As a follow-up of the studies on zinc(II) amidine complexes, solvothermal reactions involving zinc(II) sulfate heptahydrate, carboxylic acid (picolinic, pyrazinoic or quinoline-2-carboxylic acid), piperidine, nitrile (acetonitrile or propionitrile) and methanol were investigated. Two novel compounds were obtained and structurally characterized: the tetraamminezinc(II) complex [Zn(NH3)4]SO4H2O (1) and the amidinium salt (propioamH)(pipeH)SO4 (4) (propioamH+ = protonated amidine, pipeH+ = piperidinium cation). Compound 1 formed through coordination of in-situ generated ammonia, arising from the partial hydrolysis of nitrile under harsh reaction conditions, to zinc(II) ions. The double salt 4 consists of protonated propionamidine and piperidinium cations with sulfate counter-anions. The amidine is formed by the nucleophilic addition of ammonia to the triple bond of propionitrile. In addition, two previously known complexes were obtained: pipeamH[Zn(pic)3]0.5H2O (2) (pipeamH+ = protonated amidine derived from piperidine and acetonitrile, pic- = anion of picolinic acid) and [Zn(quin)2(NH3)] (3) (quin- = anionic form of quinoline-2-carboxylic acid). These results expand the understanding of zinc(II)-mediated formation of amidine species and nitrile hydrolysis.

Furosemide, a sulfonamide-based diuretic, may also be of interest as a ligand capable of binding to metal ions. Our studies of zinc-(II) coordination chemistry with furosemide in organic solvents resulted in a crystalline precipitate. Initial characterization was challenging because single crystals were of insufficient quality for an unambiguous structural determination. X-ray analysis confirmed a four-coordinate zinc-(II) complex with two deprotonated furosemides (fur-) bound in a monodentate manner and two simple monodentate ligands. Complementary techniques, i.e., infrared spectroscopy, NMR spectroscopy, and thermal analysis, revealed their identity as ammonia, generated in situ from acetonitrile hydrolysis. The composition of the product is thus [Zn-(fur)2(NH3)2]·(CH3CH2)2O (1). Although our attempt to prepare better-diffracting crystals was unsuccessful, it led to the serendipitous discovery of a new furosemide derivative, labeled 2. The derivative features two structural modifications compared to the parent furosemide, namely, ester and amidine functionalities. Single-crystal analysis of 2 showed the esterification of the carboxyl group with methanol and nucleophilic addition of the sulfonamide NH2 group to the triple bond of acetonitrile, used as a solvent. These results expand the structural chemistry of furosemide and demonstrate its capacity to undergo unprecedented transformations in zinc-(II)-mediated systems.

The coordination chemistry of copper(II) was explored using furosemide, a sulphonamide-based diuretic, as a ligand. A series of new copper(II) compounds with furosemide was synthesised and structurally characterised by single crystal X-ray diffraction. Within this series, two novel coordination modes of the deprotonated furosemide (abbreviated as fur(-)) were identified. The first one is a bidentate bridging mode (mu(2)-eta(1):eta(1)), found in dinuclear paddle-wheel (PW) complexes [Cu-2(fur)4(CH3CN)(2)]center dot 2(CH3CH2)(2)O (3) and [Cu-2(fur)(4)(CH3CH2OH)(2)]center dot 2CH(3)CH(2)OH center dot 2H(2)O (4), where carboxylate oxygens of the furosemide anion link two copper(II) centres. The second one is a unique bridging mode (mu(3)-eta(1):eta(1):eta(1)), in which the furosemide anion coordinates not only through the carboxylate oxygens but also via the sulphonamide oxygen atom, thereby linking three copper(II) ions to form a one-dimensional coordination polymer [Cu-2(fur)(4)]n center dot 4n(CH3CH2OH)center dot 2n(H2O) (5). Introduction of quinaldinate (quin(-), anion of quinoline-2-carboxylic acid) into the reaction mixture yielded the cocrystal [Cu (quin)(2)](n)center dot 2n(furH) (6), consisting of a quinaldinate-based one-dimensional coordination polymer and neutral furosemide molecules attached to the coordination polymer through hydrogen bonding. These findings provide the first structural evidence of furosemide exhibiting both bidentate and tridentate bridging behaviour, highlighting its remarkable flexibility as a ligand. Overall, this work reveals the structural diversity of resulting copper(II) complexes and broadens the understanding of ligand-metal interactions, offering new perspectives for the design of functional coordination compounds based on bioactive ligands.

