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The crystal structure of cis-[Cr(NCS)(cyclam)(µ-NCS)ZnCl3] (cyclam = 1,4,8,11-tetraazacyclotetradecane, C10H24N4) was determined using synchrotron radiation at 100 K. The chromium(III) ion is coord...

A new complex, trans-anti/syn-[CrBr2(Me2tn)2]2ZnBr4 (1) (Me2tn = 2,2-dimethyl-1,3-propanediamine, C5H14N2), was prepared, and its structure was characterized by single-crystal X-ray diffraction and infrared (IR) spectroscopy. The complex crystallizes in the orthorhombic space group, Pnma, with eight formula units in a cell with dimensions of a = 16.415(3), b = 41.130(8), and c = 12.372(3) A. X-ray structural analysis reveals three crystallographically independent Cr(III) complex cations in the complex. In the complex cations, Cr(III) ions are coordinated by four N atoms belonging to the two chelating Me2tn and two bromides, in a trans arrangement, displaying a distorted octahedral geometry. Interestingly, the asymmetric unit contains one-half of a centrosymmetric trans-anti-[Cr1Br2(Me2tn)2]+ (2) cation, one independent trans-syn-[Cr2Br2(Me2tn)2]+ (3) cation, another half of a trans-syn-[Cr3Br2(Me2tn)2]+ (4) cation, and one ZnBr42− anion. The [Cr1Br2(Me2tn)2]+ (2) cation adopts anti chair–chair conformation, whereas the [Cr2Br2(Me2tn)2]+ (3) and [Cr3Br2(Me2tn)2]+ (4) cations adopt syn chair–chair conformations. The Cr–N(Me2tn) bond lengths vary from 2.077(4) to 2.102(5) A, and the Cr–Br bond lengths range from 2.4177(14) to 2.4933(10) A. ZnBr42− anion possesses a slightly distorted tetrahedral geometry in which the Zn–Br bond lengths and Br–Zn–Br angles are influenced by hydrogen-bonding interactions. The crystal lattice is stabilized by the hydrogen-bonding interactions between the bromides and NH groups of the Me2tn ligands.

In the title organic–inorganic salt, [CrCl2(tn)2]2[Cr2O7] (tn is propane-1,3-di­amine), the CrIII ions are coordinated by four N atoms from two tn ligands and two chloride ions in a trans geometry, displaying a distorted octa­hedral arrangement. The crystal packing is stabilized by N—H⋯Cl and N—H⋯O hydrogen bonds., The structure of the title compound, [CrCl2(tn)2]2[Cr2O7] (tn = propane-1,3-di­amine; C3H10N2), has been determined from synchrotron data. The asymmetric unit contains one CrIII complex cation and half a [Cr2O7]2− anion. In the complex cation, the CrIII ion is coordinated by the four N atoms of two propane-1,3-di­amine (tn) ligands in the equatorial plane and by two Cl atoms in a trans configuration, displaying a distorted octa­hedral coordination sphere. The two six-membered rings in the complex cation have an anti chair–chair conformation with respect to each other. The mean Cr—N(tn) and Cr—Cl bond lengths are 2.09 (1) and 2.320 (2) Å, respectively. The slightly bent dichromate anion is disordered over two sets of sites (occupancy ratio = 0.7:0.3) and has a staggered conformation. The crystal structure is stabilized by inter­molecular hydrogen bonds involving the NH2 groups of the tn ligands as donors and the O atoms of the [Cr2O7]2− anion and chlorido ligands as acceptors.

The title complex salt,trans-anti-[CrBr2(Me2tn)2]ClO4(where Me2tn = 2,2-dimethylpropane-1,3-diamine, C5H14N2), was prepared and its structure determined by single-crystal X-ray diffraction at 100 K. The asymmetric unit contains three conformationally similar complex cations and three perchlorate anions. In each complex cation, the CrIIIcentre is coordinated by four N atoms of two chelating Me2tn ligands in the equatorial plane and by two Br atoms in atrans-axial arrangement, to give a distorted octahedral geometry. Interionic contacts are dominated by extensive hydrogen bonding, involving the NH groups of the Me2tn ligand as donors and the anion O atoms or coordinated Br atoms as acceptors, resulting in two-dimensional layers in thebcplane. Ligand field analysis based on the angular overlap model, and IR and electronic spectroscopic properties, are also discussed.

