Variations in topology and magnetic properties of hepta- and octacyanometallates of molybdenum with manganese(ii)

Abstract

Treatment of [Mn(dpop)(H₂O)₂]Cl₂ (dpop = 2,13-dimethyl-3,6,9,12,18-pentaazabicyclo-[12.3.1]octadeca-1(18),2,12,14,16-pentaene) with K₄[Mo(CN)₇]·2H₂O under varied synthetic conditions afforded four different compounds: {[Mn(dpop)]₄[(dpop)Mn(H₂O)]₂[Mo^III(CN)₇]₃·27H₂O}_n (1), {[(dpop)Mn(H₂O)][Mo^III(CN)₇][Mn(dpop)]₃[Mo^IV(CN)₈]·29H₂O}_n (2), {[(dpop)Mn(H₂O)]₂[Mo^IV(CN)₈]₂[Mn(dpop)]₄[Mo^III(CN)₇]·12H₂O}_n (3), and [(dpop)Mn(H₂O)]₂[Mo^IV(CN)₈]·9H₂O (4). Compound 1 contains only [Mo^III(CN)₇]⁴⁻ anions and exhibits a corrugated two-dimensional layered architecture. The structure of 2 with a 1 : 1 ratio of Mo^III : Mo^IV is best described as a ladder-like chain composed of [Mo^III(CN)₇]⁴⁻-based pentanuclear [Mo^IIIMn^II₄] fragments which are further linked by in situ produced [Mo^IV(CN)₈]⁴⁻ anions. In the case of 3, [Mn₈Mo₈] rings containing bent [Mo^IIIMn^II₂] fragments are extended into a two-dimensional layer with the ratio of [Mo(CN)₇]⁴⁻ : [Mo(CN)₈]⁴⁻ being 1 : 2. Compound 4 exhibits a bent trinuclear structure in which two CN⁻ groups of [Mo(CN)₈]⁴⁻ function as μ₂-bridges to [Mn(dpop)(H₂O)]²⁺ fragments. Magnetic studies suggest significant antiferromagnetic coupling interactions occur between Mo(III) and Mn(II) ions while, not surprisingly, interactions between the Mn(II) ions through diamagnetic [Mo^IV(CN)₈]⁴⁻ anions are negligible. Compound 1 exhibits ferrimagnetic ordering below 3.0 K whereas 2 shows the signature of single molecule magnet behavior with slow relaxation of the magnetization and an effective energy barrier (U_eff) of 8.1 K.