The reaction systems consisting of mononuclear zinc(II) acetate dihydrate, metronidazole (met) and nitrile solvent (acetonitrile or propionitrile) have afforded heptanuclear zinc(II) compounds, [Zn7O2(CH3COO)10(met)2]center dot 2CH3CN (1) and[Zn7O2(CH3COO)10(met)2]center dot 2CH3CH2CN (2). Heptanuclear compounds 1 and 2 formed regardless of the reaction conditions: either under ambient conditions or when heated at 105 degrees C for 24 h in autoclaves. Their compositions were authenticated using single crystal X-ray crystallography. Both compounds feature the previously known {Zn7O2(CH3COO)10} structural core whose metal ions are interconnected via acetate and mu 4-oxide ligands. Two metronidazole ligands are coordinated to this core via imidazole nitrogen atoms. The zinc ions of the heptanuclear complex adopt different coordination environments: four are in nearly tetrahedral environments of four oxygen atoms, two are surrounded by NO4 donor atoms which define vertices of a distorted square pyramid and one is in an octahedral environment of six oxygen atoms. The Zn-O bonding patterns reflect both the nature and the number of donors. The solid-state structures of 1 and 2 display different intermolecular connectivities. Antibacterial testing against a series of Gram-positive and Gramnegative bacteria shows that [Zn7O2(CH3COO)10(met)2]center dot 2CH3CN (1) exhibits moderate activity against Staphylococcus epidermidis. Overall, the study advances the field of metal-based antimicrobial agents and offers new perspectives on addressing antibiotic resistance.

Zinc-(II) coordination chemistry with picolinate (abbreviated as pic-, an anion of pyridine-2-carboxylic acid) and a series of β-amino alcohols (2-aminoethanol, 2-methylaminoethanol, 2-ethylaminoethanol, 2-dimethylaminoethanol, 2-amino-1-propanol, 1-amino-2-butanol, and 1-amino-2-methyl-2-propanol) was systematically investigated. Reaction systems typically yielded complexes with the general composition [Zn-(pic)2(amino alcohol)] via a straightforward synthetic route. Zinc-(II) adopts an octahedral coordination environment consisting of two N,O-bidentate chelating picolinates and one amino alcohol, likewise coordinated in a chelating manner through amino and hydroxyl groups. As no fac isomers were isolated, the relative stability of mer and fac isomers of the 2-methylaminoethanol complex was evaluated by DFT calculations, which supported a preference for the mer geometry. Interestingly, the 1-amino-2-methyl-2-propanol system also produced an ionic species, [Zn-(pic)3]-, which crystallized as a salt with protonated amino alcohol. All novel compounds were characterized using infrared and 1H NMR spectroscopy, elemental analysis, mass spectrometry, and single-crystal X-ray diffraction. Selected tris-chelates displayed moderate antibacterial activity against S. epidermidis, with MIC values ranging from 32 to 64 μg/mL, whereas picolinic acid alone was inactive.

Reactions of (pyH)5[MoOCl4(H2O)]3Cl2 with picolinic and pyrazinoic acids yielded three new dinuclear molybdenum(V) complexes: (pyH)2[Mo2O4Cl2(pic)2]·CH3CN (1), (pyH)2[Mo2O4Cl2(pic)2]·CH3CH2CN (2) and (pyH)2[Mo2O4Cl2(pyraz)2]·CH3CN (3) (pic− = picolinate, pyraz− = pyrazinoate and pyH+ = protonated pyridine). The compounds were characterized by single-crystal X-ray diffraction, infrared and 1H NMR spectroscopy, elemental analysis, and TG/DSC measurements. All display a robust {MoV2O4}2+ core with the heteroaromatic ligands bound in a N,O-bidentate chelating manner.

Furosemide, a well-known pharmaceutical, coordinated to zinc( ii ) ions in a deprotonated form via carboxylate oxygen. Two novel complexes were obtained, a mononuclear one and a 1D-coordination polymer.

Secondary cyclic amines such as piperazine and its substituted derivatives were reacted in the presence of zinc( ii ) with acetonitrile to prepare a series of complexes. The formation of a zinc( ii ) complex with acetamidine was also investigated.

