Thermochromic nitro–nitrito interconversion mediated by weak-linked amide in nickel (II) diaminodiamide complexes in the solid state

Exploring Photoswitchable Properties of Two Nitro Nickel(II) Complexes with (N,N,O)-Donor Ligands and Their Copper(II) Analogues

“…The analyzed nickel complexes exist majorly as the nitro form (η 1 -N­(O) 2 ), whereas their copper equivalents exist exclusively as the κ-nitrito linkage isomer (η 2 -O,ON) in the ground-state crystal structure. These findings are in agreement with the previous literature reports. ,,,, It should also be noted here that solely in the case of the Ni-2a crystal structure do two isomeric forms, namely nitro and endo -nitrito (η 1 -ONO), coexist with 92(1)% and 8(1)% occupancies at 100 K, respectively (keeping in mind that no 100 K data were collected for Ni-2b due to crystal degradation). In order to verify the impact of temperature on the relative populations of both linkage isomers, multi-temperature X-ray diffraction experiments were performed.…”

“…Solid-state infrared (IR) multi-temperature spectroscopic experiments, also performed after the sample was irradiated with LED light, were conducted to determine the optimal isomerization reaction conditions for each of the four systems under consideration and to estimate the achievable conversion in the case of thin-film samples (their purity and composition were confirmed by elemental analyses and PXRD patterns; for the latter, see the Supporting Information). Special attention was paid to vibrational bands present in the 500–850 and 1000–1500 cm –1 spectral ranges, as according to literature crucial vibrations of the ONO species should appear in these regions. ,,− The obtained experimental results were supported by theoretically predicted normal-mode frequencies computed at the DFT­(B3LYP)/6-311++G** level of theory (Figures 6S and 7S and Table 8S).…”

An optically reversible room-temperature solid-state cobalt(iii) photoswitch based on nitro-to-nitrito linkage isomerism

“…It should be noted that there are also examples of nickel( ii ) complexes undergoing reversible nitro-to-nitrito conversion at higher temperatures, such as the simple [Ni(C 6 H 4 (NH 2 ) 2 ) 2 (NO 2 )] complex exhibiting thermally induced switching in the 383–393 K temperature range, 27 which is accompanied by a colour change. Also, [Ni(C 8 H 18 N 4 O 2 )(NO 2 ) 2 ]·H 2 O exhibits similar properties, switching reversibly from the nitro to the exo -nitrito form with colour change while heating from 298 to 383 K. 28 In both cases the process was confirmed spectroscopically.…”

Photogeneration of Several Linkage Isomers and Investigation of Forward and Backward Nitro-Nitrito Isomerization Processes in a Palladium Complex

“…PLIs of the nitrite ligand can be generated by light with different wavelengths in the range of 350–650 nm. ,, In general, in these systems a backward reaction M-ONO → M-NO 2 is accessible only by heating, i.e., nitrito PLIs are metastable states; however, there are two examples of partial light-induced backward reaction in case of [Co­(Me-dpt)­(NO 2 ) 3 ] (Me-dpt = 3,3′-diamino- N -methylpropanediamine) and ruthenium complex trans -[Ru­(py) 4 (NO 2 ) 2 ] (py = pyridine). , The degree of metastability is governed by the height of the activation barrier, − and in practice the majority of nitrito PLIs are stable at temperatures below 300 K. ,, Nevertheless, there are several examples of complexes exhibiting much higher thermal stability at room temperature, such as mentioned above cobalt complex or platinum compound trans -[Pt­(PCy 3 ) 2 (NO 2 ) 2 ] (PCy 3 = tricyclohexylphosphine). , The forward nitro-nitrito isomerization might be thermally induced at high temperature (≈400 K) as well, which was shown for nickel complexes. , …”