Synthesis and mononuclear complexes of the bis-bidentate ligand 2,5-di(2-pyridyl)-1,3,4-thiadiazole (dptd): spin crossover in [Fe(II)(dptd)2(NCSe)2] and [Fe(II)(dptd)2(NCBH3)2]·H2O.

A simple and convenient protocol for the synthesis of the ligand 2,5-di(2-pyridyl)-1,3,4-thiadiazole (dptd) has been developed. Five new 2 : 1-type iron(II), cobalt(II), nickel(II) and copper(II) complexes have been prepared and structurally characterised, all of which feature the mononuclear trans-(N',N(1))(2) coordination mode. Spin crossover behaviour has been found for [Fe(II)(dptd)(2)(NCSe)(2)] (2) and [Fe(II)(dptd)(2)(NCBH(3))(2)]·H(2)O (3·H(2)O) with T(1/2) = 192 and 285 K, respectively, reflecting the increasing ligand field strength of the respective co-ligands and showing that the [Fe(II)(dptd)(2)L(2)] unit is suitable for the investigation of the co-ligand field effects on T(1/2).

Dependence of the chemical properties of macrocyclic [Ni(II)(2)L(μ-O(2)CR)](+) complexes on the basicity of the carboxylato coligands (L(2-) = macrocyclic N(6)S(2) ligand).

The dependence of the properties of mixed ligand [Ni(II)(2)L(μ-O(2)CR)](+) complexes (where L(2-) represents a 24-membered macrocyclic hexaamine-dithiophenolato ligand) on the basicity of the carboxylato coligands has been examined. For this purpose 19 different [Ni(II)(2)L(μ-O(2)CR)](+) complexes (2-20) incorporating carboxylates with pK(b) values in the range 9 to 14 have been prepared by the reaction of [Ni(II)(2)L(μ-Cl)](+) (1) and the respective sodium or triethylammonium carboxylates. The resulting carboxylato complexes, isolated as ClO(4)(-) or BPh(4)(-) salts, have been fully characterized by elemental analyses, IR, UV/vis spectroscopy, and X-ray crystallography.

Two-step spin crossover in the mononuclear iron(II) complex [Fe(II)(L)(2)(NCS)(2)] (L = 2,5-di-(2-pyridyl)-1,3,4-thiadiazole).

The first iron(ii) complex of 2,5-di-(2-pyridyl)-1,3,4-thiadiazole (L), namely [Fe(II)(L)(2)(NCS)(2)], has been synthesised and studied by magnetic susceptibility measurements, Mössbauer spectroscopy and X-ray diffraction. It has been found to undergo thermally-induced spin crossover featuring two well-separated, abrupt steps at T(1/2)(1) = 167 K and T(1/2)(2) = 112 K.

Triazolopyridines as ligands: structural diversity in iron(II), cobalt(II), nickel(II) and copper(II) complexes of 3-(2-pyridyl)-[1,2,4]triazolo[4,3-a]- pyridine (L¹⁰) and spin crossover in [Fe(II)(L¹⁰)₂(NCS)₂].

The coordination chemistry of the ligand 3-(2-pyridyl)-[1,2,4]triazolo[4,3-a]pyridine (L¹⁰) has been investigated and iron(II), cobalt(II), nickel(II) and copper(II) complexes featuring diverse structural motifs have been prepared. In the 2 : 1-type complexes [Co(II)(L¹⁰)₂(MeOH)₂](ClO₄)₂ (20), [Ni(II)(L¹⁰)₂(MeOH)₂](ClO₄)₂ (21), [Cu(II)(L¹⁰)₂(MeOH)₂](ClO₄)₂ (22), [Co(II)(L¹⁰)₂(H₂O)₂](ClO₄)₂ (23) and [Cu(II)(L¹⁰)₂(ClO₄)₂] (24) the metal centres are N₄O₂ octahedrally coordinated with two N²,N(pyr) bidentate ligands L¹⁰ in the equatorial positions. In the N₆ octahedral 4 : 1-type complex [Co(II)(L¹⁰)₄](ClO₄)₂·H₂O (25) both axially coordinating N¹ unidentate and equatorially bound N²,N(pyr) bidentate ligands L¹⁰ are observed.

Tricopper(II) complexes of unsymmetrical macrocycles incorporating phenol and pyridine moieties: the development of two stepwise routes.

Two stepwise approaches to preparing large unsymmetrical macrocycles incorporating diethylenetriamine lateral units are described: the first utilises protecting group chemistry, whereas the second exploits irreversible amide bond formation in the presence of an excess of the amine. In the first approach condensation of two equivalents of N-acetyldiethylenetriamine 1 with 2,6-diformyl-4-methylphenol, followed by a sodium borohydride reduction of the newly formed imine bonds and acidic removal of the protecting groups, yields a phenol-containing "two-armed" precursor as an HCl salt 2. Using the second approach the new pyridine-containing "two-armed" precursor , is prepared from 2,6-dimethylpyridinedicarboxylate and an excess of diethylenetriamine.

Synthesis and some first-row transition-metal complexes of the 1,2,4-triazole-based Bis(terdentate) ligands TsPMAT and PMAT.

The employment of a strategy based on nucleophilic substitution, rather than Schiff base condensation, for the preparation of 1,2,4-triazole-based ligands has been investigated and has led to the synthesis of two new ligands, 4-amino-3,5-bis{[N-(2-pyridylmethyl)-N-(4-toluenesulfonyl)amino]methyl}-4H-1,2,4-triazole (TsPMAT, 14) and 4-amino-3,5-bis{[(2-pyridylmethyl)amino]methyl}-4H-1,2,4-triazole (PMAT, 15). These are the first examples of bis(terdentate) ligands incorporating the 1,2,4-triazole unit. TsPMAT (14) forms a dinuclear 2:2 complex with Co(BF4)2.

The first X-ray crystal structure determination of a dinuclear complex trapped in the [low spin-high spin] state: [Fe(II)2(PMAT)2](BF4)4.DMF.

The two metal centres in the doubly 1,2,4-triazole-bridged spin crossover complex [Fe(II)2(PMAT)2](BF4)4.DMF (1.DMF) are trapped in different spin states below ca.

Realization of unusual ligand binding motifs in metalated container molecules: synthesis, structures, and magnetic properties of the complexes [(LMe)Ni2(mu-L')]n+ with L'=NO3-, NO2-, N3-, N2H4, pyridazine, phthalazine, pyrazolate, and benzoate.

A series of dinickel(II) complexes with the 24-membered macrocyclic hexaazadithiophenol ligand H(2)L(Me) was prepared and examined. The doubly deprotonated form (L(Me))(2-) forms complexes of the type [(L(Me))Ni2II(mu-L')](n+) with a bioctahedral N(3)Ni(II)(mu-SR)(2)(mu-L')Ni(II)N(3) core and an overall calixarene-like structure. The bridging coordination site L' is accessible for a wide range of exogenous coligands.