The reaction of [Zn(NH3)4]2+ in aqueous ammonia solution with quinaldinic acid (quinoline-2-carboxylic acid) gave a mononuclear heteroleptic ammine/quinaldinate complex with the [Zn(quin)2(NH3)] composition. The introduced secondary ligand adopted the usual N,O-bidentate chelating coordination. In the analogous reaction with pyrazinoic acid (pyrazine-2-carboxylic acid), complete substitution of ammonia with pyrazionate and water was observed. A mixture of two compounds formed: a mononuclear and already known [Zn(pyraz)2(H2O)2] and a novel one-dimensional (1D) coordination polymer [Zn(pyraz)2(H2O)]n. X-ray structure analysis revealed the pyrazinoate ligands in [Zn(pyraz)2(H2O)]n in two binding modes, in a bidentate chelating coordination and in a tridentate bridging coordination. The bridging pyrazinoate has engaged in binding three out of four donors: a carboxylate oxygen and both nitrogen atoms. A detailed presentation of the structure of [Zn(pyraz)2(H2O)]n and its comparison with the structures of related compounds are given below.

The influence of the zinc(II) starting material in the nucleophilic addition of piperidine (abbreviated as pipe) to acetonitrile to form amidine, piperidinoacetamidine (pipeam), was assessed. Thus, zinc(II) oxide, zinc(II) chloride or zinc(II) acetate were reacted with picolinic acid or pyrazinoic acid, piperidine and ace-tonitrile. The acid was used as a source of an N,O-donor ligand. The reactions with picolinic acid (picH) gave pipeamH[Zn(pic)3] center dot 0.5H2O ( 1 ), an amidinium salt of a homoleptic complex [Zn(pic)3]-. The same product was obtained when [Zn(pic)(picH)Cl], an already known picolinate complex, was reacted under similar conditions. The chloride-containing mixtures produced another amidine compound, (pipeamH)Cl. The reactions with pyrazinoic acid (pyrazH) gave pipeamH[Zn(pyraz)3] ( 3 ), the amidinium salt of a ho-moleptic complex [Zn(pyraz)3]-. The acetate-containing mixture yielded acetamidinium acetate. The lat-ter product indicates the presence of ammonia in the reaction. Notably, no amidine species was isolated when the coordinatively saturated pyrazinoate complex, [Zn(pyraz)2]n ( 2 ), was reacted with piperidine and acetonitrile. A detailed structural characterization of the new compounds and a discussion of their formation are presented.(c) 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ )

Three amino alcohols, 3-amino-1-propanol (abbreviated as 3a1pOH), 2-amino-1-butanol (2a1bOH), and 2-amino-2-methyl-1-propanol (2a2m1pOH), were reacted with quinoline-2-carboxylic acid, known as quinaldinic acid. This combination yielded three salts, (3a1pOHH)quin (1, 3a1pOHH+ = protonated 3-amino-1-propanol, quin− = anion of quinaldinic acid), (2a1bOHH)quin (2, 2a1bOHH+ = protonated 2-amino-1-butanol), and (2a2m1pOHH)quin (3, 2a2m1pOHH+ = protonated 2-amino-2-methyl-1-propanol). The 2-amino-1-butanol and 2-amino-2-methyl-1-propanol systems produced two polymorphs each, labeled 2a/2b and 3a/3b, respectively. The compounds were characterized by X-ray structure analysis on single-crystal. The crystal structures of all consisted of protonated amino alcohols with NH3+ moiety and quinaldinate anions with carboxylate moiety. The used amino alcohols contained one OH and one NH2 functional group, both prone to participate in hydrogen bonding. Therefore, similar connectivity patterns were expected. This proved to be true to some extent as all structures contained the NH3+∙∙∙−OOC heterosynthon. Nevertheless, different hydrogen bonding and π∙∙∙π stacking interactions were observed, leading to distinct connectivity motifs. The largest difference in hydrogen bonding occurred between polymorphs 3a and 3b, as they had only one heterosynton in common.

Copper( ii )–quinaldinate-amino alcohol reaction systems produced structurally diverse compounds with amino alcohol molecules or their deprotonated forms serving as ligands.

In the presence of zinc( ii ), propionitrile and benzonitrile react with amines to form amidines. Complexes with intact amines can also form.