The structure of trans-[Cr(2,2,3-tet)F2]ClO4 (2,2,3-tet = 1,4,7,11-tetraazaundecane) has been determined by single-crystal X-ray diffraction. The complex crystallizes in the space group P 1 ‾ of the triclinic system with two mononuclear formula units in a cell of dimensions a = 5.6741(11), b = 9.971(2), c = 13.222(3) A, α = 73.76(3)o, β = 81.08(3)° and γ = 85.12(3)°. The chromium(III) atom is in a slightly distorted octahedral environment coordinated by four N atoms of 2,2,3-tet and two F ligands in a mutually trans (meso RS) geometry. The mean Cr-N(2,2,3-tet) and Cr F bond lengths are 2.064(9) and 1.885(7) A, respectively. The crystal packing is stabilized by several hydrogen bonds. The 5 K sharp-line absorption spectrum and the 298 K FT-infrared and UV–visible spectra have been measured. Using the electronic transitions, a ligand field optimization has been performed to determine the metal-ligand bonding properties of the coordinated atoms. It is found that the fluoride is a strong σ- and π-donor and the nitrogen atoms of the 2,2,3-tet ligand also have strong σ-donor properties toward the chromium(III).

The CrIII ion in the title complex is coordinated by two 1,10-phenanthroline (phen) ligands, one water mol­ecule and a chloride in a cis geometry, displaying a distorted octa­hedral environment. The [ZnCl4]2− anion has a slightly distorted tetra­hedral coordination geometry., The structure of the title compound, [CrCl(C12H8N2)2(H2O)][ZnCl4]·H2O, has been determined from synchrotron data. The CrIII ion is bonded to four N atoms from two 1,10-phenanthroline (phen) ligands, one water mol­ecule and a Cl atom in a cis arrangement, displaying an overall distorted octa­hedral coordination environment. The Cr—N(phen) bond lengths are in the range of 2.0495 (18) to 2.0831 (18) Å, while the Cr—Cl and Cr—(OH2) bond lengths are 2.2734 (7) and 1.9986 (17) Å, respectively. The tetra­hedral [ZnCl4]2− anion is slightly distorted owing to its involvement in O—H⋯Cl hydrogen bonding with coordinating and non-coordinating water mol­ecules. The two types of water mol­ecules also inter­act through O—H⋯O hydrogen bonds. The observed hydrogen-bonding pattern leads to the formation of a three-dimensional network structure.

In the title compound, [CrCl2(C7H20N4)]ClO4, the CrIII ion is coordinated by four N atoms from the 1,4,8,11-tetra­aza­undecane ligand and two chloride ions in a trans geometry, displaying a distorted octa­hedral arrangement. The crystal packing is stabilized by N—HCl and N—H⋯O hydrogen bonds., The structure of the title complex, [CrCl2(2,3,2-tet)]ClO4 (2,3,2-tet is 1,4,8,11-tetra­aza­undecane, C7H20N4), has been determined from synchrotron data. The CrIII ion is coordinated by the four N atoms of the 1,4,8,11-tetra­aza­undecane ligand in the equatorial plane and two chloride ions in an axial arrangement, displaying a slightly distorted octa­hedral coordination environment. The two H atoms of the secondary amines are grouped on the same side of the equatorial N4 plane (meso-RS conformation). The Cr—N bond lengths range from 2.069 (2) to 2.084 (2) Å, while the mean Cr—Cl bond length is 2.325 (2) Å. The crystal structure is stabilized by inter­molecular hydrogen-bonding inter­actions between the primary and secondary amine groups of the 2,3,2-tet ligands, the Cl ligands and the O atoms of the perchlorate counter-anion, forming corrugated layers parallel to (010).

The structure of trans-[Cr(tn)2Br2]ClO4 (tn = propane-1, 3-diamine) has been determined by a single-crystal X-ray diffraction study at 100 K. The complex crystallizes in the space group P of the triclinic system with two mononuclear formula units in a cell of dimensions a = 6.8220(4), b = 8.86199(9), c = 12.6644(8) A and α = 77.859(7)°, β = 81.765(6)°, and γ = 77.764(7)°. The chromium atom is in a slightly distorted octahedral environment coordinated by four nitrogen atoms of two tn ligands and two bromine atoms in trans positions. The two six-membered chelate rings in the complex cations are oriented in an anti chair-chair conformation with respect to each other. The mean Cr–N(tn) and Cr–Br bonds are 2.093(3) and 2.4681(4) A, respectively. The crystal packing is stabilized by hydrogen bonds. The infrared and electronic absorption spectral properties are consistent with the result of X-ray crystallography. It is confirmed that the nitrogen atoms of the tn ligand are strong σ-donors, but the bromido ligands have weak σ- and π-donor properties toward the chromium(III) ion.

