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The syntheses and magnetic properties of two new isostructural tetranuclear lanthanide complexes, [Ln 4 (N 3 ) 4 (Tpz) 8 ] (Ln = Gd III ( 1 ), Dy III ( 2 ) and, Tpz = tris(pyrazolyl)borate) are reported. In these complexes the lanthanide ions are eight coordinate with distorted geometries and are bridged by end-to-end azido ligands in a rare rhombus topology. Direct current magnetic susceptibility studies revealed the presence of weak ferromagnetic exchange interactions between the metal ions which were quantified in the case of the isotropic Gd 4 analog to give J  = 0.0080(2) cm −1 and g  = 2.01(1). Complex 2 exhibits frequency and temperature dependent out-of-phase ( χ ″) ac magnetic susceptibility signals under a 0.1 T applied field, suggestive of SMM behavior. Low temperature magnetization studies revealed that compound 1 exhibits an appreciable magnetic entropy change, −Δ S m , which reaches a value of ∼20.9 J kg −1  K −1 at T  = 3 K for Δ H  = 7 T. Theoretical calculations further support the experimental results. [ABSTRACT FROM AUTHOR]

The initial use of quinoline-2-aldoxime (qaoH) and 2,6-diacetylpyridine dioxime (dapdoH 2 ) in heterometallic Mn–Ca chemistry has afforded a mixed-valence {Mn II/III 22 Ca 2 } cluster containing several {Mn 4 CaO x } subunits and a ‘butterfly’-like {Mn IV 2 Ca 2 } complex, respectively. The one-pot reaction of Mn(O 2 CPh) 2 ·2H 2 O and Ca(O 2 CPh) 2 ·H 2 O with qaoH and NEt 3 in a 1:1:1:1 molar ratio in a solvent mixture comprising MeCN/MeOH gave complex [Mn 22 Ca 2 O 14 (OH) 4 (OMe) 6 (O 2 CPh) 22 (qao) 2 (MeCN) 2 (H 2 O) 4 ](OH) 2 ( 1 ; 6Mn II /16Mn III ) in 20% yield. A similar reaction with that of 1 , albeit with Mn(O 2 CPh) 2 ·2H 2 O and Ca(NO 3 ) 2 ·4H 2 O in the presence of dapdoH 2 and NEt 3 , in a molar ratio of 1:1:2:2 in MeCN/MeOH, led to the smaller nuclearity complex [Mn 2 Ca 2 (OMe) 2 (NO 3 ) 2 (dapdo) 4 ] ( 2 ; 2Mn IV ) in 40% yield. The reported compounds demonstrate structural and magnetic relevance to both low- and high-valent states of the OEC. [ABSTRACT FROM AUTHOR]

The employment of cyanato (OCN − ) group in high oxidation state manganese cluster chemistry, in conjunction with carboxylate ions and the organic chelating/bridging ligand 2-(hydroxymethyl)pyridine (hmpH), is reported. The syntheses, crystal structures, and magnetochemical characterization are described for [Mn 16 O 8 (OR) 4 (OCN) 4 (O 2 CMe) 12 (hmp) 6 (ROH) 2 ] (R = Me ( 1 ), Et ( 2 )) and [Mn 18 O 14 (O 2 CR) 18 (hmp) 4 (hmpH) 2 (H 2 O) 2 ] (R = Me ( 3 ), Et ( 4 )). The 2:1:1:1 reactions of Mn(O 2 CMe) 2 ·4H 2 O, hmpH, NaOCN and NEt 3 in solvent MeOH or EtOH afford the isostructural complexes [Mn 16 O 8 (OR) 4 (OCN) 4 (O 2 CMe) 12 (hmp) 6 (ROH) 2 ] (R = Me ( 1 ), Et ( 2 )). The [Mn 16 (μ 4 -O) 4 (μ 3 -O) 4 (μ-OMe) 4 (μ 3 -OR) 6 (μ-OR) 6 ] 10+ core of representative complex 1 comprises a Mn II 4 Mn III 4 double-cubane subunit attached on either side to two symmetry-related Mn II Mn III 3 defective dicubanes. A similar reaction of Mn(O 2 CR) 2 ·4H 2 O, hmpH, NaOCN and NEt 3 , but in solvent MeCN, led instead to the formation of [Mn 18 O 14 (O 2 CR) 18 (hmp) 4 (hmpH) 2 (H 2 O) 2 ] (R = Me ( 3 ), Et ( 4 )). Compounds 3 and 4 are very similar to each other and can be described as a central [Mn III 4 (μ-O) 6 ] rodlike subunit attached on either side to two symmetry-related [Mn 7 O 9 ] subunits. Variable-temperature, solid-state dc and ac magnetic susceptibility studies revealed the presence of predominant antiferromagnetic exchange interactions in all compounds, and possible S = 2 or 1 (for 1 and 2 ) and S = 0 (for 3 and 4 ) ground state spin values. The combined results demonstrate the ability of cyanato groups to facilitate the formation of new polynuclear Mn II/III complexes with structures different than these obtained from the use of the related azides. [ABSTRACT FROM AUTHOR]

