23237-02-7Relevant articles and documents
Anomalous Stoichiometry, 3-D Bridged Triangular/Pentagonal Layered Structured Artificial Antiferromagnet for the Prussian Blue Analogue A3MnII5(CN)13 (A = NMe4, NEtMe3). A Cation Adaptive Structure
Lapidus, Saul H.,Graham, Adora G.,Kareis, Christopher M.,Hawkins, Casey G.,Stephens, Peter W.,Miller, Joel S.
, p. 911 - 921 (2019)
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 AaMnIIb(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 A3MnII5(CN)13 composition. A3MnII5(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)3MnII5(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]2MnII3(CN)8, [NEt4]MnII3(CN)7, and Mn(CN)2 form stoichiometrically related AaMnIIb(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 aMnIIb(CN)a+2b family of compounds are referred to as being cation adaptive in which size and shape dictate both the stoichiometry and structure.
A New Conformation with an Extraordinarily Long, 3.04 ? Two-Electron, Six-Center Bond Observed for the π-[TCNE]22- Dimer in [NMe4]2[TCNE]2 (TCNE=Tetracyanoethylene)
Graham, Adora G.,Mota, Fernando,Shurdha, Endrit,Rheingold, Arnold L.,Novoa, Juan J.,Miller, Joel S.
, p. 13240 - 13245 (2015)
[NMe4]2[TCNE]2 (TCNE=tetracyanoethenide) formed from the reaction of TCNE and (NMe4)CN in MeCN has νCN IR absorptions at 2195, 2191, 2172, and 2156 cm-1 and a νCC absorption at 1383 cm-1 that are characteristic of reduced TCNE. The TCNEs have an average central C-C distance of 1.423 ? that is also characteristic of reduced TCNE. The reduced TCNE forms a previously unknown non-eclipsed, centrosymmetric π-[TCNE]22- dimer with nominal C2 symmetry, 12 sub van der Waals interatomic contacts 2h π-[TCNE]22- dimer possessing a two-electron, four-center (2e-/4c) bond with two C?C components from a molecular orbital (MO) analysis. A MO study combining CAS(2,2)/MRMP2/cc-pVTZ and atoms-in-molecules (AIM) calculations indicates that the non-eclipsed, C2 π-[TCNE]22- dimer exhibits a new type of a long, intradimer bond involving one strong C?C and two weak C?N components, that is, a 2e-/6c bond. The C2 π-[TCNE]22- conformer has a singlet, diamagnetic ground state with a thermally populated triplet excited state with J/kB=1000 K (700 cm-1; 86.8 meV; 2.00 kcalmol-1; H=-2JSa·Sb); at the CAS(2,2)/MBMP2 level the triplet is computed to be 9.0 kcalmol-1 higher in energy than the closed-shell singlet ground state. The results from CAS(2,2)/NEVPT2/cc-pVTZ calculations indicate that the C2 and D2h conformers have two different local metastable minima with the C2 conformer being 1.3 kcalmol-1 less stable. The different natures of the C2 and D2h conformers are also noted from the results of valence bond (VB) qualitative diagram that shows a 10e-/6c bond with one C?C and two C?N bonding components for the C2 conformer as compared to the 6e-/4c bond for the D2h conformer with two C?C bonding components. C2 or D2h? That is the question: The C2 conformation of π-[TCNE]22- observed in [NMe4]2[TCNE] (see figure) differs significantly from the eclipsed, D2h conformation reported for about 30 other cations. The C2 conformation is computed to be 1.3 kcalmol-1 less stable than the D2h conformation, and both conformations are minima in their potential energy surfaces.
