The structures and properties of the homoleptic copper(I) complexes [Cu(1)(2)][PF(6)] and [Cu(2)(2)][PF(6)] (1 = 6,6'-dimethyl-2,2'-bipyridine, 2 = 6,6'-bis{2-[4-(N,N'-diphenylamino)phenyl]ethenyl}-2,2'-bipyridine) are compared, and a strategy of ligand exchange in solution has been used to prepare eight TiO(2) surface-bound heteroleptic complexes incorporating ligands with bpy metal-binding domains and carboxylate or phosphonate anchoring groups. The presence of the extended π-system in 2 significantly improves dye performance, and the most efficient sensitizers are those with phosphonate or phenyl-4-carboxylate anchoring units; a combination of [Cu(2)(2)](+) with the phosphonate anchoring ligand gives a very promising performance (η = 2.35% compared to 7.29% for standard dye N719 under the same conditions). The high-energy bands in the electronic absorption spectrum of [Cu(2)(2)](+) which arise from ligand-based transitions dominate the spectrum, whereas that of [Cu(1)(2)](+) exhibits both MLCT and ligand π* ← π bands. Both [Cu(1)(2)][PF(6)] and [Cu(2)(2)][PF(6)] are redox active; while the former exhibits both copper-centred and ligand-based processes, [Cu(2)(2)][PF(6)] shows only ligand-based reductions. Results of TD-DFT calculations support these experimental data. They predict an electronic absorption spectrum for [Cu(1)(2)](+) with an MLCT band and high-energy ligand-based transitions, and a spectrum for [Cu(2)(2)](+) comprising transitions involving mainly contributions from orbitals with ligand 2 character. We have assessed the effects of the atomic orbital basis set on the calculated absorption spectrum of [Cu(1)(2)](+) and show that a realistic spectrum is obtained by using a 6-311++G** basis set on all atoms, or 6-311++G** on copper and 6-31G* basis set on all other atoms; a smaller basis set on copper leads to unsatisfactory results. Electronic absorption spectra of six heteroleptic complexes have been predicted using TD-DFT calculations, and the transitions making up the dominant bands analysed in terms of the character of the HOMO-LUMO manifold. The calculational data reveal dominant phosphonate ligand character in the LUMO for the dye found to function most efficiently in practice, and also reveal that the orbital character in the HOMOs of the two most efficient dyes is dominated by the non-anchoring ligand 2, suggesting that ligand 2 enhances the performance of the sensitizer by minimizing back-migration of an electron from the semiconductor to the dye.

A series of 12‐, 14‐, and 16‐membered N2S2‐macrocycles (9–11 and 19–21) with cis and trans‐arrangement of the heteroatoms have been synthesized by high‐dilution cyclization and subsequent reduction of the amides with B2H6. With these ligands the corresponding Cu2+‐complexes were prepared and their UV/VIS spectra, their electrochemistry and their EPR properties have been studied. Generally three absorption bands at 270–320 nm, 330–370 nm and 530–620 nm can be observed in aqueous solution and these have been assigned to the N→Cu2+ and S→Cu2+ charge‐transfer bands and to the d‐d* transition, respectively. The cyclic voltammetry in CH3CN shows in all cases a reversible or quasi‐reversible Cu2+/Cu+‐transition at potentials of 10–480 mV against SHE. The values of g‖ and A‖ obtained from EPR spectra indicate that the geometry of the Cu2+‐complex of the 14‐membered cis‐N2S2‐macrocycle is less distorted than that of the other complexes.

The three ligands 1,4,7,1O-tetraazacyclododecane-1,4,7,1O-tetrakis(methylenephosphonic acid) (l), 1,4,7,1 Itetraazacyclotridecane-1,4,7,1 I-tetrakis(methy1enephosphonic acid) (Z), and 1,4,8,1 l-tetraazacyclotetradecane-1,4,8,1l-tetrakis(methylenephosphonic acid) (3) have been synthesized by condensation of the corresponding macrocycles with formaldehyde and phosphorous acid. The protonation and stability constants with the earthalkali ions have been determined at 25" and I = 0 . 1~ (Me,N(NO,)) by potentiometric titrations. Because of the high values of the first two protonation constants, 'H-NMR measurements were necessary to determine them. Titrations in different supporting electrolytes (NaNO,, KNO,, RbNO,, CsNO,, and Me,N(NO,)) show that their choice is of paramount importance, as the above ligands can form complexes with alkali-metal ions. The potentiometric results for the earth-alkali ions show that beside mononuclear complexes of different degrees of protonation ([MLH,], n = M), also binuclear species are formed ([M,LH,], m = 0-2). It is interesting that 1 with the smallest macrocyclic ring has the greatest tendency to form binuclear complexes, which are so stable that they partially prevent the formation of the corresponding mononuclear species. For [ML]

SummaryThe complexation of Cu(1) and Cu(I1) by a series of 12-, 14-and 16-membered macrocyclic ligands 1 4 containing the N2S2 donor set has been studied potentiometrically, spectrophotometrically and voltammetrically.In the case of Cu(II), mononuclear complexes CuL2' with stability constants of lO'"-l OI5 are formed. In addition, partially hydrolyzed species Cu(L)OH+ are observed at pH > 10 for the 12-membered ligands. For Cu(I), beside the species CuL' with stabilities of 10'2-10'4, the unexpected formation of protonated species CuLH" was detected. In contrast to the well-known general trends in coordination chemistry, the stability of these protonated species increases relative to that of the complexes with the neutral ligand when the ring size and concomitantly the distance between neighbouring donor atoms is decreased. From the stability constants of the Cu(1)-and Cu(I1)-complexes the redox potentials have been calculated and are compared to the values of E , obtained by cyclic voltammetry. Despite the identical donor set the Cu(II)/Cu(I) redox potentials of the complexes are spanning a range of 340 mV or six orders of magnitude in relative stability, reflecting the importance of subtle differences in steric requirements.

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