The reaction systems consisting of mononuclear [(MoOCl4)-O-V(H2O)](-), carboxylate-based ligand and acetonitrile have afforded three novel polyoxomolybdate compounds. All three were characterized by X-ray structure analysis on single-crystal. The combination with phthalic acid has produced (Et3NH)(8)[(Mo4Mo12O50)-Mo-V-O-VI]center dot 2Py (Mo-16(V,VI), Et3NH+ = a protonated triethylamine, Py = pyridine), a compound with the mixed-valence hexadecanuclear cluster anion. Its four pentavalent sites form part of well-known {(Mo2O4)-O-V}(2+) units, the remaining twelve metal ions are fully-oxidized. The quinaldinate system has led to a genuine {(Mo2O4)-O-V}(2+) complex with the carboxylate ligand, (Et3NH)[(Mo2O4)-O-V(quin)(3)]center dot CH3OH (Mo-2(V), quin(-) = a deprotonated form of quinoline-2-carboxylic acid), and to a fully-oxidized compound, (PipeH)(8)[(Mo7O24)-O-VI][(MoO4)-O-VI]center dot CH3CN ((Mo7MoVI)-Mo-VI, PipeH(+) = a protonated piperidine). The latter compound contains a very rare combination of two oxomolybdate(VI) species, heptamolybdate [(Mo7O24)-O-VI](6-) and monomolybdate [(MoO4)-O-VI](2-). (C) 2021 Elsevier B.V. All rights reserved.

(PyH)2[MoOCl5] was obtained in the form of emerald green crystals unintentionally from (PyH)5[MoOCl4(H2O)]3Cl2 in acetonitrile. (PyH)2[MoOCl5] has been used as a starting material in molybdenum(V) coordination chemistry for decades, yet its true identity has not been known until now. The X-ray structure analysis has undoubtedly confirmed the existence of this compound. The [MoOCl5]2− ion displays the usual structural characteristics of the mononuclear MoO3+-containing compounds.

Trans-[Cu(quin)2(EtOH)2] (1) was synthesized as part of our study on copper(II) quinaldinate complexes with various O- and N-donor ligands. Compound 1 was characterized by infrared spectroscopy, thermal analysis and X-ray structure analysis.

Piperidine and pyrrolidine, both belonging to a group of secondary cyclic amines, reacted with acetonitrile in the presence of zinc(ii) to give the corresponding amidines that coordinated to the metal through their imine nitrogen.

The coordination of amino alcohols 3-amino-1-propanol and N-methylaminoethanol to zinc(ii) and their decomposition to ammonia were investigated.

Copper(II) acetate has reacted in methanol with quinaldinic acid (quinoline-2-carboxylic acid) to form [Cu(quin)2(CH3OH)]∙CH3OH (1) (quin− = an anionic form of the acid) with quinaldinates bound in a bidentate chelating manner. In the air, complex 1 gives off methanol and binds water. The conversion was monitored by IR spectroscopy. The aqua complex has shown a facile substitution chemistry with alicyclic secondary amines, pyrrolidine (pyro), and morpholine (morph). trans-[Cu(quin)2(pyro)2] (2) and trans-[Cu(quin)2(morph)2] (4) were obtained in good yields. The morpholine system has produced a by-product, trans-[Cu(en)2(H2O)2](morphCOO)2 (5) (morphCOO− = morphylcarbamate), a result of the copper(II) quinaldinate reaction with ethylenediamine (en), an inherent impurity in morpholine, and the amine reaction with carbon dioxide. (pyroH)[Cu(quin)2Cl] (3) forms on the recrystallization of [Cu(quin)2(pyro)2] from dichloromethane, confirming a reaction between amine and the solvent. Similarly, a homologous amine, piperidine (pipe), and dichloromethane produced (pipeH)[Cu(quin)2Cl] (11). The piperidine system has afforded both mono- and bis-amine complexes, [Cu(quin)2(pipe)] (6) and trans-[Cu(quin)2(pipe)2] (7). The latter also exists in solvated forms, [Cu(quin)2(pipe)2]∙CH3CN (8) and [Cu(quin)2(pipe)2]∙CH3CH2CN (9). Interestingly, only the piperidine system has experienced a reduction of copper(II). The involvement of amine in the reduction was undoubtedly confirmed by identification of a polycyclic piperidine compound 10, 6,13-di(piperidin-1-yl)dodecahydro-2H,6H-7,14-methanodipyrido[1,2-a:1′,2′-e][1,5]diazocine.