Reactions of (NBu4)[ReOCl4] and 3,3,3',3'-tetraalkyl-1,1'-isophthaloylbis(thioureas), H2phth(R2tu)2 where R = Et, i-Bu, in hot MeOH with the addition of Et3N give red products of the composition [ReO(OMe){phth(R2tu)2}]2 (8a, R = Et; 8b, R = i-Bu). X-ray structures of 8 reveal symmetric binuclear complexes containing two almost coplanar organic ligands, each of which coordinates to two rhenium centers via the two bidentate-O,S moieties. The octahedral coordination spheres of the rhenium atoms are completed by each one oxo and one methoxido ligand which are directed perpendicular to the plane defined by the {phth(R2tu)2}(2-) ligands. While in 8a, both methoxido ligands point to the same side of the described plane and form a syn isomer, the MeO(-) ligands in 8b are located at opposite sides and form an anti isomer. Studies in solution show that there exists a reversible equilibrium between the anti and syn isomers. Dimerization/condensation of complexes 8 with the formation of tetranuclear complexes of the composition [{ReO{phth(R2tu)2}}2O]2 (9) and/or polynuclear species is observed in solutions, which do not contain MeOH.

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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. The possibility of accessing the [Ni(II)(2)L(μ-O(2)CR)](+) complexes by carboxylate exchange reactions has also been examined. The main findings are as follows: (i) Substitution reactions between 1 and NaO(2)CR are not affected by the basicity or the steric hindrance of the carboxylate. (ii) Complexes 2-20 form an isostructural series of bisoctahedral [Ni(II)(2)L(μ-O(2)CR)](+) compounds with a N(3)Ni(μ-SR)(2)(μ-O(2)CR)NiN(3) core. (iii) They are readily identified by their ν(as)(CO) and ν(s)(CO) stretching vibration bands in the ranges 1684-1576 cm(-1) and 1428-1348 cm(-1), respectively. (iv) The spin-allowed (3)A(2g) → (3)T(2g) (ν(1)) transition of the NiOS(2)N(3) chromophore is steadily red-shifted by about 7.5 nm per pK(b) unit with increasing pK(b) of the carboxylate ion. (v) The less basic the carboxylate ion, the more stable the complex. The stability difference across the series, estimated from the difference of the individual ligand field stabilization energies (LFSE), amounts to about 4.2 kJ/mol [Δ(LFSE)(2,18)]. (vi) The "second-sphere stabilization" of the nickel complexes is not reflected in the electronic absorption spectra, as these forces are aligned perpendicularly to the Ni-O bonds. (vii) Coordination of a basic carboxylate donor to the [Ni(II)(2)L](2+) fragment weakens its Ni-N and Ni-S bonds. This bond weakening is reflected in small but significant bond length changes. (viii) The [Ni(II)(2)L(μ-O(2)CR)](+) complexes are relatively inert to carboxylate exchange reactions, except for the formato complex [Ni(II)(2)L(μ-O(2)CH)](+) (8), which reacts with both more and less basic carboxylato ligands.

The synthesis of binuclear Cu II -, Ni II -, Zn II -, Cd II -and Pd II -complexes of the quadridentate ligand N,N,Nٞ,Nٞ-tetraisobutyl-NЈ,NЉ-isophthaloylbis(thiourea) and the crystal structures of the Cu II -and Ni II -complexes are reported. The Cu II -complex crystallizes in two polymorphic modifications: triclinic, P1 (Z ϭ 1) and monoclinic, P2 1 /c (Z ϭ 2). The Ni II -complex was found to be isostructural with the triclinic modification of the copper complex. The also prepared Pd II -, Zn II -and Cd II -complexes could not be characterized by X-ray analysis. However, EPR studies of diamagnetically diluted Cu II /Pd II -and Cu II /Zn II -powders show axiallysymmetric g and A Cu tensors suggesting a nearly planar co-ordination within the binuclear host complexes. Diamagnetically diluted Cu II /Cd II powder samples could not be prepared. In the EPR spec-867 tra of the pure binuclear Cu II -complex exchange-coupled Cu II -Cu II pairs were observed. According to the large Cu II -Cu II distance of about 7,50 Å a small fine structure parameter D ϭ 26 · 10 Ϫ4 cm Ϫ1 is observed; T-dependent EPR measurements down to 5 K reveal small antiferromagnetic interactions for the Cu II -Cu II dimer. Besides of the dimer in the EPR spectra the signals of a mononuclear Cu II species are observed whose concentration is T-dependent. This observation can be explained assuming an equilibrium between the binuclear Cu II -complex (Cu II -Cu II pairs) and oligomeric complexes with "isolated" Cu II ions. A. Rodenstein, J. Griebel, R. Richter, R. Kirmse Darauf aufbauend berichteten Koch et al. in den letzten Jahren die Synthese von binuklearen Ni II -, Pd II -und Pt II -Komplexen des Typs 4, wobei jeweils ein Ni II -Komplex ( R ϭ Et) [16], ein Pd II -Komplex (R ϭ n-Bu) [17] und ein Pt II -Komplex (R ϭ Et) [14] strukturell charakterisiert wurden. In weiteren Arbeiten wurde die Wechselwirkung der Komplexe der Ni-Triade mit Halogenen und Stickstoff-Heterocyclen unter dem Aspekt der Bildung von Netzwerkstrukturen untersucht [17Ϫ19].Kürzlich berichteten wir die Synthese und die Struktur des bis-bidentaten Liganden N,N,Nٞ,Nٞ-Tetraisobutyl-NЈ,NЉ-isophthaloylbis(thioharnstoff) (2b) und dessen binuklearen Co II -Komplexes, des ersten eines N-Acylthioharnstoffliganden überhaupt [20]. Im Mittelpunkt dieser Arbeit stehen die Synthese weiterer binuklearer Komplexe von 2b mit M ϭ Cu II (5a), Ni II (5b), Zn II (5c), Cd II (5d) und Pd II (5e) sowie EPR-Untersuchungen am binuklearen Cu II -Komplex 5a, wo aufgrund unserer früheren Arbeiten am Cu II -Dreikernkomplex [12] schwache, aber nachweisbare "long-range" Cu II -Cu II -Wechselwirkungen erwartet wurden. Die von uns bei früheren EPR-Untersuchungen an mononuklearen Cu II -Komplexen mit N-Acylthioharnstoffliganden beobachteten geringen Linienbreiten der EPR-Signale [3,8,21,22] und die damit verbundene höhere Auflösung sollten hierbei hilfreich sein. Neben den Strukturen des Cu II -(5a) und des Ni II -Komplexes 5b berichten wir über die EPR-Untersuchungen am binuklearen Cu II -Komplex 5a selbst sowie an dia...

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