Crystal structure and magnetic properties of 3,5-pyridinedicarboxylatebridged Re(II)M(II) heterodinuclear complexes (M = Cu, Ni and Co)

The use of the mononuclear rhenium(II) precursor NBu4[Re(NO)Br4(H2pydc)]⋅i-PrOH (1) (H2pydc = 3,5-pyridinedicarboxylic acid) as a metalloligand towards Cu(II), Ni(II) and Co(II) afforded three new heterobimetallic
complexes [Re(NO)Br4(μ-Hpydc)Cu(4,4′ dmbipy)2]⋅(CH3)2CO⋅0.25MeCN (2), [Re(NO)Br4(μ-Hpydc)Ni
(dmphen)2]⋅MeCN (3) and [Re(NO)Br4(μ Hpydc)Co(dmphen)2]⋅2H2O (4), respectively [4,4′ -dmbipy = 4,4′ -dimethyl-2,2′ -bipyridine, dmphen = 2,9-dimethyl-1,10-phenanthroline and Bu4N+ = tetra-n-butylammonium].
The crystal structures of 1 and 2 are reported herein together with the cryomagnetic investigation of 1–4 in the
temperature range of 2.0–300 K. 1 is a mononuclear compound whose structure is made of [Re(NO) Br4(H2pydc)]- complex anions, tetra-n-butylammonium cations and isopropanol molecules of crystallization. Each rhenium(II) ion in 1 is six-coordinate with four bromide ligands in the equatorial positions and a nitrosyl group and one pyridyl-nitrogen atom from an H2pydc ligand filling the axial sites. 2 is a neutral heterobimetallic compound where the [Re(NO)Br4(Hpydc)]2- complex anion acts as a monodentate ligand towards the [Cu(4,4′ -dmbipy)2]2+ complex cation through one carboxylate–oxygen atom. The rhenium(II) ion is six-coordinate in a somewhat distorted octahedral surrounding similar to that in 1. The copper(II) ion in 2 is five-coordinate with four nitrogen atoms from two bidentate 4,4′ -dmbipy ligands and one carboxylate–oxygen atom, describing a surrounding intermediate between square pyramidal and trigonal bipyramidal. Compound 1 behaves as a quasimagnetically
isolated spin doublet with weak antiferromagnetic interactions through space Br⋯Br contacts, ligand field, spin–orbit coupling, tetragonal distortion, and covalence effects considered as variable parameters in a successful simulation of the magnetic data. Compounds 2–4 exhibit also weak intramolecular antiferromagnetic interactions (J) covering the range - 0.60(1) to - 1.50(1) cm- 1 with the Hamiltonian being defined as
H = -JSReSM, M = Cu (2), Ni (3) and Co (4).

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