Photocrystallographic identification of metastable nitrito linkage isomers in a series of nickel(ii) complexes

Abstract

Single crystal photocrystallographic experiments and solid state Raman spectroscopy have been used to determine the low temperature, metastable structures of the nickel(ii) nitrito complexes [Ni(aep)(2)(η(1)-ONO)(2)] 1#O (aep = 1-(2-aminoethyl)piperidine), [Ni(aem)(2)(η(1)-ONO)(2)] 2#O (aem = 1-(2-aminoethyl)morpholine), and [Ni(aepy)(2)(η(1)-ONO)(2)] 3#O (aepy = 1-(2-aminoethyl)pyrrolidine and where the #O denotes the oxygen-bound nitrito metastable molecule). These linkage isomers of the equivalent nitro complexes [Ni(aep)(2)(η(1)-NO(2))(2)] 1, [Ni(aem)(2)(η(1)-NO(2))(2)] 2 and [Ni(aepy)(2)(η(1)-NO(2))(2)] 3 are formed by LED irradiation at temperatures below 120 K. The behavior of the three complexes upon irradiation is generally similar, but some subtle differences have been observed. From the crystallographic studies all three complexes 1-3 exhibit the endo-nitrito linkage isomer upon irradiation, however, for 3# (a crystal structure that contains components of both 3 and 3#O) an exo-nitrito isomer is also observed. Under conditions of 90-100 K, with blue light, the conversion percentages to the nitrito isomers, 1#O, 2#O and 3#O were 16%, 22% and 30%, respectively. At temperatures below 110 K all three nitrito isomers were stable for over four hours but while 2#O and 3#O could be detected at temperatures down to 30 K, at temperatures below 60 K the metastable structure 1#O appeared to be quenched and only the nitro isomer 1 was identified in the crystal. The solid state Raman spectra for 1#, 2# and 3# confirmed the photocrystallographic results with the nitrito isomers being identified from the O-N-O deformation vibrations.

Photoactivated linkage isomerism in single crystals of nickel, palladium and platinum di-nitro complexes – a photocrystallographic investigation

“…In our efforts to gain a more complete understanding of the photochemical reaction in such systems we have investigated a number of transition metal complexes exhibiting solid-state nitro-nitrito linkage isomerism. As a result of studies aimed 70 at improving photoconversion levels we reported the first fully-reversible nitronitrito isomerism in the complex [Ni(dppe)(η 1 15 In addition we have reported the interesting behaviour of the tridentate amine complex [Ni(Et 4 dien)(η 1 -NO 2 ) 2 ], which undergoes reversible nitro-nitrito linkage isomerism following exposure to both UV light and heat, 16 and have also observed similar behaviour in the system [Pd(papaverine)(PPh 3 )(NO 2 )] on exposure to both of these stimuli. 17 These results indicate that the nature of the surrounding crystalline environment has an effect on the photochemical reaction, in-line with previous findings.…”

The lighter side of MOFs: structurally photoresponsive metal–organic frameworks

“…We have direct experience of this approach as both a means to produce photoresponsive single crystals to examine the photoreactivity of particular chromophores in a framework environment, and to make materials with which to develop and demonstrate the emerging field of X-ray photocrystallography. [77][78][79][80][81][82][83][84][85][86][87][88][89] In 2009 we reported a combined spectroscopic and crystallographic study on the [Mn(DMF)2[LM(CO)3Cl]]∞ L = , -bipyridine-5,5-dicarboxylate; M = Re (ReMn) or M = Mn (MnMn)) which contains an (M(diimine)(CO)3Cl) unit as the linker, with the CO groups facially coordinated, combined with Mn nodes to form the 3D structure. 82 Ultrafast time-resolved FTIR and spatially resolved Raman mapping were used to characterise the short-lived excited states (picosecondnanosecond) of the parent facisomer and to determine the conditions required for photoinduced fac-mer isomerisation to occur.…”

Chemical Crystallography at the Advanced Light Source

“…The conversion rate varied from 16% for endo-Ni(aep)(ONO) 2 after exposure to 470 nm light, to 46% for endo-Pd(PPh 3 ) 2 (ONO) 2 after exposure to 362 nm light (up from 30% using 400 nm light). In addition to displaying lower nitrite to nitrito conversion, the nitrito anions in Ni(aepy)(ONO) 2 Partial conversions could be obtained by illumination of Ni(aep)(NO2)2, Ni(aepy)(NO2)2 (aep = 1-(2-aminoethyl)piperidine, aepy = 1-(2-aminoethyl)pyrrolidine) [55], Pd(PPh3)2(NO2)2 and Pd(AsPh3)2(NO2)2 [56] (Figure 6). The conversion rate varied from 16% for endo-Ni(aep)(ONO)2 after exposure to 470 nm light, to 46% for endo-Pd(PPh3)2(ONO)2 after exposure to 362 nm light (up from 30% using 400 nm light).…”

“…Partial conversions could be obtained by illumination of Ni(aep)(NO 2 ) 2 , Ni(aepy)(NO 2 ) 2 (aep = 1-(2-aminoethyl)piperidine, aepy = 1-(2-aminoethyl)pyrrolidine) [55], Pd(PPh 3 ) 2 (NO 2 ) 2 and Pd(AsPh 3 ) 2 (NO 2 ) 2 [56] (Figure 6). The conversion rate varied from 16% for endo-Ni(aep)(ONO) 2 after exposure to 470 nm light, to 46% for endo-Pd(PPh 3 ) 2 (ONO) 2 after exposure to 362 nm light (up from 30% using 400 nm light).…”

“…2 . Generated from data contained in [55] and [56]. In all cases, residual nitro ligands are shown using blue bonds and hollow atoms; exo-nitrito ligands (if any) are shown with green bonds and striped atoms, while endo-nitrito ligands are shown using red bonds and hatched atoms or gold bonds with solid atoms.…”