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The reaction of Co(AcO) 2 with 6-methyl-2-pyridinecarboxylic acid, and that of CoCl 2 with the isopropyl ester of 2-pyridinecarboxylic acid, both with a 1:2 metal to ligand molar ratio, afford optimum yields for the synthesis of cis -[Co(MeC 5 H 3 NCOO) 2 (H 2 O) 2 ] and cis -[CoCl 2 (C 5 H 4 NCOOPr i ) 2 ], respectively. According to X-ray crystallography they both consist of mononuclear discrete molecules with octahedral coordination around Co(II). The ESR powder spectra of the related Zn phases doped with 0.25% Co(II) show the strong anisotropy of the g and A tensors. The magnetic behaviour of the solid complexes is characteristic of Co(II) systems with important spin–orbit coupling and weak antiferromagnetic interactions. Electronic UV–Vis and magnetic data indicate that these complexes, as well as the already known trans -[Co(C 5 H 4 NCOO) 2 (H 2 O) 2 ], have a high-spin octahedral geometry in solution.

The stoichiometric addition (1:2 metal–ligand) of aqueous alcoholic solutions of the metal salts to similar solutions of 1-methyl-imidazoline-2(3 H )-thione (1-meimz2SH) generated crystalline complexes of general formula, [HgX 2 (1-meimz2SH) 2 ] (X=Cl, Br, I), in good yield. The chemical formulae of the complexes have been characterised by elemental chemical analysis. Infrared and 13 C NMR spectra indicated the presence of the thione form of the heterocyclic ligands in the complexes, as well as their thione–sulfur ligating character. X-ray crystal structure analyses have been performed on the three complexes. The metal in the chloro complex occupies a crystallographic two-fold axis which bisects the SHgS angle. The bromo and iodo complexes occupy general positions, but one of the ligands is disordered in the bromo complex. All of the complexes are mononuclear with the four-coordinate metals possessing distorted tetrahedral geometry. The extent of the distortion is indicated by the angles at the metal which range from 93.71(7) to 127.73(7)°. Metal–sulfur distances range from 2.4514(14) to 2.571(3) A. Metal–halogen distances range from 2.5984(13) A (chloro) through 2.641(3) and 2.647(3) A (bromo) to 2.7866(11) and 2.8047(9) A (iodo). Hydrogen bonds, involving the thioamide hydrogen (NH) and halogen atoms are exclusively intramolecular in the chloro complex, but both intramolecular and intermolecular in the bromo and iodo complexes.

Stoichiometric (1:1) addition of aqueous alcoholic solutions of 1-methylimidazoline-2(3H)-thione (meimz2SH) to a similar series of mercury(II) halides produced crystalline complexes of empirical formula [HgX2(meimz2SH)] (X = Cl, Br, l). The chemical formulae of the complexes have been characterised by elemental chemical analysis. IR and 11C NMR spectra indicated the presence of the thione form of the heterocyclic ligands in the complexes, as well as their thione-sulphur ligating character. The crystal structure of [HgBr2(meinz2SH)]2] has been determined by single crystal X-ray diffraction methods. The complex crystallises in a monoclinic unit cell with a = 7.7063(13), b = 14.471(3), c = 25.705(4) A , β = 95.114(9)°, Z = 6 (dimers) and space group P21/n. The asymmetric unit consists of one general dimeric complex and half of a dimeric molecule on an inversion centre. Weak intermolecular secondary contacts occur between terminal bromine and mercury(II) atoms (Hg⋙Br=3.587−3.791 A). These contacts link the bromo-bridged dimers into weakly associated polymeric sheets, Consequently, the mercury(II) atoms have distorted trigonal-bipyramidal coordination in this complex. The apical sites of the trigonal-bipyramidal polyhedra are occupied by terminal bromine (HgBrterminal = 2.489(2)−2.532(2) A) and terminal thione-sulphur (HgS = 2.405(4) − 2.419(4) A) atoms. Equatorial bromine atoms consist of the long intermolecular bromine contacts and the bridging bromine atoms (HgBrbridging = 2.659(2) − 2.859(3) A). The latter arre also involved in the central, binuclear asymmetric Hg2(μ-Br)2 cores. These cores also contain long Hg⋙Hg′ contacts (3.901 and 4.041 A) and narrow bridgingangles (HgBrHg = 89.90(5)−90.62(5)°). Further intermolecular contacts between the ligand amide (NH) groups and some of the bridging and terminal bromine atoms (NH…Br = 2.555−2.683 A) generate an extensive H-bonded network.