Abstract: The combination of azide, carboxylate (pivalate and in situ generated formate) and triethanolamine ligands in higher oxidation state Mn cluster chemistry has afforded a new pentadecanuclear, mixed-valence(II,III) compound with a large S and a negative D value. The unprecedented [MnII 2MnIII 13] cluster exhibits frequency-dependent out-of-phase (χ M″) signals, characteristics of the superparamagnetic-like slow relaxation of an SMM. [Copyright &y& Elsevier]

Abstract: The use of pyridine-2,6-dimethanol (pdmH2) in copper(II) nitrate chemistry is reported. The reaction of Cu(NO3)2·3H2O with one equivalent of pdmH2 in MeCN affords the known mononuclear complex [Cu(pdmH2)2](NO3)2 (1) in high-yield. The reaction of 1 and NaOMe in an 1:1 ratio, as well as the reaction between Cu(NO3)2·3H2O, pdmH2 and NaOMe in an 1:1:1 ratio, in MeOH gives the tetranuclear complex [Cu4(NO3)2(pdmH)4(H2O)(MeOH)](NO3)2 (2) in moderate yields. The cation of 2 possesses a slightly distorted tetrahedral Cu4 topology with a [Cu4(μ2-OR)4]4+ core. The pdmH− ions behave as η1:η1:η2:μ2 ligands. Strong intramolecular hydrogen bonds and π–π stacking interactions provide thermodynamic stability on compound 2. Variable-temperature, solid-state dc magnetic studies were carried out on complex 2 in the 2.0–300K range. The data indicate predominant antiferromagnetic exchange interactions and a resulting S =0 ground state, which is expected for a solely, μ2-alkoxide-bridged system with obtuse Cu–O–Cu bond angles that magnetically behaves as a Cu4 ring. A simplified 1− J model was found to be adequate to describe the variable-temperature dc susceptibility data. The data were fitted to the appropriate equation derived from the Hamiltonian H =−J 1(S 1 · S 2 + S 2 · S 4 + S 3 · S 4 + S 1 · S 3), giving the parameters J 1 =−99.5cm−1 and g =2.11(4). The combined work demonstrates the ligating flexibility of the pdmH2 chelate and its usefulness in the synthesis of oligo- and polynuclear CuII x clusters with interesting structural and magnetic properties, without requiring the co-presence of carboxylate ligands. [Copyright &y& Elsevier]

[Display omitted] We report the synthesis, magnetic EPR and conducting properties of a new manganese complex [MnII(hfac) 2 (IMHPhOPh)] 2 [MnII(hfac) 3 ](IMH 2 PhOPh) (1), containing the reduced forms (IMHPhOPh and IMH 2 PhOPh) of the NIT-PhOPh radical (NIT-PhOPh = 2,4'-benzoxo-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide). Magnetic susceptibility studies reveal the presence of weak antiferromagnetic exchange interactions between the metal ions, within the [MnII(hfac) 2 (IMHPhOPh)] 2 unit. The EPR spectra of 1 exhibit simultaneous contributions of both the monomeric [MnII(hfac) 3 ] and dimeric [MnII(hfac) 2 (IMHPhOPh)] 2 species. Conductivity measurements shown that the electrical conduction of 1 is dominated by Ohm's law, with a conductance value of 1.3 (6) × 10 - 9 S/cm. [ABSTRACT FROM AUTHOR]