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

The self-assembly process between the heteroleptic [CrIII(phen)­(CN)4] and [CrIII(ampy)­(CN)4] metalloligands and the heterobimetallic {CuII(valpn)­MnII}2+ tecton afforded two heterotrimetallic complexes of formula [{CuII(valpn)­MnII(μ-NC)2CrIII(phen)­(CN)2}2{(μ-NC)­CrIII(phen)­(CN)3}2]·2CH3CN (1) and {[CuII(valpn)­MnII(μ-NC)2CrIII(ampy)­(CN)2]2·2CH3CN}n (2) [phen = 1,10-phenanthroline, ampy = 2-aminomethylpyridine, and H2valpn = 1,3-propanedyilbis­(2-iminomethylene-6-methoxyphenol)]. The crystal structure of 1 consists of neutral CuII2MnII2CrIII4 octanuclear units, where two [Cr­(phen)­(CN)4] anions act as bis-monodentate ligands through cyanide groups toward two manganese­(II) ions from two [CuII(valpn)­MnII]2+ units to form a [{Cu­(valpn)­Mn}2Cr2(CN)4]6+ square motif. Two [Cr­(phen)­(CN)4] pendant anions in 1 are bound to the copper­(II) ions with cis–trans geometry with respect to the bridging [Cr­(phen)­(CN)4] anion. Compound 2 is a sheet-like coordination polymer, where chains constituted by {CrIII(ampy)­(CN)4} spacers act as bis-monodentate ligands toward the manganese­(II) ions belonging to the {CuII(valpn)­MnII} nodes, which are interlinked by another {CrIII(ampy)­(CN)4} 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 {CuII(valpn)­MnII(μ-NC)­CrIII} fragment) and 3/2 (spin from the bis-monodentate [CrIII(ampy)­(CN)4] 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–1]) 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–1 (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 (1) and −8.59(3) cm–1 (2)] agree with the values reported for these exchange pathways in other magnetostructural studies.