A group of copper complexes supported by polydentate pyridylamide ligands H 2 bpda and H 2 ppda were synthesized and characterized. The two Cu(II) dimers [Cu II 2 (Hbpda) 2 (ClO 4 ) 2 ] (1) and [Cu II 2 (ppda) 2 (DMF) 2 ] (2) were constructed by using neutral ligands to react with Cu(II) salts. Although the dimers showed similar structural features, the second-sphere interactions affect the structures differently. With the application of Et 3 N, the tetranuclear cluster (HNEt 3 )-[Cu II 4 (bpda) 2 (μ 3 -OH) 2 (ClO 4 )(DMF) 3 ](ClO 4 ) 2 (3) and hexanuclear cluster (HNEt 3 ) 2 [Cu II 6 (ppda) 6 (H 2 O) 2 (CH 3 OH) 2 ](ClO 4 ) 2 (4) were prepared under similar reaction conditions. The symmetrical and unsymmetrical arrangement of the ligand donors in ligands H 2 bpda and H 2 ppda led to the dramatic conformation difference of the two Cu(II) complexes. As part of our effort to explore mixed-valence copper chemistry, the triple-decker pentanuclear cluster [Cu II 3 Cu I 2 (bpda) 3 (μ 3 -O)] ( 5) was prepared. XPS examination demonstrated the localized mixed-valence properties of complex 5. Magnetic studies of the clusters with EPR evidence showed either weak ferromagnetic or antiferromagnetic interactions among copper centers. Due to the trigonal-planar conformation of the trinuclear Cu(II) motif with the μ 3 -O center, complex 5 exhibits geometric spin frustration and engages in antisymmetric exchange interactions. DFT calculations were also performed to better interpret spectroscopic evidence and understand the electronic structures, especially the mixed-valence nature of complex 5.

The nature of donor−acceptor interactions is important for the understanding of dative bonding and can provide vital insights into many chemical processes. Here, we have performed a computational study to elucidate substantial differences between different types of dative interactions. For this purpose, a data set of 20 molecular complexes stabilized by dative bonds was developed (DAT20). A benchmark study that considers many popular density functionals with respect to accurate quantum chemical interaction energies and geometries revealed two different trends between the complexes of DAT20. This behavior was further explored by means of frontier molecular orbitals, extendedtransition-state natural orbitals for chemical valence (ETS-NOCV), and natural energy decomposition analysis (NEDA). These methods revealed the extent of the forward and backdonation between the donor and acceptor molecules and how they influence the total interaction energies and molecular geometries. A new classification of dative bonds is suggested.

High-valent Fe(IV)-oxo intermediates, found in enzyme active sites, are excellent targets for biomimetic design of molecular catalysts for C-H bond activation. C-H bonds in inert aliphatic hydrocarbons, such as methane,...

We describe the preparation of the cis-bis­(η1,η2-2,2-dimethylpent-4-en-1-yl)­rhodate­(I) anion, cis-[Rh­(CH2CMe2CH2CHCH2)2]−, and the interaction of this species with Li+ both in solution and in the solid state. For the lithium­(diethyl ether) salt [Li­(Et2O)]­[Rh­(CH2CMe2CH2CHCH2)2], VT-NMR and 1H­{7Li} NOE NMR studies in toluene-d 8 show that the Li+ cation is in close proximity to the d z 2 orbital of rhodium. In the solid-state structure of the lithium­(12-crown-4) salt [Li­(12-crown-4)2]­[Li­{Rh­(CH2CMe2CH2CHCH2)2}2], one lithium atom is surrounded by two [Rh­(CH2CMe2CH2CHCH2)2]− anions, and in this assembly there are two unusually short Rh–Li distances of 2.48 Å. DFT calculations, natural energy decomposition, and ETS-NOCV analysis suggest that there is a weak dative interaction between the 4d z 2 orbitals on the Rh centers and the 2p z orbital of the Li+ cation. The charge-transfer term between Rh and Li+ contributes only about the 1/5 of the total interaction energy, however, and the principal driving force for the proximity of Rh and Li in compounds 1 and 2 is that Li+ is electrostatically attracted to negative charges on the dialkylrhodiate anions.

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