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Metal-organic frameworks (MOFs) are porous crystalline materials formed by coordination bonding between organic ligands and metal ions (or metal-oxo clusters). Many of them are being studied for potential application, notably, bimetallic MOFs that generally outperform their corresponding monometallic analogues [1]. Solution synthesis methods lack control over the stoichiometric ratio and the spatial arrangement of the metal centers within the framework. New synthetic strategies, such as mechanochemical synthesis, overcome these issues [2]. Here, three bimetallic MM’-MOF-74 materials, comprised of zinc (II) and copper (II) metal nodes in a 1:1 ratio, were prepared by different mechanochemical approaches and from different polymeric precursors. Synthesized materials are indistinguishable by powder X-ray diffraction (PXRD) while electron paramagnetic resonance spectroscopy (EPR) and magnetic measurements revealed the different distribution of metals in the MOFs. This was furthermore clarified by different mechanisms of framework assembly observed during in situ monitoring of reactions by synchrotron PXRD [3]. [1] L. Chen et al. Chem. Sci. 11 (2020) 5369-5403. [2] G. Ayoub et al. Chem. Mater. 31 (2019) 5494-5501. [3] S. Muratović et al. Inorg. Chem. 61 (2022) 18181-18192.

Metal-organic frameworks (MOFs) are nanoporous molecular networks with high structural and chemical diversity. MOFs show enormous potential due to the high tunability of their physicochemical properties through structural changes. Solid-state nuclear magnetic resonance (ssNMR) and electron paramagnetic resonance (EPR) spectroscopy provide information on the structure and dynamics of MOFs. They complement other spectroscopic and diffraction analyses in the search for an understanding of the relationship between structure and function in MOFs. Ball milling has been used for the stoichiometrically controlled formation of bimetallic MOF-74[1] and amorphization of MOF-74 materials.[2, 3] Here, bimetallic MOF-74 materials consisting of diamagnetic zinc (II) and paramagnetic copper (II) metal nodes in a 1:1 ratio, were prepared by different mechanochemical approaches and from different polymeric precursors. To find out their differences and how the introduction of defects and the collapse of the porous structure of MOF by mechanochemical amorphization affects their properties, we studied them by magnetic resonance spectroscopy (ssNMR and EPR). Synthesized crystalline materials are indistinguishable by powder X-ray diffraction, while ssNMR and EPR spectroscopy along with other analyses revealed different distributions of metals in the MOFs.[4] ; [1] G. Ayoub et al. Chem. Mater. 2019, 31, 5494–5501. [2] S. Muratović et al. J. Mater. Chem. C 2020, 8, 7132–7142. [3] T. Stolar et al., ACS Appl. Mater. Interfaces 2021, 13, 3070–3077. [4] S. Muratović et al. Inorg. Chem. 2022, 61 18181–18192.

A new mononuclear iron(III) octahedral complex [FeL6](BF4)3, where ligand L is 2-hydroxy-6-methylpyridine, has been synthesized and characterized by single crystal X-ray diffraction (SCXRD), magnetization measurements, electron spin/paramagnetic resonance (ESR/EPR) spectroscopy and DFT calculation.[1] The complex shows thermochromism i. e. color of the complex reversibly changes from red at room temperature to yellow-orange at the liquid nitrogen temperature. SQUID magnetization measurements reveal there is no spin-crossover of the complex ; iron(III) is in a high-spin state S = 5/2 in all temperature range 1.8295 K. The high-spin ground state of iron(III) is also confirmed by DFT calculations. X-band and multifrequency high-field/high-frequency ESR spectroscopy shows rather unusual iron(III) spectra.[2] The spectra can be simulated by temperature independent axial zero-field splitting parameter D while the value of rhombic parameter E increases on lowering the temperature. SCXRD study shows there is no temperature changes in iron(III) coordination geometry while supramolecular interactions are temperature dependent, influencing the iron(III) rhombicity. DFT calculations show temperature variation of the HOMO–LUMO gap, in agreement with the temperature changes of color and ESR spectra. References 1. K. Garg, Y. Goriya, S. Manojveer, S. Muratović, D. Pajić, M. Cetina, I. Petreska, Y. Krupskaya, V. Kataev, M. T. Johnson, O. F. Wendt and D. Žilić, Dalton Trans. 51, 2338 (2022). 2. A. Solano-Peralta, J. P. Saucedo-Vázquez, R. Escudero, H. Höpfl, H. El-Mkami, G. M. Smith and M. E. Sosa-Torres, Dalton Trans.1668 (2009).

