We present here the efficient microwave-assisted synthesis and photophysical study of a family of ruthenium(II) complexes of the general formula [Ru(bpy)x(qpy)3-x]2+ (where bpy = 2,2′-bipyridine, qpy = 4,4′:2′,2″:4″,4‴-quaterpyridine, and x = 0, 1, 2 giving compounds 1 = [Ru(bpy)2(qpy)1]2+, 2 = [Ru(bpy)1(qpy)2]2+, and 3 = [Ru(qpy)3]2+). Compared to the standard reference, [Ru(bpy)3]2+ (τ = 870 ns, Φ = 9.5%), the complexes display longer-lived excited state lifetimes at room temperature (τ: 1 = 1440 ns, 2 = 1640 ns, 3 = 1780 ns) and improved quantum yields (Φ: 1 = 14%, 2 = 19%, 3 = 23%). Theoretical calculations were performed to support the interpretation of these photophysical properties. These complexes are excellent photosensitizers as they absorb light throughout the visible spectrum, have excellent excited state lifetimes at room temperature, and have high quantum yields. In combination with a cobalt dimethylglyoxime catalyst, they exhibit remarkable hydrogen evolution with blue light, and they are far more efficient than the reference in the field, [Ru(bpy)3]2+.

A high-nuclearity metal-cyanide cluster [Mo6Cu14] has been prepared and its photomagnetic properties investigated. The photoswitchable magnetic phenomenon observed is thermally reversible (T ≈ 230 K). In the field of photomagnetism, [Mo6Cu14] represents a unique example of a nanocage and the highest nuclearity observed so far.

Photo-induced spin transition in a molybdenum–zinc complex has been evidenced and fully characterized by Squid magnetometry and several spectroscopies performed under irradiation (IR, EPR, etc.). The phenomenon has been confirmed by X-ray diffraction and DFT calculations yielding a Light-Induced Excited Spin State Trapping Effect (LIESST) on a 4d transition metal ion.

A high-temperature, microwave synthesis of [Ru(qpy)3]2+ (qpy = 4,4′:2′,2′′:4′′,4′′′-quaterpyridine) affords the photosensitiser in quantitative yield. The complex produces H2 photocatalytically in a range extending from the UV region of the spectrum to the red with greater efficiency when compared to [Ru(bpy)3]2+.

A new family of hetero-tri-metallic complexes [M(CuTb)]n (MIII = Co, Cr, Fe; n = 1, 2, ∞), composed of three series of three compounds (oligo- and poly-nuclear complexes based on [Cu–Tb] subunits), is presented and fully characterized. These nine compounds, viewed as different assemblies of single-molecule magnet (SMM) building blocks, connected to various hexacyanometalate centers, illustrate how the SMM behavior of the [CuTb] moiety can be modulated via the control of intermolecular interactions. Specifically, the combination of the “non-innocent” diamagnetic [CoIII(CN)6]3− center with a [Cu–Tb]3+ moiety enabled isolation of the magnetic entities, resulting in an improvement of the SMM behavior (ranging from Ueff = 5–7 cm−1 to 15–17 cm−1).

Two types of cyanide bridged molybdenum–copper photomagnetic films have been obtained: the first one is based on a molecular [MoCu6] complex, the other being a two-dimensional [MoCu2] coordination network. Both systems employ surfactant functionalized ligands and films were deposited on Melinex substrates using the Langmuir–Blodgett technique. All systems, including monolayer films, showed full retention of the intrinsic photomagnetic properties known for analogous solids as demonstrated by EPR spectroscopy.

Hetero-tetra-metallic species based on hexanuclear assemblies [((valen)M1)Ln(OH2)2(μM2(CN)8)]22− (Ln = GdIII, TbIII; M1 = CuII, NiII and M2 = MoIV, WIV) and co-crystallized mononuclear complexes [M3(tpy)2]2+ (M3 = NiII, RuII, OsII) were identified, fully characterized, and shown to constitute a new class of single-molecule magnets.

The synthesis, the structural characterization and the magnetic properties of a heterotrimetallic decanuclear square, [(Mo(CN)8)2(CuLTb)4)]4+, noted MoCuTb, are described. This supramolecular compound, viewed as the first example of a metal-capped square, behaves as a single molecule magnet with a magnetic anisotropic barrier energy of Ueff = 13.40 cm−1 (19.25 K).