The complex [Cu4(tzdt)4(tzdtH)2] has been electrochemically synthesized in toluene using a copper anode, a platinum cathode and the parent ligand, 1,2-thiazolidine-2-thione (tzdtH). The supporting electrolyte was tetrabutyl ammonium tetrafluoroborate. The major product was the toluene solvated polymer [Cu4(tzdt)4·(toluene)n] with the title complex obtained as a minor product. The presence of both thionate and thione forms of 1,3-thiazolidine-2-thione was indicated in the title complex by means of IR and proton NMR spectra. The colourless, diamagnetic complex crystallises in an orthorhombic cell with a=21.2452(4), b=24.9586(4), c=11.8536(3) A , V=6285.4(2) A 3 , Z=8 (tetramers), space group Fdd2, final R1=0.0446 from 1564 reflections with F02>2σ(F02). The tetranuclear complex has crystallographically imposed C2 symmetry with crystallographic axis bisecting the central Cu4 core of the complex. The central cyclic Cu4 core of the complex has an ‘open-butterfly’, configuration with CuCu distances and angles in the range 2.8887(15)–3.8357(16) A and 47.51(3)–78.27(4)°, respectively. The four deprotonated ligands are trinuclear face-bridging, μ3-S,N(η2-S,η1-N), towards the four triangular Cu3 faces of the central Cu4 core. The ‘spinal’ copper(I) atoms have distorted trigonal S2N coordination from three different ligands. The ‘wing-tip’ copper(I) atoms are additionally coordinated by monodentate η1-S donating 1,3-thiazolidine-2-thione ligands and consequently have distorted tetrahedral S,N coordination from four different ligands. Bridging CuN distances are in the range 2.225(2)–2.362(2) A, the monodentate terminal CuS distance is 2.4908(18) and the CuN distances a1.996(7) and 2.0017(5) A. Neighbouring tetranuclear complexes are held together in the solid state by a combination of long-range Cu…S and Sendo…Sendo contacta. Hydrogen bonds, involving bridging thio sulfur atoms and the thioamide nitrogen atoms of terminal ligands ( NH…S =3.487 A ), are also involved. The title complex is air-stab and decomposes, endothermically, to copper(II) oxide in flowing air (226–836°C).

The series of complexes [HgX 2 (C 5 H 4 NCOOR)] (XCl, Br or I; RMe, Et, Pr n , Pr i ) has been obtained by the addition reaction of esters of 2-pyridinecarboxylic acid to mercury(II) halides irrespective of the ester to metal molar ratio used. The X-ray crystal structures of the four chloro complexes [HgCl 2 (C 5 H 4 NCOOR)], R&.zdbnd;Mc ( 1 ), Et ( 4 ) and Pr n ( 7 ) and Pr i ( 10 ), have been determined. There is a remarkable structural variety within such a closely related family, probably due to different sizes of the substituents. Complexes 1 and 4 adopt polymeric structures. However, the one-dimensional chain in 1 consists of consecutive symmetrically bridged Hg(μ-Cl) 2 Hg dimeric units linked by secondary Hg…Cl interactions while in 4 it is formed by monomeric HgCl 2 L units, LC 5 H 4 NCOOEt, bound by a unique non-plana bis(chloride) asymmetric Hg 2 Cl 2 bridge. In both structures, mercury achieves an effectove six-coordination. The structures of 7 and 10 comprise only discrete centrosymmetric dimers and tetramers, respectively. The latter can be described as a central ClLHg(μ-Cl) 2 HgLCl unit, LC 3 H 4 NCOOPr n , bound to two additional HgCl 2 L molecules by means of long-range Hg·.Cl interactions. Mercury shows an effective five-coordination in 7 and five-and six-coordination in 10 . The four structures, based on a backbone containing mercury and chlorine atoms exclusively, have been correlated. The geometric parameters of their basic Hg(μ-Cl) 2 Hg structural motifs are also found in other HgCl 2 (L) adducts and seem to be independent of the coordination number and geometry about mercury as well as of the unidentate or bidentate nature of the L ligand.