The complex [Cr(cyclam)(acac)](ClO(4))(2)center dot 0.5H2O (cyclam = 1,4,8,11-tetraazacyclotetradecane; acac = acetylacetonate) was prepared and structurally characterized by single-crystal X-ray diffraction at 100 K. The chromium atom is in a slightly distorted octahedral environment with four nitrogen atoms of the macrocyclic ligand and two O-bonded acac molecules in cis position. The cyclam ligand adopts the folded cis-V configuration with six- and five-membered chelate rings in chair and gauche conformation, respectively. The average CrN(cyclam) and CrO(acac) bonds are 2.080(4) and 1.941(3) angstrom, respectively. The IR and visible spectral properties are also described.

The structure of trans-[Cr(Me2tn)2Cl2]2ZnCl4 (Me2tn = 2,2-dimethylpropane-1,3-diamine) was determined by a single-crystal X-ray diffraction study at 173 K. The analysis reveals that there are three crystallographically independent chromium(III) complex cations in the title compound. The chromium(III) atoms are coordinated by four nitrogen atoms of Me2tn and two chlorine atoms in a trans arrangement, displaying a distorted octahedral geometry. The two six-membered chelate rings in three complex cations are oriented in an anti chair–chair conformation with respect to each other. The Cr–N and Cr–Cl bond lengths average 2.0862(2) and 2.3112(6) A, respectively. The ZnCl42– have slightly distorted tetrahedral arrangement with Zn–Cl lengths and the Cl–Zn–Cl angles are influenced by hydrogen bonding. The resolved absorption maxima in the electronic d–d spectrum were fitted with a secular determinant for a quartet energy state of the d3 configuration in a tetragonal field. It is confirmed that the nitrogen atoms of the Me2tn ligand are strong σ donors, but the chloro ligands have weak σ- and π donor properties toward the chromium(III) ion.

The new complex, cis-β-[Cr(2,2,3-tet)(N3)2]Br (2,2,3-tet = 1,4,7,11-tetraazaundecane), was prepared and its structure was determined by single-crystal X-ray diffraction. The chromium(III) atom is in a distorted octahedral environment coordinated by four nitrogen atoms of 2,2,3-tet and two azido ligands in a cis-β arrangement, with bent Cr–N3 linkages at the coordinating azide nitrogen atoms. The mean Cr–N(2,2,3-tet) and Cr–N(azide) bond lengths are 2.084(5) and 2.021(5) A, respectively. The crystal structure is stabilized by ionic interactions, supported by N–H···N(azide) and N–H···Br hydrogen bonds. The IR and electronic spectroscopic properties are also discussed.

The novel complex trans -[Cr(Me 2 tn) 2 (NCS) 2 ]NCS·1/2H 2 O, where Me 2 tn represents 2,2-dimethylpropane-1,3-diamine, was prepared and its structure was determined by single-crystal X-ray diffraction at 150 K. The complex crystallizes in the space group P 1 ¯ of the triclinic system with two mononuclear formula units in a cell of dimensions a = 8.8359(6), b = 10.4926(7), c = 12.5136(9) A and α = 66.124(2)° , β = 88.795(2)° and γ = 89.530(2)°. The chromium atom is in a slightly distorted octahedral environment coordinated by four N atoms of two chelating Me 2 tn and two N-bonded thiocyanate ligands in trans axial positions. The two six-membered rings in the complex cation have only anti chair–chair conformations with respect to each other. The mean Cr–N(Me 2 tn) and Cr–N(CS) bonds are 2.0807(15) and 1.9826(15) A, respectively. The crystal structure is stabilized by N–H…S and N–H…N hydrogen bonds. The ligand field analysis as well as the IR and electronic spectral properties are discussed.

