Endrit Shurdha

Extended Network Thiocyanate- and Tetracyanoethanide-Based First-Row Transition Metal Complexes

Linear chain thiocyanate complexes of M(NCS)(2)(OCMe(2))(2) (M = Fe, Mn, Cr) composition have been prepared and structurally, chemically, and magnetically characterized. Fe(NCS)(2)(OCMe(2))(2) exhibits metamagnetic-like behavior, and orders as an antiferromagnet at 6 K. The Mn and Cr compounds are antiferromagnets with T(c) of 30 and 50 K, respectively, with J/k(B) = -3.5 (-2.4 cm(-1)) and -9.9 K (-6.9 cm(-1)), respectively, when fit to one-dimensional (1-D) Fisher chain model (H = -2JS(i)·S(j)). Co(NCS)(2) was prepared by a new synthetic route, and powder diffraction was used to determine its structure to be a two-dimensional (2-D) layer with μ(N,S,S)-NCS motif, and it is an antiferromagnet (T(c) = 22 K; θ = -33 K for T > 25 K). M(NCS)(2)(OCMe(2))(2) (M = Fe, Mn) and Co(NCS)(2) react with (NBu(4))(TCNE) in dichloromethane to form M(TCNE)[C(4)(CN)(8)](1/2), and in acetone to form M[C(4)(CN)(8)](OCMe(2))(2) (M = Fe, Mn, Co). These materials possess μ(4)-[C(4)(CN)(8)](2-) that form 2-D layered structural motifs, which exhibit weak antiferromagnetic coupling. Co(TCNE)[C(4)(CN)(8)](1/2) behaves as a paramagnet with strong antiferromagnetic coupling (θ = -50 K).

MnII(TCNE)3/2(I3)1/2-A 3D network-structured organic-based magnet and comparison to a 2D analog

Mn{sup II}(TCNE){sub 3/2}(I{sub 3}){sub 1/2} and Mn{sup II}(TCNE)[C{sub 4}(CN){sub 8}]{sub 1/2} [tetracyanoethylene (TCNE)] are organic-based magnets with 3D and 2D extended network structures with vastly different magnetic behavior. They have similar ferrimagnetic coupled layers of Mn{sup II}(TCNE){sup {lg_bullet}-} with different interlayer couplings, which lead, respectively, to net ferrimagnetic (T{sub c} = 171 K) and antiferromagnetic (T{sub c} = 68 K) order.

First Row Transition Metal(II) Thiocyanate Complexes, and Formation of 1-, 2-, and 3-Dimensional Extended Network Structures of M(NCS)2(Solvent)2 (M = Cr, Mn, Co) Composition

The reaction of first row transition M(II) ions with KSCN in various solvents form tetrahedral (NMe4)2[M(II)(NCS)4] (M = Fe, Co), octahedral trans-M(II)(NCS)2(Sol)4 (M = Fe, V, Ni; Sol = MeCN, THF), and K4[M(II)(NCS)6] (M = V, Ni). The reaction of M(NCS)2(OCMe2)2 (M = Cr, Mn) in MeCN and [Co(NCMe)6](BF4)2 and KSCN in acetone and after diffusion of diethyl ether form M(NCS)2(Sol)2 that structurally differ as they form one-dimensional (1-D) (M = Co; Sol = THF), two-dimensional (2-D) (M = Mn; Sol = MeCN), and three-dimensional (3-D) (M = Cr; Sol = MeCN) extended structures. 1-D Co(NCS)2(THF)2 has trans-THFs, while the acetonitriles have a cis geometry for 2- and 3-D M(NCS)2(NCMe)2 (M = Cr, Mn). 2-D Mn(NCS)2(NCMe)2 is best described as Mn(II)(μ(N,N)-NCS)(μ(N,S)-NCS)(NCMe)2 [= Mn2(μ(N,N)-NCS)2(μ(N,S)-NCS)2(NCMe)4] with the latter μ(N,S)-NCS providing the 2-D connectivity. In addition, the reaction of Fe(NCS)2(OCMe2)2 and 7,7,8,8-tetracyanoquino-p-dimethane (TCNQ) forms 2-D structured Fe(II)(NCS)2TCNQ. The magnetic behavior of 1-D Co(NCS)2(THF)2 can be modeled by a 1-D Fisher expression (H = -2JS(i)·S(j)) with g = 2.4 and J/kB = 0.68 K (0.47 cm(-1)) and exhibit weak ferromagnetic coupling. Cr(NCS)2(NCMe)2 and Fe(II)(NCS)2TCNQ magnetically order as antiferromagnets with Tcs of 37 and 29 K, respectively, while Mn(NCS)2(NCMe)2 exhibits strong antiferromagnetic coupling. M(NCS)2(THF)4 and K4[M(NCS)6] (M = V, Ni) are paramagnets with weak coupling between the octahedral metal centers.

