[μ-N,N,N′,N′-Tetrakis(2-pyridylmethyl)pentane-1,5-diamine]bis[dichloridocopper(II)] sesquihydrate

In the title dinuclear copper complex, [Cu2Cl4(C29H34N6)]·1.5H2O, both CuII ions are coordinated in a slightly distorted square-pyramidal environment in which the N atoms of the dipicolylamine group and a chloride ligand form the basal plane. The apical position is occupied by a second chloride atom. The Cu—N distances involving the pyridine N atoms differ slightly from each other and the Cu—N distance involving the tertiary N atom is the longest. The apical Cu—Cl distance is elongated compared to its basal counterpart due to typical Jahn–Teller distortion. In the crystal structure, complex and water molecules are linked via intermolecular O—H⋯O and O—H⋯Cl hydrogen bonds into chains along [001]. One of the water molecules was refined with half occupancy.

In the title dinuclear copper complex, [Cu 2 Cl 4 (C 29 H 34 N 6 )]Á-1.5H 2 O, both Cu II ions are coordinated in a slightly distorted square-pyramidal environment in which the N atoms of the dipicolylamine group and a chloride ligand form the basal plane. The apical position is occupied by a second chloride atom. The Cu-N distances involving the pyridine N atoms differ slightly from each other and the Cu-N distance involving the tertiary N atom is the longest. The apical Cu-Cl distance is elongated compared to its basal counterpart due to typical Jahn-Teller distortion. In the crystal structure, complex and water molecules are linked via intermolecular O-HÁ Á ÁO and O-HÁ Á ÁCl hydrogen bonds into chains along [001]. One of the water molecules was refined with half occupancy.

Comment
The described ligand has been used as starting material for hydrothermal synthesis of metal-organic transition metal/molybdateoxide frameworks in the principal author's laboratory (Bartholomä, unpublished results). The dipicolylamine moiety has originally been developed in our laboratory as metal chelating entity for binding of the M(CO) 3 core (M = Re, 99m Tc) for radiopharmaceutical purposes. However, a different coordination mode has been observed for the M(CO) 3 core in which the dipicolylamine metal chelate is coordinated in a facial manner (Bartholomä, 2009).
The title complex was prepared as part of a series with different cadmium and copper salts to study the coordination properties of the ligand with these metals without the interaction of metaloxide clusters (Bartholomä, 2010a,b,d). The shorter homologue N 1 ,N 1 ,N 4 ,N 4 -tetrakis(pyridin-2-ylmethyl)butane-1,4-diamine gave structurally similar complexes with copper bromide as metal salt. The corresponding Cu-N py distances are 2.015 (6) Å and 2.019 (6) Å and the Cu-N tert distance was determined to 2.053 (5) Å (Bartholomä, 2010c).

Experimental
N 1 ,N 1 ,N 5 ,N 5 -tetrakis(pyridin-2-ylmethyl)pentane-1,5-diamine. An amount of 1.00 g (9.78 mmol) 1,5-diaminopentane was dissolved in 30 ml anhydrous dichloroethane under an inert atmosphere (argon) followed by the addition of 3.91 ml (41.10 mmol) pyridine-2-carboxaldehyde. The mixture was stirred for 15 min at r.t. and then cooled with an ice bath prior to the portionwise addition of 12.44 g (58.72 mmol) sodium triacetoxyborohydride (gas evolution, exothermic reaction). The reaction was stirred overnight allowing the temperature slowly to rise to room temperature. The reaction was quenched by the dropwise addition of saturated sodium bicarbonate solution and stirring was continued until the gas evolution ceased.
The mixture was separated and the organic layer was further washed with saturated sodium bicarbonate solution, water and brine. The organic phase was dried with anhydrous sodium sulfate, filtered and the solvent removed under reduced pressure.
The crude reaction mixture was then purified by silica gel column chromatography starting with chloroform and increasing gradient to chloroform:methanol 10:1 (v/v). Yield

sup-2
Synthesis of metal complex. To 2 ml of an aqueous solution of copper chloride, two equivalents (50 mg, 0.11 mmol) of N 1 ,N 1 ,N 5 ,N 5 -tetrakis(pyridin-2-ylmethyl)pentane-1,5-diamine in 2 ml methanol were added followed by the addition of 2 ml N,N-dimethylformamide. Single crystals were obtained after a week by slow evaporation of the solvents at room temperature.

Refinement
All the H atoms were placed in idealized positions and refined by the riding model approximation with C-H aryl = 0.95 Å, C-H methyl = 0.98Å and C-H methylene = 0.99Åand U iso (H) = 1.5U eq (C methyl ) and 1.2U eq (C methylene/aryl ). Water hydrogen atoms were initially located in the difference Fourier map but were then refined with O-H = 0.84 (2) Å and U iso (H) = 1.5 U eq (O). Fig. 1. The molecular structure of the title complex. The displacement ellipsoids are drawn at 50% probability level. solvent water molecules and hydrogen atoms are omitted for clarity.  (7) C29-H29 0.9500