Room-Temperature Organic-Based Magnet (Tc≈50 °C) Containing Tetracyanobenzene and Hexacarbonylvanadate(−I)

A New Family of High Tc Molecule-Based Magnetic Networks: V[x-ClnPTCE]2·yCH2Cl2 (PTCE = Phenyltricyanoethylene)

Using the structural and electronic tunability of molecules to control magnetism is a central challenge of inorganic chemistry. Herein, a ten-member family of the high-ordering temperature (Tc) molecule-based magnetic coordination networks of the form V[x-ClnPTCE]2·yCH2Cl2 (PTCE = phenyltricyanoethylene, y < 0.5) were synthesized and characterized, where x is (are) the position(s) and n is the number of chlorine substitutions on the phenyl ring. These chlorophenyltricyanoethelenes are tunable analogs of the more commonly investigated tetracyanoethylene (TCNE). Varying the number and position of chlorine substitution around the phenyl ring engendered a family of network solids with significantly different magnetic ordering temperatures ranging from 146 to 285 K. The Tcs of these ferrimagnets were rationalized with the aid of cyclic voltammetry and Density Functional Theory (DFT) calculations.

Characterization of Tetracyanopyridine (TCNPy)-Based Magnets: V[TCNPy]2 ⋅z (CH2 Cl2 ) (Tc =111 K) and V[TCNPy]3 ⋅z (CH2 Cl2 ) (Tc =90 K)

The reaction of 2,3,5,6-tetracyanopyridine (TCNPy) with V(CO)6 in CH2 Cl2 forms new organic-based magnets of V[TCNPy]x ⋅z (CH2 Cl2 ) (x=2, 3) composition. Analysis of the IR spectra suggests that the TCNPy is reduced and coordinated to V(II) sites through the nitriles. V[TCNPy]x order as ferrimagnets with 111 and 90 K Tc values for V[TCNPy]2 and V[TCNPy]3 , respectively. Their respective remanent magnetizations and coercive fields are 1260 and 250 emuOe mol(-1) and 9 and 6 Oe at 5 K, and they exhibit some spin-glass behavior.

Variable coordination of redox-active TCNB in discrete and polymeric ferrocenylcopper(I) complexes: structures and spectroelectrochemical behaviour

1,2,4,5-Tetracyanobenzene (TCNB) was reacted with [Cu(dppf)(CH3CN)2](BF4) and [Cu(dchpf)(CH3CN)](BF4), dppf = 1,1'-bis(diphenylphosphino)ferrocene and dchpf = 1,1'-bis(dicyclohexylphosphino)ferrocene, to produce a heterotetranuclear metallamacrocycle 1, {[Cu(dppf)(μ-TCNB)](BF4)}2, and a heterooctanuclear complex 2, [{Cu(dchpf)}4(μ4-TCNB)](BF4)4. Complex 1 is the first example of a structurally characterised discrete transition metal complex of TCNB. Upon crystallisation attempts, compound 2 formed the structurally identified coordination polymer 3, {[Cu(dchpf)(μ-TCNB)]2(BF4)2}n. Structural and spectroscopic analyses confirmed the redox-innocent behaviour of TCNB in 1, 2 and 3. However, the soluble compounds 1 and 2 could be oxidised and reduced spectroelectrochemically (UV-vis, IR, and EPR). The oxidation occurs invariably at the ferrocene sites without notable splitting of redox potentials. Reduction involves the TCNB bridging ligands to produce radical complexes. As a variably bridging acceptor component of supramolecular structures the TCNB ligand thus adopts an intermediate position between the highly electron transfer-active TCNE, TCNQ and TCNQF4 systems and the numerous redox-innocent bridges.

Tetranuclear Complexes of [Fe(CO)2(C5H5)]+ with TCNX Ligands (TCNX = TCNE, TCNQ, TCNB): Intramolecular Electron Transfer Alternatives in Compounds (μ4-TCNX)[MLn]4

The complexes {(mu4-TCNX)[Fe(CO)2(C5H5)]4}(BF4)4 were prepared as light-sensitive materials from [Fe(CO)2(C5H5) (THF)](BF4) and the corresponding TCNX ligands (TCNE = tetracyanoethene, TCNQ=7,7,8,8-tetracyano-p-quinodimethane, TCNB=1,2,4,5-tetracyanobenzene). Whereas the TCNE and TCNQ complexes are extremely easily reduced species with reduction potentials>+0.3 V vs ferrocenium/ferrocene, the tetranuclear complex of TCNB exhibits a significantly more negative reduction potential at about -1.0 V. Even for the complexes with strongly pi-accepting TCNE and TCNQ, the very positive reduction potentials, the unusually high nitrile stretching frequencies>2235 cm(-1), and the high-energy charge-transfer transitions indicate negligible metal-to-ligand electron transfer in the ground state, corresponding to a largely unperturbed (TCNX degrees)(FeII)4 formulation of oxidation states as caused by orthogonality between the metal-centered HOMO and the pi* LUMO of TCNX. Mössbauer spectroscopy confirms the low-spin iron(II) state, and DFT calculations suggest coplanar TCNE and TCNQ bridging ligands in the complex tetracations. One-electron reduction to the 3+ forms of the TCNE and TCNQ complexes produces EPR spectra which confirm the predominant ligand character of the then singly occupied MO through isotropic g values slightly below 2, in addition to a negligible g anisotropy of frozen solutions at frequencies up to 285 GHz and also through an unusually well-resolved solution X band EPR spectrum of {(mu4-TCNE)[Fe(CO)2(C5H5)]4}3+ which shows the presence of four equivalent [Fe(CO)2(C5H5)]+ moieties through 57Fe and 13C(CO) hyperfine coupling in nonenriched material. DFT calculations reproduce the experimental EPR data. A survey of discrete TCNE and TCNQ complexes [(mu4-TCNX)(MLn)4] exhibits a dichotomy between the systems {(mu4-TCNX)[Fe(CO)2(C5H5)]4}4+ and {(mu4-TCNQ)[Re(CO)3(bpy)]4}4+ with their negligible metal-to-ligand electron transfer and several other compounds of TCNE or TCNQ with Mn, Ru, Os, or Cu complex fragments which display evidence for a strong such interaction, i.e., an appreciable value delta in the formulation {(mu4-TCNXdelta-)[Mx+delta/4Ln]4}. Irreversibility of the first reduction of {(mu4-TCNB)[Fe(CO)2(C5H5)]4}(BF4)4 precluded spectroelectrochemical studies; however, the high-energy CN stretching frequencies and charge transfer absorptions of that TCNB analogue also confirm the exceptional position of the complexes {(mu4-TCNX)[Fe(CO)2(C5H5)]4}(BF4)4.