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

The self-assembly process between the heteroleptic [Cr-III(phen)(CN)(4)](-) and [Cr-III(ampy)(CN)(4)](-) metalloligands and the heterobimetallic {CuII(valpn)MnII}2+ tecton afforded two heterotrimetallic complexes of formula [{Cu-II(valpn)Mn-II(mu-NC)(2)Cr-III(phen)(CN)(2)}(2){(mu-NC)Cr-III(phen)(CN)(3)}(2)]2CH(3)CN (1) and {[Cu-II(valpn)Mn-II(mu-NC)(2)Cr-III(ampy)(CN)(2)](2)2CH(3)CN}(n) (2) [phen = 1,10-phenanthroline, ampy = 2-aminomethylpyridine, and H(2)valpn = 1,3-propanedyilbis(2-iminomethylene-6-methoxyphenol)]. The crystal structure of 1 consists of neutral (Cu2Mn2Cr4III)-Mn-II-Cr-II octanuclear units, where two [Cr(phen)(CN)(4)]- anions act as bis-monodentate ligands through cyanide groups toward two manganese(II) ions from two [Cu-II(valpn)Mn-II](2+) units to form a [{Cu(valpn)Mn}(2)Cr-2(CN)(4)](6+) square motif. Two [Cr(phen)(CN)(4)](-) pendant anions in 1 are bound to the copper(II) ions with cistrans geometry with respect to the bridging [Cr(phen)(CN)(4)](-) anion. Compound 2 is a sheet-like coordination polymer, where chains constituted by {Cr-III(ampy)(CN)(4)} spacers act as bis-monodentate ligands toward the manganese(II) ions belonging to the {Cu-II(valpn)Mn-II} nodes, which are interlinked by another {Cr-III(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 1.9300 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-II(valpn)Mn-II(-NC)Cr-III} fragment) and 3/2 (spin from the bis-monodentate [Cr-III(ampy)(CN)(4)](-) with weak interchain ferromagnetic interactions across the cyanide bridge between the chromium(III) and the copper(II) ion from adjacent chains [theta = +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) cm1 (1) and -8.59(3) cm1 (2)] agree with the values reported for these exchange pathways in other magnetostructural studies.