The2,3,2-tet ligand is a structural isomer of 1,4,7,11-tetra-azaundecane (2,2,3-tet). The linear tetradentate with fournitrogen atoms as donors can adopt three different configu-rations in chromium(III) complexes with two chloro ligandsas shown in Figure 1. Generally, the chromium(III) tetra-dentate complexes have been shown to have a diversestereochemistry. It is not possible from the CD spectrum toassign the

The structure of [CrF(2)([15]aneN(4))]ClO(4).H(2)O ([15]aneN(4)=1,4,8,12-tetraazacyclopentadecane) has been determined by a single-crystal X-ray diffraction study at 173 K. The complex crystallizes in the space group P1- of the triclinic system with two mononuclear formula units in a cell of dimensions a=9.6117(7) A, b=10.2882(7) A, c=11.0001(7) A and alpha=99.7570(10) degrees, beta=105.6080(10) degrees and gamma=113.7130(10) degrees. The complex cation unit has its central Cr atom in an octahedral coordination with four nitrogen atoms and two fluorine atoms in a trans position. Three six-membered and one five-membered chelate rings of the [15]aneN(4) ligand are in a chair-twist(skew)-chair-gauche conformation sequence. The gauche five-membered ring is disordered with the twist six-membered ring opposite. The four H atoms in the chiral N atoms have the trans-II (CTCg) type configuration. The mean Cr-N and Cr-F bonds are 2.095(2) and 1.8752(13) A, respectively. The IR and visible spectral properties are consistent with the result of X-ray crystallography. The resolved band maxima of the electronic d-d spectrum are fitted with secular determinant for quartet state energy of d(3) configuration in tetragonal field including configurational but neglecting spin-orbit coupling. It is confirmed that the fluoride has strong sigma- and pi-donor properties toward the chromium(III) ion and the nitrogen atoms of the [15]aneN(4) ligand also have a strong sigma-donor character.

The sharp-line absorption and emission spectra of(H 1 3 O 6 ){trans-[Cr(Me 2 tn) 2 Br 2 ]} 2 Br 2 (Cl0 4 ) (Me 2 tn = 2,2-dimethyl-l,3-diaminopropane) have been measured between 13000 cm - 1 and 16000 cm - 1 at 5 K. The 298 K infrared and visible absorption spectra have also been measured. The nine electronic bands due to spin-allowed and spin-forbidden transitions were assigned. Using observed transitions, a ligand field analysis has been performed to probe the ligand field properties of coordinated atoms in the title chromium(III) complex ion. The zero-phonon line in the sharp-line absorption spectrum splits into two components by 286 cm - 1 , and the large ""Eg splitting can be reproduced by the modern ligand field theory. It is confirmed that nitrogen atoms of the Me 2 tn ligand have a strong cr-donor character, but the bromide has weak σ- and π-donor properties toward chromium(III) ion.

The absorption spectra of microcrystalline salts of cis -[Cr(cyc b )(O 2 CO)] + (cyc b = rac -5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) have been measured between 13,000 and 50,000 cm −1 at temperatures down to 2 K. The vibrational intervals of the electronic ground state were extracted by recording emission and far-IR spectra. The zero-phonon line in the sharp-line absorption spectrum splits into two components by 144 cm −1 . The nine electronic bands due to spin-allowed and spin-forbidden transitions were assigned. Using the observed transitions, a ligand-field analysis has been performed to probe the ligand-field properties of carbonato group in the chromium(III) complex. It is found that the carbonato oxygen has moderately strong σ- and π-donor properties toward chromium(III) ion.

The electronic absorption spectra of trans-[CrX 2 ([15]aneN 4 )]ClO 4 ([15]aneN 4 =1,4,8,12-tetraazacyclo-pentadecane; X=F, Cl) complexes have been interpreted using the ligand field theory. An AOMX program is used to opti-mize the differences between the calculated and the observed positions for the spin-allowed transition bands. The crystalfield theory(CFT) parameter is directly related to the angular overlap model(AOM), normalized spherical harmonichamiltonians(NSH), and semiempirical parameters. The various ligand field parameters are discussed in terms of theirchemical significances. According to the ligand field analysis, we can confirm that the fluoride ligand is a very strongσ- and π-donor while the chloride has weak σ- and π-donor properties toward chromium(III) ion.Keywords:Cr(III) Complex, Electronic Transition, Ligand Field Analysis, [15]aneN 4 `@ 2_ ( ' ab LM E c 3 + d'< :; 89 de fN ? D j ghi lm kn" .