Dinuclear [CoII(NCMe)5CoII(NCS) 4] possessing octahedral and tetrahedral CoII sites

The structural and magnetic properties of dinuclear [Co(II)(NCMe)(5)Co(II)(NCS)(4)]·MeCN have been investigated. The structure consists of an octahedral Co(II)(NCMe)(5) center connected to a tetrahedral Co(II)(NCS)(4) center bridged by a μ(1,3)-NCS(-) ligand. The bridging NCS(-) weakly couples the pair of S = (3)/(2) Co(II) spin sites, as evidenced by the magnetic data being best fit by the Curie-Weiss expression with θ = -15.5 K.

A New Conformation With an Extraordinarily Long, 3.04 Å Two-Electron, Six-Center Bond Observed for the π-[TCNE]22− Dimer in [NMe4]2[TCNE]2 (TCNE=Tetracyanoethylene)

[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 Å that is also characteristic of reduced TCNE. The reduced TCNE forms a previously unknown non-eclipsed, centrosymmetric π-[TCNE]2 (2-) dimer with nominal C2 symmetry, 12 sub van der Waals interatomic contacts <3.3 Å, a central intradimer separation of 3.039(3) Å, and comparable intradimer C⋅⋅⋅N distances of 3.050(3) and 2.984(3) Å. The two pairs of central C⋅⋅⋅C atoms form a ∢C-C⋅⋅⋅C-C of 112.6° that is substantially greater than the 0° observed for the eclipsed D2h π-[TCNE]2 (2-) 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]2 (2-) 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]2 (2-) 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 kcal mol(-1) ; H=-2 JSa ⋅Sb ); at the CAS(2,2)/MBMP2 level the triplet is computed to be 9.0 kcal mol(-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 kcal mol(-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.

Symmetrical bis(fulvene) chromophores: model compounds for acceptor–donor–acceptor dye architectures

Four model bis(pentafulvene) chromophores have been prepared with a (fulvene)A–D–A(fulvene) architecture. Conjugation of the central donor group with the pendant fulvene rings was apparent from a single crystal X-ray study of the bis(pentafulvene) with 2,5-dihexyloxyphenyl as the central donor group. UV-Vis results indicated a tunable bandgap in the range of 400–700 nm by varying the nature of the central donor in this series of dyes.

3-(4-Bromo-phen-yl)cyclo-pent-2-en-1-one.

In the title compound, C11H9BrO, the cyclopentenone ring is almost planar with an r.m.s. deviation of 0.0097 Å. The largest inter-ring torsion angles [2.4 (3), 1.3 (3) and 3.53 (2)°] reveal only a very small twist between the rings, and suggest that the two rings are conjugated. The molecule is slightly bowed, as shown by the small dihedral angle between the rings [5.3 (1)°]. The crystal packing pattern consists of parallel sheets that stack parallel to the ac plane. Each sheet consists of molecules that pack side-to-side with the same relative orientation of phenyl and cyclopentenone rings along the a- and c-axis directions. Slipped side-to-side, face-to-face and edge-to-face interactions exist between pairs of sheets with edge-to-edge and edge-to-face O⋯H—C(sp 2) weak hydrogen-bond contacts. A relatively short edge-to-face contact (2.77 Å) also exists between pairs of sheets.