The reaction of 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane (DAPTA) with metal salts of Cu or Na /Ni under mild conditions led to the oxidized phosphane derivative 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane-5-oxide (DAPTA=O) and to the first examples of metal complexes based on the DAPTA=O ligand, that is, [Cu (μ-CH COO) (κO-DAPTA=O)] (1) and [Na(1κOO';2κO-DAPTA=O)(MeOH)] (BPh ) (2). The catalytic activity of 1 was tested in the Henry reaction and for the aerobic 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO)-mediated oxidation of benzyl alcohol. Compound 1 was also evaluated as a model system for the catechol oxidase enzyme by using 3,5-di-tert-butylcatechol as the substrate. The kinetic data fitted the Michaelis-Menten equation and enabled the obtainment of a rate constant for the catalytic reaction; this rate constant is among the highest obtained for this substrate with the use of dinuclear Cu complexes. DFT calculations discarded a bridging mode binding type of the substrate and suggested a mixed-valence Cu /Cu complex intermediate, in which the spin electron density is mostly concentrated at one of the Cu atoms and at the organic ligand.

Three new coordination compounds, namely, a zero-dimensonal dicopper­(II) complex [Cu2(μ-MeCOO)4­(MeOH)2]­(PTA = O)2 (1), a three-dimensional (3D) copper­(II)-organic framework [Cu3(μ-MeCOO)6­(μ3-PTAO)] n ­·3.5nMeCN (2), and a mixed-valence copper­(I/II) one-dimensional (1D) coordination polymer [Cu3(μ-MeCOO)4­(MeCOO)­(μ-PTA)2­(PTA)] n (3), were self-assembled from copper­(II) acetate and cage-like aminophosphine 1,3,5-triaza-7-phosphaadamantane (PTA) or its P-oxide (PTAO). The obtained products were isolated as air-stable crystalline solids and characterized by IR and electron paramagnetic resonance spectroscopy, thermogravimetric and elemental analysis, as well as single crystal X-ray diffraction. Although all compounds bear dicopper­(II) paddle-wheel tetraacetate [Cu2(μ-MeCOO)4] blocks, they are arranged into very distinct metal–organic architectures. The structure of 2 reveals an intricate 3D metal–organic framework (MOF) driven by the μ3-PTAO spacers acting in an unusual N,N,O-tridentate mode, whereas the compound 3 discloses an infinite 1D wave-like metal–organic chain with the dicopper­(II) [Cu2(μ-MeCOO)4] and monocopper­(I) [Cu­(PTA)­(MeCOO)] blocks being interlinked by the μ-PTA linkers acting in an N,P-bidentate mode. Topological analysis of underlying nets was performed, revealing a decorated uninodal 3-connected framework with the ths topology in 2 and a uninodal 2-connected chain with the 2C1 topology in 3. Compounds 2 and 3 broaden a still very limited family of MOFs or coordination polymers assembled from PTA or its P-oxide building blocks, also showing that PTA can be applied for the generation of unusual mixed-valence copper­(I/II) derivatives. Besides, 2 represents the first example of a copper-containing 3D MOF that is driven by PTAO or any other PTA-derived block. Magnetic properties of 1–3 were investigated, modeled, and discussed in detail, resulting in the exchange coupling parameters (J = −310, −320 cm–1) that indicate a strong antiferromagnetic interaction within the dicopper­(II) paddle-wheel blocks. Moreover, compounds 1 and 2 show a notable catecholase activity in the aerobic oxidation of 3,5-di-tert-butyl-catechol to 3,5-di-tert-butyl-o-benzoquinone; turnover frequency values of up to 81 min–1 were attained.

A series of water-soluble copper(II) complexes based on 2,9-dimethyl-1,10-phenanthroline (dmphen) and mixed-ligands, containing PTA=O (1,3,5-triaza-7-phosphaadamantane-7-oxide) have been synthesized and fully characterized. Two types of complexes have been obtained, monocationic [Cu(NO3)(O-PTA=O)(dmphen)][PF6] (1), [Cu(Cl)(dmphen)2][PF6] (2), and neutral [Cu(NO3)2(dmphen)] (3). The solid-state structures of all complexes have been determined by single-crystal X-ray diffraction. Magnetic studies for the complex 1–3 indicated a very weak antiferromagnetic interaction between copper(II) ions in crystal lattice. Complexes were successfully evaluated for their cytotoxic activities on the normal human dermal fibroblast (NHDF) cell line and the antitumor activity using the human lung carcinoma (A549), epithelioid cervix carcinoma (HeLa), colon (LoVo), and breast adenocarcinoma (MCF-7) cell lines. Complexes 1 and 3 revealed lower toxicity to NHDF than A549 and HeLa cells, meanwhile compound 2 appeared to be more toxic to NHDF cell line in comparison to all cancer lines. Additionally, interactions between the complexes and human apo-transferrin (apo-Tf) using fluorescence and circular dichroism (CD) spectroscopy were also investigated. All compounds interacted with apo-transferrin, causing same changes of the protein conformation. Electrostatic interactions dominate in the 1/2 – apo- Tf systems and hydrophobic and ionic interactions in the case of 3.

This work describes an unexpected generation of a new 3D metal–organic framework (MOF), [Cu 4 (μ-Cl) 6 (μ 4 -O)Cu(OH) 2 (μ-PTA=O) 4 ] n ·2 n Cl-EtOH·2.5 n H 2 O, from copper(II) chloride and 1,3,5-triaza-7-phosphaadamantane 7-oxide (PTA=O). The obtained product is composed of diamandoid tetracopper(II) [Cu 4 (μ-Cl) 6 (μ 4 -O)] cages and monocopper(II) [Cu(OH) 2 ] units that are assembled, via the diamandoid μ-PTA=O linkers, into an intricate 3D net with an nbo topology. Magnetic susceptibility measurements on this MOF in the temperature range of 1.8–300 K reveal a ferromagnetic interaction ( J = +20 cm –1 ) between the neighboring copper(II) ions. Single-point DFT calculations disclose a strong delocalization of the spin density over the tetranuclear unit. The magnitude of exchange coupling, predicted from the broken-symmetry DFT studies, is in good agreement with the experimental data. This copper(II) compound also acts as an active catalyst for the mild oxidation and carboxylation of alkanes. The present study provides a unique example of an MOF that is assembled from two different types of adamantoid Cu 4 and PTA=O cages, thus contributing to widening a diversity of functional metal–organic frameworks.