Synthesis, Crystal Structures, and Magnetic Properties of Two Novel Cyanido-Bridged Heterotrimetallic {CuMnCr} Complexes.

The self-assembly process between the heteroleptic [Cr(phen)(CN)] and [Cr(ampy)(CN)] metalloligands and the heterobimetallic {Cu(valpn)Mn} tecton afforded two heterotrimetallic complexes of formula [{Cu(valpn)Mn(μ-NC)Cr(phen)(CN)}{(μ-NC)Cr(phen)(CN)}]·2CHCN (1) and {[Cu(valpn)Mn(μ-NC)Cr(ampy)(CN)]·2CHCN} (2) [phen = 1,10-phenanthroline, ampy = 2-aminomethylpyridine, and Hvalpn = 1,3-propanedyilbis(2-iminomethylene-6-methoxyphenol)]. The crystal structure of 1 consists of neutral CuMnCr octanuclear units, where two [Cr(phen)(CN)] anions act as bis-monodentate ligands through cyanide groups toward two manganese(II) ions from two [Cu(valpn)Mn] units to form a [{Cu(valpn)Mn}Cr(CN)] square motif. Two [Cr(phen)(CN)] pendant anions in 1 are bound to the copper(II) ions with cis-trans geometry with respect to the bridging [Cr(phen)(CN)] anion. Compound 2 is a sheet-like coordination polymer, where chains constituted by {Cr(ampy)(CN)} spacers act as bis-monodentate ligands toward the manganese(II) ions belonging to the {Cu(valpn)Mn} nodes, which are interlinked by another {Cr(ampy)(CN)} unit that acts as a bridge between the copper(II) and manganese(II) ions of adjacent chains. Magnetic susceptibility measurements in the temperature range of 1.9-300 K were performed for 1 and 2. An overall antiferromagnetic behavior is observed for 1, the ground spin state being described by a spin triplet from the square motif plus two magnetically isolated spin triplets from the two peripheral chromium(III) ions. Ferrimagnetic chains with interacting spins 1/2 (resulting spin of the trimetallic {Cu(valpn)Mn(μ-NC)Cr} fragment) and 3/2 (spin from the bis-monodentate [Cr(ampy)(CN)] with weak interchain ferromagnetic interactions across the cyanide bridge between the chromium(III) and the copper(II) ion from adjacent chains [θ = +3.83(2) cm]) occur in 2, resulting into a ferromagnetic ordering below 3.5 K. The values of the magnetic coupling between the Cu(II) and Mn(II) ions through the double phenoxide bridge [J = -63.1(2) (1) and -62(3) cm (2)] and those between the Cr(III) and the Mn(II) across the single cyanide bridge [J = -7.08(5) and -4.86(6) cm (1) and -8.59(3) cm (2)] agree with the values reported for these exchange pathways in other magnetostructural studies.