We present the results of studying the magnetic properties of three multivariate zinc(II)/copper(II)-MOF-74 materials. Two of them, CuZn-MOF-74 and ZnCu-MOF-74, were obtained through the template-controlled mechanochemical procedure, from magnetically interesting Cu-intermediate or non-magnetic Zn-intermediate. The third one, Zn-Cu-MOF-74-alloyed, was obtained by mechanical alloying, growing MOF-74 structure from mechanically amorphized Cu-MOF-74 and Zn-MOF-74 mixture by the accelerated aging process.[1, 2, 3] While the three product materials have almost identical PXRD and FTIR spectra, they differ significantly in their magnetic properties, obtained by very detailed magnetization, X-band, multifrequency high-field ESR, and solid-state NMR measurements. The results were compared to the low-dimensional antiferromagnetic behaviour observed in both monometallic Cu-MOF-74 and Cu-intermediate, and to the magnetic properties of other similar monometallic compounds: Fe-MOF-74, Co-MOF-74, and Ni-MOF-74.

Metal-organske mreže (MOF-ovi) su kristalni, porozni materijali u kojima su metalni centri premošćujućim organskim ligandima povezani u ponavljajuće koordinacijske jedinice. MOF-74 je dobro istražena metal-organska mreža karakteristične saćaste strukture, koja joj pruža raznolika svojstva. Razvijene su brojne strategije za pripremu i modifikaciju dvometalnih MOF-ova kako bi se istražio doprinos sinergističkog efekta dvaju metala na svojstva ovih materijala [1]. Pritom se za mehanokemijsku sintezu pokazalo da osigurava dobru kontrolu nad stehiometrijskim omjerom dvaju metala u MM'-MOF-74 [2]. Naš cilj je bio proučiti kakav utjecaj izbor prekursora odnosno sintetskog pristupa ima na raspodjelu bakra i cinka u mreži, preciznije, da li je ona ravnomjerna ili postoje domene pojedinih metala. U tu svrhu mehanokemijski su pripravljeni bimetalni bakar/cink MOF-74 materijali. Iako nisu uočene strukturne razlike između sintetiziranih materijala, spektroskopija elektronske paramagnetske rezonancije (EPR) otkriva da im raspodjela metala u mreži nije jednaka. Ovo je dodatno pojašnjeno uz in situ praćenje reakcija difrakcijom sinkrotronskog rentgenskog zračenja na polikristalnom uzorku, kojim su uočeni različiti mehanizmi sklapanja mreže. [1] L. Chen, H. F. Wang, C.Li, Q. Xu Chem. Sci. 11 (2020) 5369-5403. [2]G. Ayoub, B. Karadeniz, A. J. Howarth, O. K. Farha, I. Đilović, L. S. Germann, R. E. Dinnebier, K. Užarević, T. Friščić Chem. Mater. 31 (2019) 5494-5501.

Metal-organic frameworks (MOFs) are the subject of intensive study due to their potential applications in ion exchange, drug delivery, hydrogen storage, gas separation, etc. These porous coordination polymers are comprised of metal ions/clusters that represent framework nodes and organic ligands as bonds between them. [1] M(II)-MOF-74 materials, where M(II) is a transition metal center, are widely researched for applications related to open metal sites, well-defined large channels in their honeycomb structure and also for their interesting magnetic properties arising from the complex connectivity of metal ions. Furthermore, it was shown that adsorption, stability and catalytic activity of M1(II)-MOF-74 were increased by the partial incorporation of a second metal center M2(II) in its structure, i.e. the existence of heterometal nodes.[2] We investigated magnetic properties of copper(II)-MOF-74 (Cu-MOF-74) and its three mixed analogous compounds with zinc(II). CuZn-MOF-74 and ZnCu-MOF-74 were obtained through different intermediate complexes, from magnetic Cu-INT and non-magnetic Zn-INT, respectively. The Alloyed-MOF-74 was obtained by mechanical alloying, growing the MOF-74 structure from mechanically amorphized Cu-MOF-74 and Zn-MOF-74 mixture by accelerated aging process.[3, 4] Magnetic properties of these compounds were studied by static magnetization measurements, X-band electron paramagnetic resonance (EPR) spectroscopy, multifrequency high-field high-frequency EPR (HF-EPR) spectroscopy as well as theoretical models.