We report here the low temperature emission spectra in the heterometal dinuclear 3d–4f assembled molecular system [(acac) 2 Cr III (μ-ox)Ln III (HBpz 3 ) 2 ] (Cr(ox)Ln:acac − =acetylacetonate, ox 2− =oxalate, HBpz 3 − =hydrotris(pyrazol-1-yl)borate; Ln=La, Nd, Ho, Er , Tm and Yb) in comparison with those of Na[Cr(acac) 2 (ox)] and [(HBpz 3 ) 2 Ln(μ-ox)Ln(HBpz 3 ) 2 ](Ln=Nd and Er). From 10 to 150 K the Cr(ox)Ln complexes show a broad emission band around 800 nm from the 2 E state of Cr(III) moiety. At room temperature no 2 E– 4 A 2 emission was observed in the Cr(ox)Ln except for the La and Lu complexes. On warming from 10 to 300 K rapid quenching of the 2 E– 4 A 2 emission of Cr(III) is suggested to result from the energy transfer from Cr to Ln in the Cr(ox)Ln. The excitation spectra and the life-time were also measured with monitoring the 4f–4f emission peaks of the Cr(ox)Yb complex.

The crystal structure of the title compound, (C(2)H(10)N(2))[Cr(C(4)H(9)N(2)O(2))(2)](2)Cl(4) x 2H(2)O, has been determined by single-crystal X-ray diffraction studies at 293 and 100 K. The analyses demonstrated that the crystal consists of ethylenediammonium dications (which lie about inversion centres), bis[N-(2-aminoethyl)glycinato]chromium(III) monocations, Cl(-) anions and hydrate water molecules, in a molecular ratio of 1:2:4:2. The complex cation unit has a slightly distorted octahedrally coordinated Cr atom, with two Cr[bond]O and four Cr[bond]N bonds in the ranges 1.951 (1)-1.953 (1) and 2.054 (1)-2.089 (2) A, respectively, at 293 K. The geometry of the bis[N-(2-aminoethyl)glycinato]chromium(III) moiety was found to be trans,cis,cis with respect to the carboxylate O atom and the primary and secondary amine N atoms. The two analyses, at 293 and 100 K, exhibited no remarkable structural differences, although the colour of the crystals did differ, being red at 293 K and orange at 100 K.

The mixed ligand complex [Cr( l -progly)(dpt)]ClO 4 [H 2 progly=prolylglycine, dpt=di(3-aminopropyl)amine] has been prepared, and its geometric structure was discussed on the basis of electronic absorption and IR spectral data. The emission and excitation spectra taken at 77 K were also reported. The 12 electronic bands due to spin-allowed and spin-forbidden transitions were assigned. Using the electronic transitions, a ligand-field optimization has been performed to determine the metal–ligand bonding properties for the coordinated atoms. We confirmed that the peptide nitrogen of prolylglycinate has moderate strong σ- and weak π-donor properties toward chromium(III) ion.

The preparation and characterization of novel chromium(III) complexes have received much attention because the chromium(III) materials are promising materials for tunable solid state laser in the spectral region between 600 and 1100 nm. 1 As a prerequisite for these applications, a detailed study of the spectroscopic and ligand field properties is needed. Furthermore, the geometrical and conformational isomerism in transition metal complexes has been an area of intense activity and has provided much basic structural information. 2 The 2,2-dimethylpropane-1,3-diamine (Me2tn) as a bidentate ligand can coordinate to a central metal ion forming a six-membered ring, and the spectroscopic properties of the resulting metal complexes can be compared with those of the corresponding complexes containing the unsubstituted tn diamine system. 3

The title salt, Na[CrF2(C5H5N)4]2[ZnCl4]ClO4, consists of two cationic CrIIIcomplexes, an Na+cation, one [ZnCl4]2−anion and one ClO4−anion. The CrIIIatoms are coordinated by four pyridine (py) N atoms and two F atoms in atransarrangement, displaying a distorted octahedral geometry. The mean Cr—N(py) and Cr—F bond lengths are 2.086 (8) and 1.864 (14) Å, respectively. The [ZnCl4]2−anion has a distorted tetrahedral geometry. The most notable feature of the crystal packing is the formation of weak pyridine–perchlorate C—H...O hydrogen bonds, resulting in supramolecular chains along theb-axis direction. The perchlorate anion was disordered over two sets of sites in a 0.868 (3):0.132 (3) ratio.

