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Two new iron(II) neutral complexes of bis(1-methylimidazol-2-yl)ketone (Mebik) with molecular formula [FeII(Mebik)2(NCS)2] (1) and [FeII(Mebik)2(NCSe)2] (2) have been synthesized and characterized by magnetic measurements, single-crystal X-ray diffraction, and solid state UV-vis spectroscopy. The temperature dependent magnetic susceptibility measurements of crystalline samples of both compound show the occurrence of a gradual spin transition centered at T1/2 = 260 K and 326 K, respectively. The crystal structures of both compounds were determined at different temperatures, below and above the transition, in order to detect the structural changes associated with the spin transition. The main structural modifications, when passing from the low-spin to the high-spin form, consist of an important lengthening of the Fe-N(Mebik) and Fe-N (C-S/Se) distances (by ca. 0.20 and 0.18 Å, respectively) and a noticeable variation of the N-Fe-N angles, leading to a more distorted [Fe-N6] octahedron. The spin-transition phenomenon also affects the optical properties, with significant decrease of the intensity of the Metal-to-Ligand charge transfer band upon increasing the temperature. Finally, both complexes exhibit a light-induced excited spin-state trapping under laser light irradiation at low temperature. DFT calculations were also carried out on these complexes in order to rationalize the theoretically predicted magnetic and optical behavior with those of the experimental one. The results clearly highlights the dramatic alteration of the magneto-structural behavior of the tris-chelate [FeII(Mebik)3]2+ spin-crossover complex upon substituting one Mebik with NCS and NCSe ligands.

The synthesis of a series of six thioxo-tetrazane derivatives is reported. The crystal structures of five of these new products and the corresponding oxo-compounds (except the 4,6-dimethylpyrimidyl derivative) including two new crystal structures are also described and compared. The structural data show the importance of the substituent for the intramolecular arrangement while the heteroatom (S, O) does not play any role at this stage: the 2-pyridyl, 4,6-dimethylpyrimidyl and 8-quinolyl groups occupy a pseudo-equatorial position related to the existence of an intramolecular hydrogen bond where the substituent acts as an acceptor. 2-Hydroxyphenyl moieties occupy a pseudo-axial position related to the existence of an intramolecular hydrogen bond where the substituent acts as a donor. In the sole example where an intramolecular hydrogen bond is not present (2-imidazolyl derivatives), the preference for the pseudo-axial conformation is determined by the hyperconjugative effect. In contrast with the intramolecular arrangement, the crystal packing strongly depends on the choice of the heteroatom. It shows noticeable differences related to the variable involvement of CS and CO functions as hydrogen-bond acceptors and the occurrence of π stacking between the molecules. It thus appears that the sulfur atom of the thioxotetrazanes is always involved in hydrogen bonding whereas this is not the case for the oxygen atom of the oxotetrazane analogues. This result contrasts with the statistical treatment of the crystal structures of the Cambridge Structural Database in the urea/thiourea series and could be related to the steric hindrance imposed by the two methyl groups borne by the nitrogen atoms located in the α positions of the CX function (X = S, O). [ABSTRACT FROM AUTHOR]

Unlike p-dithiobenzoquinone (1), which is extremely reactive and has never been isolated, the metal-stabilised p-dithiobenzoquinone [Cp*Ir(η4-C6H4S2)] (2c) was prepared and used as an efficient organometallic linker to construct novel supramolecular assemblies. Treatment of 2c with the electrophilic Pt(ii)(terpy) building blocks produced the supramolecular assembly {[Pt(terpy){Cp*Ir-p-(η4-C6H4S2)}Pt(terpy)][OTf]4}n (3), which was fully characterised and its molecular structure was determined by X-ray crystallography. The structure of 3 revealed the presence of π–π and Pt⋯Pt interactions among individual molecules describing a 1D chain. Complex 3 showed unusual UV/Vis absorption and luminescence behaviour at low temperature, imparted from self-aggregation mediated by π–π and Pt⋯Pt interactions. [ABSTRACT FROM AUTHOR]

The first one-dimensional compounds where [Ln(hfac)3] (Ln = Gd, Tb, Dy) building blocks are bridged by a verdazyl-based radical, namely 3-imidazolyl-1,5-dimethyl-6-oxoverdazyl, were prepared and their structures elucidated; the magnetic properties were measured for all compounds and quantitatively fitted for Ln = Gd(iii) using an alternate chain model leading to J1= −1.58 cm−1and to J2= −0.42 cm−1. [ABSTRACT FROM AUTHOR]