The series of complexes [Ru(bpy)(3-n)(btz)(n)][PF(6)](2) (bpy = 2,2'-bipyridyl, btz = 1,1'-dibenzyl-4,4'-bi-1,2,3-triazolyl, 2n = 1, 3n = 2, 4n = 3) have been prepared and characterised, and the photophysical and electronic effects imparted by the btz ligand were investigated. Complexes 2 and 3 exhibit MLCT absorption bands at 425 and 446 nm respectively showing a progressive blue-shift in the absorption on increasing the btz ligand content when compared to [Ru(bpy)(3)][Cl](2) (1). Complex 4 exhibits a heavily blue-shifted absorption spectrum with respect to those of 1-3, indicating that the LUMO of the latter are bpy-centred with little or no btz contribution whereas that of 4 is necessarily btz-centred. DFT calculations on analogous complexes 1'-4' (in which the benzyl substituents are replaced by methyl) show that the HOMO-LUMO gap increases by 0.3 eV from 1'-3' through destabilisation of the LUMO with respect to the HOMO. The HOMO-LUMO gap of 4' increases by 0.98 eV compared to that of 3' due to significant destabilisation of the LUMO. Examination of TDDFT data show that the S(1) states of 1'-3' are (1)MLCT in character whereas that of 4' is (1)MC. The optimisation of the T(1) state of 4' leads to the elongation of two mutually trans Ru-N bonds to yield [Ru(κ(2)-btz)(κ(1)-btz)(2)](2+), confirming the (3)MC character. Thus, replacement of bpy by btz leads to a fundamental change in the ordering of excited states such that the nature of the lowest energy excited state changes from MLCT in nature to MC.

The synthesis, characterization and photophysical investigation of complexes of the form [Ir(R-ppy)2(btz)]PF6 (1 to 3) are reported (btz = 1,1'-dibenzyl-4,4'-bi-1,2,3-triazolyl, R-ppy = 4-(pyrid-2-yl)benzaldehyde (1), 2-phenylpyridine (2) and 2-(2,4-difluorophenyl)pyridine (3)). Complexes 1, 2 and 3 are luminescent and exhibit structured emission bands with vibronic progressions at 532 & 568 nm (ϕ 0.28%), 476 & 508 nm (ϕ 0.82%) and 454 & 483 nm (ϕ 4.3%) respectively. The structuring of these emission bands is indicative of cyclometalated ligand centred emissive states and is further corroborated by the nearly identical emission spectra for 2 and 3 to previously reported analogous complexes with 4-(pyrid-2-yl)-1,2,3-triazole based ancillary ligands. Computational density functional theory calculations on these complexes show that the LUMOs of 2 and 3 are largely btz-centred but with some cyclometalated pyridine π* character. The LUMO of 1 on the other hand is localized primarily on the cyclometalated ligands. Spin population analysis of the lowest lying triplet excited states for these complexes indicate significant spin population over the iridium centres and the aryl and pyridyl moieties in these complexes with virtually no localization of unpaired electrons over the btz ancillary ligands. This is therefore in agreement with the assignment of the emissive state having largely cyclometalated (3)LC character and being independent of the ancillary ligand.

The ligand 4‐azido‐2,2′‐bipyridyl (1) has been used to prepare 1,2,3‐triazole‐substituted ligands through copper‐catalyzed alkyne/azide cycloaddition (CuAAC or “click” chemistry) with phenylacetylene, ethynylferrocene and 2‐ethynylpyridine to yield 4‐(4‐phenyl‐1,2,3‐triazol‐1‐yl)‐2,2′‐bipyridyl (2a), 4‐(4‐ferrocenyl‐1,2,3‐triazol‐1‐yl)‐2,2′‐bipyridyl (2b) and 4‐[4‐(pyridyl‐2‐yl)‐1,2,3‐triazol‐1‐yl]‐2,2′‐bipyridyl (2c). Complexes of the form [Ru(p‐cymene)(Cl)(L)]PF6 (3, L = 1; 4a, L = 2a; 4b, L = 2b) were then prepared and characterized. We also report the synthesis of the complex of the analogous ligand 4,4′‐bisazido‐2,2′‐bipyridyl (1′), [Ru(p‐cymene)(Cl)(1′)]PF6 (3′). Complexes 4a and 4b were also prepared by an alternative route, whereby 3 undergoes CuAAC coupling with phenylacetylene and ethynylferrocene respectively. Complexes prepared with ligands that are pre‐assembled or “clicked” at the metal show identical 1H NMR spectra. CuAAC coupling of 3 and 2‐ethynylpyridine results in the formation of the complex [Ru(p‐cymene)(Cl)(2c)]PF6 (4c), which contains a coordinatively vacant pyridyltriazole moiety. The reaction of [Ru(p‐cymene)(Cl)2]2 with pre‐assembled 2c results in the formation of the dinuclear complex [{Ru(p‐cymene)(Cl)}2(2c)]·2PF6 (5), which incorporates ruthenium atoms at both bipyridyl and pyridyltriazole binding domains. The 1H NMR spectrum of the complex shows two signals for the triazole ring proton as well as duplicate signals for other protons of the bridging ligand, which indicates that 5 is produced as a mixture of diastereoisomers. The complex [{Ru(p‐cymene)Cl}2{di‐4‐([1‐{2,2′‐bipyrid‐4‐yl}triazol‐4‐yl]methyl)ether}][PF6]2 (7) was also prepared through the coupling of 3 with dipropargyl ether.

Metals contribute important roles in biological system. It is recognized that metals are highly linked in cellular and subcellular functions. With the application of novel and experienced tools to study biological and biochemical systems the true role of inorganic salts in biological systems can be studied. Schiff base metal complexes show a broad range of biological activity. The activity of Schiff base ligand is usually increased by complexation with the metal ion. The copper complexes of Schiff bases have striking properties such as antibacterial, antifungal, antiviral, anti-inflammatory, anti-tumor and cytotoxic activities, plant development controller, enzymatic activity and applications in pharmaceutical fields. The divalent cations Zn 2+, Ca 2+ and Mg 2+ prevent cytotoxicity and in vivo antagonize Cd-induced carcinogenesis. Lack of body iron is common in cancer patients and it is associated with complications in surgery and in animal experiments. The transport of iron and other metal ions by the blood plasma is achieved through the formation of protein complexes. Copper is placed as a vital metalloelement and is primarily connected with copper-dependent cellular enzymes. Metals are also used as inorganic drugs for many diseases. In this review our main focused on research undertaken for biological activity study of Cu(II) metal complexes containing Schiff bases over the past few decades.