Recently synthesized copper octacyanomolybdate molecules present interesting photomagnetic properties. Before irradiation, the molecules behave as noncoupled CuII paramagnetic ions (with central diamagnetic MoIV ion), whereas after irradiation (406 nm) they behave as superparamagnetic molecules with CuII ions coupled to the molybdenum ion. The proposed mechanism to explain these photomagnetic properties is based on the photoinduced charge transfer from MoIV (S = 0) to CuII (S = 1/2) leading to the formation of MoV (S = 1/2) and CuI (S = 0) with strong ferromagnetic coupling between MoV and the other CuII spin carriers. This paper presents X-ray magnetic circular dichroism (XMCD) measurements at the molybdenum L2,3 edges. Two bimetallic molecules have been investigated: [Mo(CN)2(CN-CuL)6]8+, L being tris(2-amino)ethylamine and [Mo(CN)6(CN-CuL′2)2], with L′ being N,N′,dimethyl ethylene diamine (labeled MoCu2-Meen). In both cases, before irradiation the XMCD signal is null as expected for diamagnetic MoIV (S = 0). After irradiation, an XMCD signal appears, which directly demonstrates the formation of spin density on the Mo ion. After reaching room temperature, the photoinduced spectral features disappear, indicating the reversibility of the photoinduced process. In the case of MoCu2-Meen, the XMCD experiments allow the observation of an X-ray-induced metastable state made of high-spin MoIV ion (S = 1). The application of the sum rule for isotropic spectra shows that there is no variation of the molybdenum oxidation state during the X-ray-induced magnetic process. From the Mo L2,3 XMCD signal of the X-ray-photoexcited MoCu2-Meen, we obtain an orbital magnetic moment equal to 0.13 μB and a spin magnetic moment equal to 1.22 μB at T = 10 K and H = 6 T. These results demonstrate that the Mo ion in the X-ray-photoinduced excited state of the MoCu2-Meen complex is high-spin MoIV (S = 1).

Taking into account the general interest in photoswitchable nanomagnets, we present an original synthetic route to well-defined photoswitchable heterotrimetallic complexes. Our strategy demonstrates the feasibility of using a “molybdenum−copper” switchable complex with terminal cyanide ligands as relevant synthons for the rational design and synthesis of heterotrimetallic photoswitchable molecular architectures. Starting from a pentanuclear compound based on an octacyanometalated precursor, [MoIV(CN)4(CNCuII(Me2en)2)4]4+, and a [NiII(cyclam)]2+ assembling building block, we succeeded in synthesizing a photoswitchable heterotrimetallic chain, denoted as {NiMo2Cu7}n. The compound has been characterized by single-crystal X-ray diffraction, UV−vis and IR spectroscopies, and powder magnetic and photomagnetic susceptibility measurements. Before irradiation, the compound behaves as a paramagnet with eight independent spin carriers (CuII d9, S = 1/2, and NiII d8, S = 1). After irradiation, a long-lived metastable state persists until relatively high temperature (120 K) and is thermally reversible.

Photomagnetism in molecular systems is a new development in molecular magnetism. It traces back to 1982 and 1984 when a transient effect and then the light-induced excited-spin-state-trapping effect was discovered in spin-crossover complexes. The present contribution gives a definition of the phenomenon, a process that changes the magnetism of a (molecular) system after absorption of a photon. It is limited to the discussion of photomagnetism based on metal−metal electron transfer in clusters and extended molecule-based magnets. The paper is organized around the main pairs of spin bearers, which allowed us to evidence and to study the phenomenon: Cu−Mo, Co−Fe, and Co−W. For each metallic pair, we report and discuss the conditions of appearance of the effect and its characteristics, both in extended structures and in molecular units: structure, spectroscopy, magnetism, thermodynamics and kinetics, and applications. We conclude with some brief prospects. The field is in rapid expansion. We are convinced that the interaction of photons with magnetized matter, to provide original magnetic properties, will meet more and more interest in the future.

