Synthesis, Crystal Structures, and Magnetic Properties of Two Novel Cyanido-Bridged Heterotrimetallic {Cu<sup>II</sup>Mn<sup>II</sup>Cr<sup>III</sup>} Complexes

The self-assembly process between the heteroleptic [Cr<sup>III</sup>(phen)­(CN)<sub>4</sub>]<sup>−</sup> and [Cr<sup>III</sup>(ampy)­(CN)<sub>4</sub>]<sup>−</sup> metalloligands and the heterobimetallic {Cu<sup>II</sup>(valpn)­Mn<sup>II</sup>}<sup>2+</sup> tecton afforded two heterotrimetallic complexes of formula [{Cu<sup>II</sup>(valpn)­Mn<sup>II</sup>(μ-NC)<sub>2</sub>Cr<sup>III</sup>(phen)­(CN)<sub>2</sub>}<sub>2</sub>{(μ-NC)­Cr<sup>III</sup>(phen)­(CN)<sub>3</sub>}<sub>2</sub>]·2CH<sub>3</sub>CN (<b>1</b>) and {[Cu<sup>II</sup>(valpn)­Mn<sup>II</sup>(μ-NC)<sub>2</sub>Cr<sup>III</sup>(ampy)­(CN)<sub>2</sub>]<sub>2</sub>·2CH<sub>3</sub>CN}<sub><i>n</i></sub> (<b>2</b>) [phen = 1,10-phenanthroline, ampy = 2-aminomethylpyridine, and H<sub>2</sub>valpn = 1,3-propanedyilbis­(2-iminomethylene-6-methoxyphenol)]. The crystal structure of <b>1</b> consists of neutral Cu<sup>II</sup><sub>2</sub>Mn<sup>II</sup><sub>2</sub>Cr<sup>III</sup><sub>4</sub> octanuclear units, where two [Cr­(phen)­(CN)<sub>4</sub>]<sup>−</sup> anions act as bis-monodentate ligands through cyanide groups toward two manganese­(II) ions from two [Cu<sup>II</sup>(valpn)­Mn<sup>II</sup>]<sup>2+</sup> units to form a [{Cu­(valpn)­Mn}<sub>2</sub>Cr<sub>2</sub>(CN)<sub>4</sub>]<sup>6+</sup> square motif. Two [Cr­(phen)­(CN)<sub>4</sub>]<sup>−</sup> pendant anions in <b>1</b> are bound to the copper­(II) ions with <i>cis–trans</i> geometry with respect to the bridging [Cr­(phen)­(CN)<sub>4</sub>]<sup>−</sup> anion. Compound <b>2</b> is a sheet-like coordination polymer, where chains constituted by {Cr<sup>III</sup>(ampy)­(CN)<sub>4</sub>} spacers act as bis-monodentate ligands toward the manganese­(II) ions belonging to the {Cu<sup>II</sup>(valpn)­Mn<sup>II</sup>} nodes, which are interlinked by another {Cr<sup>III</sup>(ampy)­(CN)<sub>4</sub>} 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 <b>1</b> and <b>2</b>. An overall antiferromagnetic behavior is observed for <b>1</b>, 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<sup>II</sup>(valpn)­Mn<sup>II</sup>(μ-NC)­Cr<sup>III</sup>} fragment) and 3/2 (spin from the <i>bis</i>-monodentate [Cr<sup>III</sup>(ampy)­(CN)<sub>4</sub>]<sup>−</sup> 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<sup>–1</sup>]) occur in <b>2</b>, 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 [<i>J</i> = −63.1(2) (<b>1</b>) and −62(3) cm<sup>–1</sup> (<b>2</b>)] and those between the Cr­(III) and the Mn­(II) across the single cyanide bridge [<i>J</i> = −7.08(5) and −4.86(6) cm<sup>–1</sup> (<b>1</b>) and −8.59(3) cm<sup>–1</sup> (<b>2</b>)] agree with the values reported for these exchange pathways in other magnetostructural studies.