The 77 K emission and excitation spectra, and 298 K infrared and absorption spectra of cis -[Cr(cyclam)(ONO) 2 ]NO 3 (cyclam=1,4,8,11-tetraazacyclotetradecane) have been measured. The vibrational intervals of the electronic ground state are extracted from the far-infrared and emission spectra. The 10 electronic bands due to spin-allowed and spin-forbidden transitions are assigned. Using the observed electronic transitions, a ligand field analysis was performed in the framework of the angular overlap model. It is confirmed that nitrogen atoms of the cyclam ligand have a strong σ-donor character, but nitrito ligand has weak σ- and π-donor properties toward chromium(III) ion.

The crystal structure of [Cr(NCS)2(cyclam)]NCS (cyclam = 1,4,8,11-tetra-aza-cyclo-tetra-deca-ne, C10H24N4) has been determined by using synchrotron radiation at 98 K. The Cr(III) atom is in a slightly distorted octa-hedral environment with four N atoms of the macrocyclic ligand and two N-coordinated NCS(-) anions in cis positions. The average Cr-N(cyclam) and Cr-NCS bond lengths are 2.085 (5) and 1.996 (15) Å, respectively. In the crystal, the uncoordinating SCN(-) anion is hydrogen bonded through N-H⋯S and N-H⋯N inter-actions to neighbouring complex cations.

In the title compound, [Cr(ONO)(2)(cyclam)]NO(2) (cyclam is 1,4,8,11-tetraazacyclotetradecane, C(10)H(24)N(2)), the complex cation is located on a twofold symmetry axis. The central Cr atom has a distorted octahedral coordination, involving two Cr-O bonds, with the monodentate nitrite O atoms adopting a cis configuration, and four Cr-N bonds. The mean Cr-N and Cr-O distances are 2.0895 (14) and 1.9698 (14) A.

The crystal structure of [Cr(edda)(acac)] (edda = ethylediamine-N,N'-diacetate; acac = acetylacetonato) has been determined by a single crystal X-ray diffraction study at 150 K. The chromium ion is in a distorted octahedral environment coordinated by two N and two O atoms of chelating edda and two O atoms of acac, resulting in s-cis configuration. The complex crystallizes in the space group P2(1)/c of the monoclinic system in a cell of dimensions a = 10.2588(9), b = 15.801(3), c = 8.7015(11) A, β =101.201(9)° and Z = 4. The mean Cr-N(edda), Cr-O(edda) and Cr-O(acac) bond distances are 2.0829(14), 1.9678(11) and 1.9477(11) A while the angles O-Cr-O of edda and O-Cr-O of acac are 171.47(5) and 92.72(5)°, respectively. The crystal structure is stabilized by N-H···O hydrogen bonds linking [Cr(edda)(acac)] molecules in distinct linear strands. The visible electronic and IR spectroscopic properties are also discussed. An improved, physically more realistic force field, Vibrationally Optimized Force Field (VOFF), capable of reproducing structural and vibrational properties of [Cr(edda)(acac)] was developed and its transferability demonstrated on selected chromium(III) complexes with similar ligands.

An Angular Overlap Model calculation was used to fit the electronic spectrum, particularly the sharp-line positions, of [Cr(dpt)(glygly)]ClO 4 ·0.5C 4 H 6 N 2 O 2 ·2.5H 2 O [dpt = di(3-aminopropyl)amine, H 2 glygly = glycylglycine] at 77 K. An e π value of 502 cm −1 for the peptide nitrogen indicates that it is a weak net π-donor to chromium(III), presumably because donation from the filled π-orbital and back-donation to the empty π-antibonding orbital are almost in balance.

The structure of trans-[CrCl(2)(Me(2)tn)(2)]Cl (Me(2)tn=2,2-dimethylpropane-1,3-diamine) has been determined by a single-crystal X-ray diffraction study at 150K. The analysis reveals that there are two independent Cr(III) complex cations in the structure, one with crystallographic inversion symmetry and the other with two-fold rotation symmetry, which are conformational isomers of each other. In both conformations, the chromium atom adopts a distorted octahedral structure with the four nitrogen atoms of two Me(2)tn ligands occupying the equatorial plane and two chlorine atoms occupying trans-axial positions. The six-membered chelate rings are in stable chair conformations with N-Cr-N angles of 87.03(8) degrees and 88.99(8) degrees . The two chelate rings in the centrosymmetric complex cation 1 are anti, while those in the rotation-symmetric complex cation 2 are in syn conformations. The mean Cr-N and Cr-Cl bond lengths are 2.0922 and 2.3253 A, respectively. The infrared and UV-visible absorption spectra of trans-[CrCl(2)(Me(2)tn)(2)]Cl have also been measured. The resolved band maxima of the electronic d-d spectrum are fitted with a secular determinant for a quartet energy state of the d(3) configuration in a tetragonal field including configurational but neglecting spin-orbit coupling. It is confirmed that the nitrogen atoms of the Me(2)tn ligand have a strong sigma-donor character, but the chloro ligand has weak sigma- and pi-donor properties toward the chromium(III) ion.