Numerous μ-cyanido bridged polynuclear complexes, [M(CN)n(CNCuIIL)6−n]m+ (with M = CrIII or CoIII, n = 0–5 and L = tris(2-amino)ethylamine (tren) or N,N-dimethylethylenediamine (Me2en)), have been synthesised: [CoIII(CN)5{CNCuII(Me2en)2}]−, [CoIII(CN)4(CNCuIItren)2]+/[CoIII(CN)3(CNCuIItren)3]3+, [{CoIII(CN)6}2{CuII(Me2en)2}5]4+ and [CoIII(CNCuIItren)6]9+ denoted correspondingly CoCu, CoCu2/CoCu3, Co2Cu5 and CoCu6 as well as chromium derivatives: [CrIII(CN)5{CNCuII(Me2en)2}]−, cis-[CrIII(CN)2{CNCuII(Me2en)2}4]5+, trans-[CrIII(CN)2{CNCuII(Me2en)2}4]5+ and [CrIII(CNCuIItren)6]9+ denoted CrCu, ciscisciscisciscis-CrCu4, transtranstranstranstrans-CrCu4 and CrCu6, respectively. All compounds have been characterised by IR spectroscopy and most of them by X-ray crystallography. The magnetic properties of the complexes have been studied and the spin and the anisotropy values as well as the intra- and inter-molecular exchange couplings evaluated. For the cobalt centred species, in first approximation, the complexes behave as one, five and six isolated copper(II) complexes, but more accurate studies allow us to evaluate the weak antiferromagnetic coupling constant between two next-nearest neighbours Cu–Co(III)–Cu. For the chromium centred species, the spin state varies from 1 to 9/2 (with ferromagnetic interaction for transtranstranstranstrans-CrCu4 and CrCu6 and weak antiferromagnetic interaction for CrCu and ciscisciscisciscis-CrCu4) with a negligible effective anisotropic factor. Experimentally, the exchange coupling between the μ-cyanido bridged spin carriers Cr(III) and Cu(II) varies from −2.5 to +45 cm−1 increasing with the C–N–Cu angle. A magneto–structural correlation allows us to rationalise the most relevant features of the exchange interaction between Cr(III) and Cu(II) through a cyanido bridge.

Hetero-tetra-metallic species based on hexanuclear assemblies [((valen)M1)Ln(OH2)2(μM2(CN)8)]22− (Ln = GdIII, TbIII; M1 = CuII, NiII and M2 = MoIV, WIV) and co-crystallized mononuclear complexes [M3(tpy)2]2+ (M3 = NiII, RuII, OsII) were identified, fully characterized, and shown to constitute a new class of single-molecule magnets.

Photo-induced spin transition in a molybdenum–zinc complex has been evidenced and fully characterized by Squid magnetometry and several spectroscopies performed under irradiation (IR, EPR, etc.). The phenomenon has been confirmed by X-ray diffraction and DFT calculations yielding a Light-Induced Excited Spin State Trapping Effect (LIESST) on a 4d transition metal ion.

A new family of hetero-tri-metallic complexes [M(CuTb)]n (MIII = Co, Cr, Fe; n = 1, 2, ∞), composed of three series of three compounds (oligo- and poly-nuclear complexes based on [Cu–Tb] subunits), is presented and fully characterized. These nine compounds, viewed as different assemblies of single-molecule magnet (SMM) building blocks, connected to various hexacyanometalate centers, illustrate how the SMM behavior of the [CuTb] moiety can be modulated via the control of intermolecular interactions. Specifically, the combination of the “non-innocent” diamagnetic [CoIII(CN)6]3− center with a [Cu–Tb]3+ moiety enabled isolation of the magnetic entities, resulting in an improvement of the SMM behavior (ranging from Ueff = 5–7 cm−1 to 15–17 cm−1).

A high-nuclearity metal-cyanide cluster [Mo6Cu14] has been prepared and its photomagnetic properties investigated. The photoswitchable magnetic phenomenon observed is thermally reversible (T ≈ 230 K). In the field of photomagnetism, [Mo6Cu14] represents a unique example of a nanocage and the highest nuclearity observed so far.

The synthesis, the structural characterization and the magnetic properties of a heterotrimetallic decanuclear square, [(Mo(CN)8)2(CuLTb)4)]4+, noted MoCuTb, are described. This supramolecular compound, viewed as the first example of a metal-capped square, behaves as a single molecule magnet with a magnetic anisotropic barrier energy of Ueff = 13.40 cm−1 (19.25 K).

A high-temperature, microwave synthesis of [Ru(qpy)3]2+ (qpy = 4,4′:2′,2′′:4′′,4′′′-quaterpyridine) affords the photosensitiser in quantitative yield. The complex produces H2 photocatalytically in a range extending from the UV region of the spectrum to the red with greater efficiency when compared to [Ru(bpy)3]2+.