Here we present the results of the study of magnetic properties of copper(II)-MOF-74 materials (Cu-MOF-74) and their three mixed analogues with zinc(II). CuZn-MOF-74 and ZnCu-MOF-74 were obtained through different intermediate complexes, namely from magnetically also interesting Cu-INT or from non-magnetic Zn-INT, respectively. The alloyed Cu-MOF-74-Zn-MOF-74 was obtained by growing the MOF structure from the mixture of milled Cu-MOF-74 and Zn-MOF-74 exposed to solvent vapors (accelerated ageing).[1] Additionally, we investigated how the amorphization process influences the magnetic properties of studied crystalline copper/zinc MOF-74 compounds.[2] Magnetic characterization was obtained by static magnetization measurements, X-band electron spin resonance (ESR) spectroscopy as well as multifrequency high-field high-frequency ESR (HF- ESR) spectroscopy. [1] G. Ayoub et al, Chem. Mater. 31 (2019) 5494. [2] S. Muratović et al, J. Mater. Chem. C 8 (2019) 7132.

The metal-organic frameworks (MOFs) are the subject of intensive research due to their promising applications in gas separation, ion exchange, sensors and catalysts.[1] However, exploring the magnetism of MOFs is a rather difficult task due to complexity of magnetic interactions.[2] Here we present a multi-frequency high-field electron spin resonance (HF-ESR) study, as well as X-band ESR and magnetization research, of magnetic properties of Ni-MOF-74 (Ni-MOF). Furthermore, we compare these results with those of a non-porous 1:1 (Ni:ligand) intermediate complex (Ni-INT) detected and isolated during the synthesis of the Ni-MOF material. Beside this, we investigate the properties of Ni-MOF when the pores or the coordination sphere of the metal sites were changed by removing the labile coordinated ligands (Ni-MOF-desolvated) and also the properties of the amorphous Ni-MOF with collapsed MOF architecture and non-existence of long-range ordering (Ni-MOF-amorph).

Metal–organic frameworks (MOFs) have attracted huge interest due to their promising properties for applications as gas-storage systems, sensors, and catalysts [1] but also because of their magnetic properties.[2] They could be defined as a class of porous polymeric materials, consisting of metal ions bridged by organic ligands. One of intensively investigated and commercially available MOF materials is MOF-74, characterized by honeycomb structure with short distances among the metal centers and open metal sites. Here we present electron spin resonance (ESR) study of magnetic properties of Ni(II)-MOF-74 (Ni-MOF) and of a non-porous intermediate complex (Ni-INT) detected and isolated during the synthesis of Ni-MOF material (Fig. 1). Also, we investigated the properties of Ni-MOF when the coordination sphere of the metal sites was changed by removing the labile coordinated ligands (Ni-MOF-empty)[3] and the properties of the amorphous Ni-MOF with collapsed MOF architecture and non-existent long-range ordering (Ni-MOF-amorph). Using the results obtained from multi-frequency (up to 321 GHz) high-field (up to 16 T) ESR (HF-ESR) as well as X-band ESR and magnetization measurements together with X-ray diffraction data, the magneto-structural correlation of the compounds will be discussed. [1] T. Yamada et al. Chem. Soc. Rev. 2013 42 6569 [2] P. Canepa et al. Phys. Rev. B 2013 87 094407 [3] A. M. Sheveleva et al. J. Phys. Chem. C 2017 121 19880 This work has been supported by Croatian Science Foundation under the projects HrZZ-UIP-2014-09-4744 and HrZZ 1108.

Reaction of 2-hydroxy-6-methylpyridine (L) with iron(II) tetrafluoroborate results in the isolation of [FeL6](BF4)3 a mononuclear iron(III) octahedral complex. X -ray diffraction studies have confirmed the existence of iron (III). Polycrystalline sample of the complex has been investigated by X-ray diffraction, magnetization and electron spin resonance (HF-ESR) spectroscopy. Beside commercially available X-band ESR, we used also multi-frequency (up to 318 GHz) high-field (up to 16 T) HF-ESR spectroscopy (Fig. 1). The obtained results will be discussed in terms of magneto-structural correlations. [1, 2] [1] P. Gamez et al. Dalton Trans. 2009, 7845-7853 [2] L. Wang et al. Chem. Eur. J. 10.1002/chem.201705989