Synthesis and Spectroscopic and Magnetic Characterization of Tris(3,5-dimethylpyrazol-1-yl)borate Iron Tricyanide Building Blocks, a Cluster, and a One-Dimensional Chain of Squares

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Abstract

The synthesis and spectroscopic and magnetic characterization of several hydridotris(3,5-dimethylpyrazol-1yl)borate (Tp*) iron(II) and iron(III) tricyanide complexes, a rectangular cluster, and a one-dimensional chain of squares are described. Treatment of [NEt4][(Tp*)Fe(III)(CN)3] (3) with manganese(II) triflate in dimethylformamide (DMF) affords rectangular clusters (6, {[(Tp)Fe(CN)2(mu-CN)Mn(DMF)4]2[OTf]2}.2DMF), while tosylate salts afford one-dimensional networks (5, {Mn(II)(DMF)2(mu-OTs)(mu-NC)2(NC)Fe(III)(Tp*)}n) containing embedded [(Tp*)2Fe(III)2Mn(II)2(CN)6]2+ clusters via in situ trapping; the cluster and network crystallize in the monoclinic (6, P2(1)/n) and triclinic (5, P1) space groups, respectively. The 1-D network (5) appears to be derived from {cis-(mu-O3SC6H4Me)2Mn(II)(DMF)4}n (4, P2(1)/n), which is obtained via crystallization of Mn(OTs)2 from DMF/Et2O mixtures. For 4, magnetic studies indicate that the Mn(II) centers are magnetically isolated, with calculated J, g, and theta constants of 6.7 x 10(-3) cm(-1), 2.03, and -0.52 K. Additional magnetic studies of 5 and 6 indicate that the [(Tp*)Fe(III)(CN)3]- centers are highly anisotropic (g = 2.9) and are antiferromagnetically coupled to adjacent Mn(II) centers. For 5 and 6, fitting of the chiT vs T data via the Curie-Weiss expression affords Curie (6.25 and 10.8 cm(3) K mol(-1)) and Weiss (-14.37 and -8.80 K) constants that are consistent with antiferromagnetically coupled low-spin Fe(III) and high-spin Mn(II) centers; least-squares fitting of the chiT vs T data using molecular field theory affords g(avg.), J1, J2, and J' values of 2.25, -1.72, -0.58, and -0.12 cm(-1) for 5. Overall, bridging tosylates appear to be poor communicators of spin information. For 6, the g, J1, and J2 (2.15, -2.02, and -0.78 cm(-1)) values were obtained via least-squares fitting of the chiT vs T data using an expression derived using the Kambe vector coupling method; simulations of the data via MAGPACK afford g(avg.) and J(iso) values of 2.1 and -2.1 cm(-1).

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