Anomalous Stoichiometry, 3-D Bridged Triangular/Pentagonal Layered Structured Artificial Antiferromagnet for the Prussian Blue Analogue A₃Mn^II₅(CN)₁₃(A = NMe₄, NEtMe₃). A Cation Adaptive Structure

Abstract

The size of the organic cation dictates both the composition and the extended 3-D structure for hybrid organic/inorganic Prussian blue analogues (PBAs) of A a MnII b (CN) a+2b (A = cation) stoichiometry. Alkali PBAs are typically cubic with both MC6 and M′N6 octahedral coordination sites and the alkali cation content depends on the M and M′ oxidation states. The reaction of MnII(O2CCH3)2 and A+CN– (A = NMe4, NEtMe3) forms a hydrated material of A3MnII 5(CN)13 composition. A3MnII 5(CN)13 forms a complex, 3-D extended structural motif with octahedral and rarely observed square pyramidal and trigonal bipyramidal MnII sites with a single layer motif of three pentagonal and one triangular fused rings. A complex pattern of MnIICN chains bridge the layers. (NMe4)3MnII 5(CN)13 possesses one low-spin octahedral and four high-spin pentacoordinate MnII sites and orders as an antiferromagnet at 11 K due to the layers being bridged and antiferromagnetically coupled by the nonmagnetic cyanides. These are rare examples of intrinsic, chemically prepared and controlled artificial antiferromagnets and have the advantage of having controlled uniform spacing between the layers as they are not physically prepared via deposition methods. A3Mn5(CN)13 (A = NMe4, NEtMe3) along with [NEt4]2MnII 3(CN)8, [NEt4]­MnII 3(CN)7, and Mn­(CN)2 form stoichiometrically related A a MnII b (CN) a+2b (a = 0, b = 1; a = 2, b = 3; a = 1, b = 3; and a = 3, b = 5) series possessing unprecedented stoichiometries and lattice motifs. These unusual structures and stoichiometries are attributed to the very ionic nature of the high-spin N-bonded MnII ion that enables the maximization of the attractive van der Waals interactions via minimization of void space via a reduced ∠MnNC. This A a MnII b (CN) a+2b family of compounds are referred to as being cation adaptive in which size and shape dictate both the stoichiometry and structure.

Ferrimagnetic Ordering and Anomalous Stoichiometry Observed for the Cubic, Extended 3D Prussian Blue Analogues (NEt3Me)2MnII5(CN)12 and (NEt2Me2)2MnII5(CN)12: A Cation‐Adaptive Structure

“…This is blue shifted by 10 cm −1 with respect to free cyanide and is similar in energy to the main absorption in (NEt 4 ) 2 Mn 3 (CN) 8 , [8] but contains an asymmetric tail off the low‐energy side. Compounds 1 and 2 also display sharp ν OH absorptions at 3629 and 3630 cm −1 , respectively, indicative of free, non‐hydrogen‐bonded water or hydroxide, consistent with that reported for (NEt 4 ) 2 Mn 3 (CN) 8 , [8] (NEtMe 3 ) 3 Mn 5 (CN) 13 , [7] and K 2 Mn[Mn(CN) 6 ] [5a] . The observed 7 cm −1 split ν CN doublet also differs from the two strong ν CN absorptions at 2075 and 2049 cm −1 observed for (NEtMe 3 ) 3 Mn 5 (CN) 13 [7] .…”

“…Compounds 1 and 2 also display sharp ν OH absorptions at 3629 and 3630 cm −1 , respectively, indicative of free, non‐hydrogen‐bonded water or hydroxide, consistent with that reported for (NEt 4 ) 2 Mn 3 (CN) 8 , [8] (NEtMe 3 ) 3 Mn 5 (CN) 13 , [7] and K 2 Mn[Mn(CN) 6 ] [5a] . The observed 7 cm −1 split ν CN doublet also differs from the two strong ν CN absorptions at 2075 and 2049 cm −1 observed for (NEtMe 3 ) 3 Mn 5 (CN) 13 [7] . The lack of ν OH absorptions in the 3550–3200 and 1630–1600 cm −1 regions indicate the lack of excess water trapped in the lattice (no H 2 O–H 2 O interactions detected; [11] Figure S1 in the Supporting Information).…”

“…To study the effect of cation size in Prussian blue‐related magnets, and to identify new magnetic materials and structural motifs, we previously investigated larger cations, NMe 4 + , NEtMe 3 + and NEt 4 + to target A 2 Mn II [Mn II (CN) 6 ] [7, 8] . However, these larger cations unexpectedly formed trigonal and hexagonal lattices with completely different topologies, that is, 3D bridged‐layered synthetic/artificial antiferromagnets of (NMe 4 ) 3 Mn II 5 (CN) 13 , [7] (NEtMe 3 )Mn II 5 (CN) 13 , [7] and (NEt 4 )Mn II 3 (CN) 7 , [8] composition, and the layered (2D) (NEt 4 ) 2 Mn II 3 (CN) 8 ferrimagnet [8, 9] . These compounds typically possess adjacent low‐spin ( S= 1/2) and high‐spin ( S= 5/2) Mn II sites that antiferromagnetically couple.…”

The immobilisation and reactivity of Fe(CN)63−/4− in an intrinsically microporous polyamine (PIM-EA-TB)

“…Organic-Prussian blue hybrid materials have been employed in electrochromic devices [40] and films [41,42]. Polymer-Prussian blue hybrid materials have been obtained as 2D nanoarchitectures [13], and tetra-alkylammonium cations have been incorporated into Prussian blue analogues [43].…”

Artificial Antiferromagnets Possessing Extended Zero‐, One‐, Two‐, and Three‐Dimensional Structures

“…Hence, it has a 3D bridged layer network structure and orders as an antiferromagnet with coincidently a 27‐K T c [10] . Similar artificial antiferromagnetic ordering is observed for bridged layered structured A 3 Mn II 5 (CN) 13 (A=NMe 4 , NEtMe 3 ) [16] …”