Cu−Ni−Cu configurations. Sophisticated quantum‐theoretical analyses found that the metal–metal interactions are too weak to play a significant role in upholding these multi‐metallic configurations; rather, the four lone pairs of electrons within the bis‐(carbone) framework are the main contributors to the stability of the complexes.

Three isostructural lanthanide-containing polyoxometalates with 2D network architectures were successfully obtained under hydrothermal conditions.

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