Synthesis and characterization of one- and two-dimensional octacyanometalate(V) networks: {[ trans-M II(DMF) 4][ cis-M II(DMF) 4] 2[M V(CN) 8] 2} n (M II = Mn, Fe, Ni; M V = Mo, W)

Abstract

Treatment of several binary transition metal p-toluenesulfonates [M II(OTs) 2] with tri(butyl)ammonium octacyanomolybdate(V) or -tungstate(V) in DMF readily affords a series of one- and two-dimensional crystalline octacyanometalate networks of [M II(DMF) 4] 3[M V(CN) 8] 2 (M V = Mo, W; M II = Mn, 5, 6; Ni, 7, 8) stoichiometry. Treatment of Fe(OTs) 2 with [HBu 3N] 3[W V(CN) 8] in DMF affords amorphous precipitates while FeCl 3 affords crystalline [Fe II(DMF) 6] 2[W IV(CN) 8] ( 9) salts; two-dimensional [Fe II(DMF) 4] 3[W V(CN) 8] 2 ( 10) lattices are obtained from 9 after standing several months. The structures of 5 and 8 contain [ cis-M II(DMF) 4(μ-NC) 2] 2+ and [ trans-M II(DMF) 4(μ-NC) 2] 2+ units that are linked via cyanides to three-connected [M V(CN) 5(μ-CN) 3] 3− centers, forming a one-dimensional chain of { M 2 II ( μ -CN ) 4 M 2 V } squares that crystallize in the monoclinic ( 5, P2 1/ n) and triclinic ( 8, P 1 ¯ ) space groups; 6 ( P2 1/ n) and 10 ( P2 1/ c) crystallize as two-dimensional corrugated sheets containing [ cis-M II(DMF) 4(μ-NC) 2] 2+, [ trans-M II(DMF) 4(μ-NC) 2] 2+, and [M V(CN) 5(μ-CN) 3] 3− units in a 4:2:6 ratio. Magnetic measurements indicate that 6 is a ferrimagnet ( T N = 8 K) that exhibits frequency-dependent behavior in χ″ that is qualitatively similar to 1- and 2-D lattices reported by Tang and Holmes, respectively; dc magnetic measurements suggest that 5, 7, and 8 exhibit incipient magnetic ordering while ac measurements show no frequency-dependent behavior in χ″. Surprisingly, conversion of 5 to 6 in the presence of counterions occurs while heating crystalline samples introduces additional magnetic phases without linkage isomerism; two-dimensional phases containing Mn II centers appear to be the sole product when wet DMF is used as a reaction solvent. The experimental evidence suggests that coordinated DMF ligands are labile and the M II(μ-NC)M V linkages are susceptible to fragmentation.