Three linear multidentate ligands incorporating terminal 8-thioquinoline rings and flexible polyethylene glycol or semi-rigid o-xylylene spacers were synthesized: pentadentate 1,5-bis(8-quinolylsulfanyl)-3-oxapentane (OESQ), hexadentate 1,8-bis(8-quinolylsulfanyl)-3,6-dioxaoctane (ODSQ) and tetradentate 1,2-bis(quinolin-8-ylsulfanylmethyl)benzene (OBSQ). Reaction of these ligands with various Cu salts afforded three families of Cu(I) and Cu(II) complexes Cu(L1)(L2)Xm: L1 = OESQ and L2/Xm = H2O/(BF4-)2 4, DMF/(BF4-)2 5, H2O/(ClO4-)2 6, NO3-/NO3- 7, NO3-/ClO4- 8, none/ BF4- 9; L1 = ODSQ and L2/Xm = none/(BF4-)2 10, none/(ClO4-)2 11, none/(NO3-)2 12, none/Cu(NO3)42- 13, none/ClO4- 14; L1 = OBSQ and L2/Xm = ClO4-/ClO4- 15, H2O/(BF4-)2 16, DMF/(ClO4-)2 17, DMF/(BF4-)2 18, NO3-/ NO3- 19, H2O/( NO3-)2 20, DMSO/(ClO4-)2 21, NO3-/BF4- 22, none/BF4- 23. For comparison, three Cu complexes Cu(EtSQ)2(ClO4)2 1, Cu(EtSQ)2(ClO4) 2 and Cu(MeSQ)2(ClO4) 3 with the bidentate ligands 8-ethylsulfanylquinoline (EtSQ) and 8-methylsulfanylquinoline (MeSQ) also were prepd. and characterized. The solid-state structures of 1, 3, 7-9, 11, 13, 18·MeCN, 20, 21·MeCN, 22 and 23 were detd. by x-ray diffraction. Compd. 1 shows a distorted octahedral structure with two EtSQ ligands chelating Cu2+ in the equatorial plane and two ClO4- ions interacting in the axial positions. Compds. 7 and 8 exhibit a similarly distorted coordination environment except that one axial O atom comes from the ligand OESQ and the other from the nitrate anion. The hexadentate ligand ODSQ in compds. 11 and 13 wraps around the central Cu2+ ion to form an approx. octahedral geometry resembling that in 1, however, one S atom must move to the axial position and one ether O atom binds in the equatorial plane. In the four compds. 18·MeCN, 20, 21·MeCN and 22, very similar square pyramidal geometries are obsd. around the central Cu2+ ions with four donor atoms from OBSQ occupying three corners of the basal plane and the apical position, the 4th corner being completed by a DMF, H2O, DMSO or NO3- ligand, resp. In the Cu(I) complexes 3, 9 and 23 the metal center is distorted tetrahedrally coordinated with two S and two N donor atoms. The soln. structures were explored by UV-visible and EPR spectroscopy, the Cu(II)/Cu(I) transition and further redn. processes were studied by cyclic voltammetry and UV-visible spectroelectrochem. In contrast to the simple 8-alkylthioquinolines MeSQ and EtSQ the bis(N\%S) ligands allow for a more reversible CuI/CuII transition due to the various effects of steric constraint and addnl. coordination as provided by the spacers. on SciFinder(R)
