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A novel surface modification approach is taken to cyanide‐sensing by using functionalized cellulose surface that is chemically modified by immobilizing cobalt(II)‐bis‐terpyridine complex on it. The cobalt(II)‐bis‐tpy complex can exhibit selective “naked eye” colorimetric detection of micromolar level cyanide in aqueous solution, where the visible red‐orange color of cobalt(II)‐bis‐tpy complex solution (aqueous) disappears in the presence of cyanide ions. In order to make the sensor more proficient and easy to use, these cobalt(II)‐bis‐tpy molecules are chemically grafted on the surface of microcrystalline cellulose and cellulose paper, which turns the color of functionalized cellulose orange‐red. Both of these colored cellulose powder and paper exhibit color loss in 10⁻⁶maqueous solution of potassium cyanide. This functionalized hybrid inorganic–organic paper offers an easy “dip and detect” cyanide sensing.

 

Herein we report heteroleptic Co( ii ) diimine complexes [Co(H 2 bip) 2 Cl 2 ] ( 1 ), [Co(H 2 bip) 2 Br 2 ] ( 2 ), [Co(H 2 bip) 3 ]Br 2 ·1MeOH ( 3 ) and [Co(H 2 bip) 2 (Me 2 bpy)]Br 2 ·(MeCN) 0.5 ·(H 2 O) 0.25 ( 4 ) (H 2 bip = 2,2′-bi-1,4,5,6-tetrahydropyrimidine, bpy = 2,2′-dipyridyl, Me 2 bpy = 4,4′-Me-2,2′-dipyridyl), purposefully prepared to enable a systematic study of magnetic property changes arising from the increase of overall ligand field from σ/π-donor chlorido ( 1 ) to π-acceptor 4,4′Me-2,2′bpy ( 4 ). The presence of axial and rhombic anisotropy ( D and E ) of these compounds is sufficient to allow 1–4 to show field-induced slow relaxation of magnetization. Interestingly, we found as the effective ligand field is increased in the series, rhombicity ( E / D ) decreases, and the magnetic relaxation profile changes significantly, where relaxation of magnetization at a specific temperature becomes gradually faster. We performed mechanistic analyses of the temperature dependence of magnetic relaxation times considering Orbach relaxation processes, Raman-like relaxation and quantum tunnelling of magnetization (QTM). The effective energy barrier of the Orbach relaxation process ( U eff ) is largest in compound 1 (19.2 cm −1 ) and gradually decreases in the order 1 > 2 > 3 > 4 giving a minimum value in compound 4 (8.3 cm −1 ), where the Raman-like mechanism showed the possibility of different types of phonon activity below and above ∼2.5 K. As a precursor of 1 , the tetrahedral complex [Co(H 2 bip)Cl 2 ] ( 1a ) was also synthesized and structurally and magnetically characterized: this compound exhibits slow relaxation of magnetization under an applied dc field (1800 Oe) with a record slow relaxation time of 3.39 s at 1.8 K. 

For a family of uranium pyrazolylborate complexes, we observe correlations between excited-state mixing and slow relaxation of magnetization for U( iii ) complexes, and U⋯B distances in U( iv ) complexes. 

We report the syntheses and magnetic property characterizations of four mononuclear cobalt( ii ) complex salts featuring a tripodal iminopyridine ligand with external anion receptor groups, [CoL 5-ONHtBu ]X 2 (X = Cl ( 1 ), Br ( 2 ), I ( 3 ) and ClO 4 ( 4 )). While all four salts exhibit anion binding through pendant amide moieties, only in the case of 1 is field-induced slow relaxation of magnetisation observed, whereas in the other salts this phenomenon is absent at the limits of our instrumentation. The effect of chloride inducing a seventh Co–N interaction and concomitant structural distortion is hypothesized as the origin of the observed dynamic magnetic properties observed in 1 . Ab initio computational studies carried out on a 7-coordinate Co( ii ) model species survey the complex interplay of coordination number and trigonal twisting on the sign and magnitude of the axial anisotropy parameter ( D ), and identify structural features whose distortions can trigger large switches in the sign and magnitude of magnetic anisotropy.