Photoswitchable CuII4Mo^IV and CuII2Mo^IV cyanido-bridged molecules

Abstract

The self-assembly of copper(ii) complexes with two Schiff base ligands: L1 = N and L2 = N and octacyanidomolybdate(iv) ions yields two discrete molecules of odd nuclearity, namely pentametallic [Cu(L1)(py)][Mo(CN)]·14HO (1), CuMo and trimetallic [Cu(L2)][Mo(CN)]·9HO (2), CuMo. Both molecular systems have been characterised structurally and magnetically, revealing a photomagnetic effect. In the case of (1) a metal-to-metal charge transfer (MMCT) mechanism is proposed. The analysis of magnetic interactions in the photogenerated state of (1) assumes the formation of the metastable cluster CuCuMo where metal centres in Mo-CN-Cu linkages are ferromagnetically coupled with J = 104(3) cm. In (2) the increase in the magnetisation is due to the singlet-triplet transition on the Mo centre leading to the formation of the metastable CuMo. The presence of the paramagnetic Mo (S = 1) centre linking the Cu (S = 1/2) centres allows for effective ferromagnetic interaction of 3 paramagnetic centres with coupling constant J = 20.2(7) cm.

Heterotrimetallic Cyanide-Bridged 3d-4d-5d Frameworks Based on a Photomagnetic Secondary Building Unit

“…Moreover, K 4 [Mo IV (CN) 8 ]·2H 2 O itself was found to yield M sat / χT max = 1.5 (Nβ mol)/(cm 3 K) in its metastable S = 1 state resulting from 405 nm irradiation. A similar formation of the S = 1 moiety after the irradiation of [Mo IV (CN) 8 ] 4– was reported before, ,− and we conclude that the observed photomagnetic behavior in 1 results from the spin transition centered on the Mo­(IV) ion and not the charge-transfer-induced photodissociation of the [(NC) 7 Mo IV -CN-Pt IV (NH 3 ) 4 -NC-Mo IV (CN) 7 ] 4– unit. In order to further study the behavior of this photomagnetic SBU, attempts to incorporate it into extended coordination networks were made.…”

“…This small change is in line with the temperature dependence of magnetic susceptibility, which shows consistently higher magnetization level after irradiation as compared to that of the initial state (Figure ). The photoinduced transition is reversible, with the compound relaxing thermally to the initial state after 1 h of thermal relaxation at 250 K. The photomagnetic behavior of compound 3 may originate from three different phenomena: (i) charge transfer within Mo­(IV)–Pt­(IV) pairs , of the Mo–Pt–Mo SBU, (ii) charge transfer between Mo­(IV) and Cu­(II), , and (iii) a spin transition located solely at Mo­(IV). ,− The first mechanism (i) is unlikely to occur, as it was not observed in 1 , and the 450 nm irradiation wavelength is far from the maximum of the Mo­(IV)–Pt­(IV) MMCT band (Figure S20). The electron transfer from octa­cyano­molybdate­(IV) to copper­(II) (ii) is not expected in the discussed material, as no additional MMCT band could be observed in the UV–vis spectrum as compared to starting material 1 .…”

Reversible Single-Crystal-to-Single-Crystal Transformation in Photomagnetic Cyanido-Bridged Cd4M2 Octahedral Molecules

“…Cyanidometallate-based photomagnets can be grouped into one of the two classes: metal-to-metal charge transfer (MMCT) and light-induced excited-spin-state trapping (LIESST). In the case of octacyanidometallates, the MMCT class comprises multidimensional coordination networks based on [M­(CN) 8 ] n − (M = Mo, W) and various 3d metal complexes − with a strong focus on Cu II [Mo IV (CN) 8 ] systems. − The occurrence of the LIESST effect − centered at the octacyanidometallate, on the other hand, was suggested for the first time only recently based on X-ray magnetic circular dichroism (XMCD) studies of the bimetallic complexes [Cu II (Meen) 2 ] 2 [Mo IV (CN) 8 ]· x H 2 O (Meen = N , N ′-dimethylethylenediamine) and [Cu II ­(tren)] 6 ­[Mo IV ­(CN) 8 ]­(ClO 4 ) 8 ·4.5H 2 O [tren = tris­(2-aminoethyl)­amine] . XMCD studies of Cs 0.5 Cu 1.75 [Mo­(CN) 8 ] nanoparticles led to similar conclusions about the LIESST origins of the photomagnetic behavior in some [Mo IV (CN) 8 ]-based compounds.…”

Experimental and theoretical insights into the photomagnetic effects in trinuclear and ionic Cu(ii)–Mo(iv) systems

“…Up to now, photomagnetic processes in Cu(II)-Mo(IV) systems have been considered in terms of two possible mechanisms: metal-to-metal charge transfer (MMCT): paramagnetic Cu II (S = 1/2)⋯Mo IV-LS (S = 0)⋯Cu II (S = 1/2) → ferromagnetic Cu I (S = 0)⋯[Mo V-LS -Cu II ](S total = 1), 27,[29][30][31]33,36,[38][39][40][41]43,44,[46][47][48][49][50][51][52][53][54][55] and a Light-Induced Excited Spin-State Trapping (LIESST) effect on the Mo(IV) centre: paramagnetic Cu II (S = 1/2) ⋯Mo IV-LS (S = 0)⋯Cu II (S = 1/2) → ferromagnetic [Cu II -Mo IV-HS -Cu II ](S total = 2). [27][28][29][31][32][33]35,37,42,45 The latter case may result from the photoinduced formation of an intermediate geometry between the ideal geometries of TDD-8 and SAPR-8 (Fig. 5) 32,35,60 or the photodissociation of the single cyanide leading to a reduction of the coordination number to 7.…”

“…[13][14][15][16][17][18][19][20][21][22][23][24] The greatest successes in developing photomagnetic materials were achieved for octacyanidometallate based systems, 25,26 in particular for copper(II)-molybdenum(IV) ones. 27 Furthermore, it was found that Cu II -Mo IV photomagnetic assemblies can be based on polynuclear molecules, [28][29][30][31][32][33][34][35][36][37][38][39][40][41] chains, 33,[42][43][44] layers 33,[45][46][47] and three-dimensional networks 33,[48][49][50][51][52][53][54][55] with at least one bridging cyanide per single copper(II) centre. Surprisingly, ionic systems with an isolated [Mo(CN) 8 ] 4− anion were not considered, assuming that the photomagnetic phenomenon in Cu II -Mo IV compounds originates from the light-induced MMCT mechanism.…”