The emission and excitation spectra of cis-[Cr(cyclam)(N3)2](N3) (cyclam=1,4,8,11-tetraazacyclotetradecane) taken at 77 K are reported. The infrared and visible spectra at room temperature are also measured. The vibrational intervals due to the electronic ground state are extracted from the far-infrared and emission spectra. The ten electronic bands due to spin-allowed and spin-forbidden transitions are assigned. Using the observed transitions, a ligand field analysis has been performed to determine the bonding property of azido group in the chromium(III) complex. It is found that azide ligand has weak σ- and π-donor properties toward chromium(III) ion. The zero-phonon line in the excitation spectrum splits into two components by 249 cm−1, and the large 2Eg splitting can be reproduced by the ligand field theory.

The crystal structure of the title compound, K2[Cr2(C6H6NO6)2(OH)2]·6H2O or K2[Cr2(μ-OH)2(nta)2]·6H2O (nta = nitrilo­tri­acetate), is composed of a dinuclear hydro­xo-bridged chromium(III) complex anion, potassium cation and water mol­ecules. Each CrIII ion is in a distorted octahedral environment and coordinated by one nitro­gen and three carboxyl­ate O atoms of the nta3− ligand plus two bridging hydro­xo O atoms. The dinuclear complex anion possesses 2/m crystallographic symmetry. The Cr—O(μ-OH) bond lengths are 1.937 (4) and 1.951 (4) A. The Cr—N and Cr—O bond distances of the nta3− ligand are 2.054 (4) and 1.968 (3)–1.983 (3) A, while the HO—Cr—OH and Cr—OH—Cr angles are 80.46 (16) and 99.54 (16)°, respectively.

In the title compound, [CrCl2(C3H10N2)2]2[ZnCl4], the CrIII atom is coordinated by four N atoms of propane-1,3-diamine (tn) and two Cl atoms in a trans arrangement, displaying a distorted octahedral geometry with crystallographic inversion symmetry; the Zn atom in the [ZnCl4]2− anion lies on a -4 axis. The orientations of the two six-membered chelate rings in the complex cation are in an anti chair–chair conformation with respect to each other. The Cr—N bond lengths are 2.087 (6) and 2.097 (6) Å. The Cr—Cl and Zn—Cl bond lengths are 2.3151 (16) and 2.3255 (13) Å, respectively. Weak intermolecular hydrogen bonds involving the tn NH2 groups as donors and chloride ligands of the anion and cation as acceptors are observed.

In the title compound, [CrCl2(C3H10N2)2]ClO4, the CrIII atom is coordinated equatorially by four N atoms of two propane-1,3-diamine (tn) ligands and axially by two mutually trans Cl atoms, thus displaying a slightly distorted octa­hedral geometry with no crystallographically imposed symmetry. The two six-membered chair chelate rings in the complex cation are in an anti conformation with respect to each other. The Cr—N bond lengths range from 2.0831 (18) to 2.0917 (19) A, and the Cr—Cl bond lengths are 2.3148 (6) and 2.3135 (6) A. The perchlorate anions have slightly distorted tetra­hedral geometries. Weak inter­molecular hydrogen bonds involving the tn ligand NH groups as donors, and chloride ligands and anion O atoms as acceptors are observed.

In the title salt, [CrCl(2)(C(5)H(14)N(2))(2)]ClO(4), the Cr atom is in a trans-CrCl(2)N(4) octa-hedral environment comprising the four N atoms of two chelating 2,2-dimethyl-propane-1,3-diamine ligands and two Cl atoms. The two six-membered CrC(3)N(2) rings in the cation adopt anti chair-chair conformations with respect to each other. The perchlorate anion is disordered over two positions in respect of the Cl and an O atom in a 6:4 ratio. N-H⋯O hydrogen bonds link the cations and anions into a layer structure.