Zinc(II) and cadmium(II) complexes with the decahydro-closo-decaborate anion and phenyl-containing benzimidazole derivatives with linker N N or C N group

N^N^C-Cyclometalated rhodium(III) complexes with isomeric pyrimidine-based ligands: unveiling the impact of isomerism on structural motifs, luminescence and cytotoxicity

The impact of isomerism of pyrimidine-based ligands and their rhodium(III) complexes with regard to their structures and properties was investigated. Two isomeric ligands, 4-(3,5-dimethyl-1H-pyrazol-1-yl)-2,5-diphenylpyrimidine (HL2,5) and 4-(3,5-dimethyl-1H-pyrazol-1-yl)-2,6-diphenylpyrimidine (HL2,6), were synthesized. The ligands differ by the degree of steric bulk: the molecular structure of HL2,5 is more distorted due to presence of pyrazolyl and phenyl groups in the neighbouring positions 4 and 5 of the pyrimidine ring. The complexation of HL2,5 and HL2,6 with RhCl3 leads to the sp2 C-H bond activation, resulting in the isolation of two complexes, [RhL2,5(Solv)Cl2]·nEtOH and [RhL2,6(Solv)Cl2]·nEtOH (Solv = H2O, EtOH), with the deprotonated forms of the pyrazolylpyrimidine molecules which coordinate the Rh3+ ion as N^N^C-tridentate ligands. According to DFT modelling, the mechanism of the deprotonation involves (i) the C-H bond breaking in the 2-phenyl group followed by the coordination of the C atom to the Rh atom, (ii) the protonation of coordinated chlorido ligand, (iii) the ejection of the HCl molecule and (iv) the coordination of the H2O molecule. The ligand isomerism has an impact on emission properties and cytotoxicity of the complexes. Although the excited states of the complexes effectively deactivate through S0/T1 and S0/S1 crossings associated with the cleavage of the weak H2O ligands upon excitation, the [RhL2,5(Solv)Cl2]·nEtOH complex appeared to be emissive in the solid state, while [RhL2,6(Solv)Cl2]·nEtOH is non-emissive at all. The complexes show significant cytotoxic activity against cancerous HepG2 and Hep2 cell lines, with the [RhL2,6(Solv)Cl2]·nEtOH complex being more active than its isomer [RhL2,5(Solv)Cl2]·nEtOH. On the other hand, noticeable cytotoxicity of the latter against HepG2 is supplemented by its non-toxicity against non-cancerous MRC-5 cells.

Spontaneous Isomerization [trans-B20H18]2– → [iso-B20H18]2– during Cobalt(II) Complexation with Phenanthroline

Abstract

In this work, the cobalt(II) complexation with 1,10-phenanthroline (Phen) in the presence of the [trans-B20H18]2– anion has been studied. At a Co : Phen = 1 : 2 ratio in acetonitrile, a binuclear cobalt(II) complex with bridging chlorine atoms and the boron cluster anion as a counterion [(Phen)2Co(µ-Cl)2Co(Phen)2][trans-B20H18] has been isolated. However, during slow crystallization (within a month), spontaneous isomerization of [trans-B20H18]2– into [iso-B20H18]2– is observed. It has been established by X-ray diffraction analysis that in the crystal of the final compound [(Phen)2Co(µ-Cl)2Co(Phen)2][trans-B20H18]1/3[iso-B20H18]2/3, co-crystallization of both isomeric forms of the octadecahydroeicosaborate anion is observed for the first time. The presence of the iso form of the boron cluster anion is also confirmed by IR spectroscopy data: the spectrum of the product shows a band of stretching vibrations of the BHB bridge groups at 1773 cm–1, which is absent in the trans-form of the boron cluster.

Gold(III) Complexation in the Presence of the Macropolyhedral Hydridoborate Cluster [B20H18]2−

Gold(III) complexation with the octadecahydrido-eicosaborate anion [B20H18]2− was studied for the first time. It was found that when gold(III) complexes [Au(L)Cl2]BF4 (L = bipy, phen) reacted with [B20H18]2−, complexes [Au(L)Cl2]2[B20H18] were isolated. The compounds consisted of a cationic gold(III) complex [Au(L)Cl2]+ and the hydridoborate cluster as a counterion. X-ray diffraction studies revealed weak B–H...Au interactions for both compounds. Note that more reactive anions [BnHn]2− (n = 10, 12) in similar reactions with gold(III) complexes resulted in gold mirror reactions.