Preparation and structure of 1RS,4SR,7SR,10RS- (1,4,7,10-tetraazacyclopentadecane)copper(II) tetrachlorozincate

Abstract

The structure of 1RS,4SR,7SR,10RS-(1,4,7,10-tetraazacyclopentadecane)copper(II) tetrachlorozincate, determined at 120 K, is reported: C₁₁H₂₆Cl₄CuN₄Zn, orthorhombic, P b c a (Hall−P 2ac 2ab); a, 14.0675(7); b, 14.4206(6); c, 18.2106(10) Å. The cation has approximate two-fold symmetry, with the CuN₄ group tetrahedrally twisted, with NH groups alternating on opposite sides of the N₄ group around the ring. The five-membered chelate rings have gauche conformations and the eight-membered chelate ring has an extended twist conformation. The anion and cation are linked into chains by hydrogen bonds and weak Cu···Cl interactions.

Keywords:

• Crystal structure
• Copper(II) compound
• 1,4,7,10-Tetraazacyclopentadecane
• Cyclic tetraamine
• Chelate rings

Introduction

The preparation, studies of formation constants, spectra, reaction kinetics and structural modeling of metal-ion compounds of the cyclic tetraamine 1,4,7,10-tetraazacyclopentadecane, tcp, have been described [1–14], but structures of few compounds have been reported. The structures of the compounds of tcp are of interest because of the presence of the very flexible eight-membered chelate ring, which can adopt a variety of conformations. Salts of trans-[Co(tcp)Cl₂]⁺ occur as green or brown crystals. The structures of green NO ₃⁻ (1) and BF ₄⁻ salts (2 and 3) and brown salts (ambient temperature, 4 and 113 K, 5) were determined [12]. These all have the same 1RS,4SR,7SR,10RS configuration, with NH groups alternating on opposite sides of the N₄ group around the ring (cyclam configuration V). The conformation of the eight-membered chelate ring is described as boat–boat for the NO ₃⁻ salt (1) and for a monoclinic modification of the BF ₄⁻ salt (2), disordered boat–boat (40%), boat–boat–chair (60%) for an orthorhombic modification of the BF ₄⁻ salt (3) and for the salt (4) at ambient temperature and as twist–boat–chair for the salt at 113 K (5). In contrast, square-planar coordinated [Ni(tcp)](ClO₄)₂ has the 1RS,4SR,8RS,11SR configuration (cyclam configuration III), with very approximate mirror symmetry, with the eight-membered ring in an extended boat-like conformation with conformational disorder, with the two NH groups and all atoms of this chelate ring on the same side of the CuN₄ group [5]. Other compounds with saturated eight-membered chelate rings which have been structurally characterized include cis-di-isothiocyanato-(1,5,9-triazacyclotetradecane)-nickel(II) monohydrate and -cobalt(II) [15] which have the eight-membered chelate ring in boat-like conformations. Compounds of Co(II), Ni(II) and Cu(II) with the 17-membered tetraazamacrocycle (6,7,8,9,10,11,12,13,18,19,20,21- dodecahydro-5H-dibenzo(e,p)(1,4,8,12)-tetraazacyclo heptadecine) have eight-membered chelate rings in twist conformations [16] and a compound of this macrocycle with cadmium(II) has this chelate ring which has a boat-like conformation, with disorder [17]. Compounds of technetium with 3,3,11,11-tetramethyl-4,10-diazatridecane-2,12-dione dioxime have an eight-membered chelate ring in a boat-like conformation [18,19].

Results

We now report the preparation and structure of [Cu(tcp)][ZnCl₄]. This deep blue compound has a structure in which the macrocycle is in square-planar coordination to Cu(II), with the configuration 1RS,4SR,7SR,10RS, with NH groups alternating on opposite sides of the N₄ “plane” around the ring, the same as found for Co(III) compounds of tcp [5]. The asymmetrical unit is shown in Figure 1, and selected dimensions in Table 1.

Figure 1. The asymmetrical unit of [Cu(tcp)][ZnCl₄], drawn [24] with displacement ellipsoids at 50% probability and with hydrogen atoms shown as circles of arbitrary radius.

Table 1.  Selected dimensions for [Cu(tcp)][ZnCl₄].

Atoms	Distance (Å)	Atoms	Angle (°)
Cu1‒N1	2.045(3)	N1‒Cu1‒N4	84.9(2)
Cu1‒N4	2.005(3)	N1‒Cu1‒N7	167.4(2)
Cu1‒N7	1.993(3)	N1‒Cu1‒N10	107.2(2)
Cu1‒N10	2.044(3)	N4‒Cu1‒N7	83.9(2)
Cu1···Cl1	3.091(1)	N4‒Cu1‒N10	167.0(2)
Cu1···Cl2^a	3.029(1)	N7‒Cu1‒N10	84.5(2)
		Cl1···Cu1···Cl2^a	169.38(3)
		Cu1···Cl1‒Zn1	125.00(3)
		Cu1···Cl2^a‒Zn1^a	118.17(3)

^aSymmetry operation:

The cation has approximate two-fold symmetry about an axis from the mid-point of the C5–C6 bond, through Cu1 to C13. In contrast, [Ni(tcp)](ClO₄)₂ has the 1RS,4SR,8RS,11SR configuration with very approximate mirror symmetry, through these positions [5]. The N₄ group of [Cu(tcp)]²⁺ is tetrahedrally twisted, with Cu1 in the N₄ plane. Displacements (Å) of atoms from the N1,N4,N7,N10 best plane are: N1, −0.082(2); N4, 0.101(2); N7, −0.102(2); N10, 0.083(2); Cu1, −0.001(2). The three five-membered chelate rings have gauche conformations, with displacements (Å) of atoms from the CuN₂ planes of: plane Cu1,N1,N4: C2, 0.024(7); C3, −0.667(7); plane Cu1,N4,N7: C5, −0.382(6); C6, 0.369(6); plane Cu1,N7,N10: C8, 0.675(6); C9, −0.009(6). The eight-membered chelate ring has an extended twist conformation, similar to those of the structures (1) and (2) for the cobalt compounds, above, with displacements (Å) from the plane Cu1,N1,N10: C11, −0.883(7); C12, −1.306(8); C13, −0.258(9); C14, 1.038(8); C15, 0.963(7).

The [Cu(tcp)]²⁺ cations and the [ZnCl₄]²⁻ anions are linked into chains ‒Cl‒Zn‒Cl···Cu···Cl‒Zn (Figure 2). The long Cu···Cl distances (Table 1) indicate that this coordination interaction is very weak and the structure is determined primarily by N‒H···Cl hydrogen bonds of Cl1 with N1 and N7 and of Cl2 with N4 and N10. These chains are cross-linked by further N˭H···Cl hydrogen bonds (Table 2). The most similar structure of this type in the Cambridge Crystallographic Data Centre (CCDC) is of [Cu(L)][CuBr₃], where L=1,4,8,12-tcp [20]. The long Cu···Cl distances can be compared with those for (4,6,6-trimethyl-3,7-diazanon-3-ene-1,9-diamine)copper(II) tetrachlorozincate of 2.680 Å [21] and (2,4-dimethyl-5,8-diazadec-4-ene-2,10-diamine)copper(ii) tetrachlorozincate of 2.6630(7) Å [22] for which the chloride is more definitively coordinated axially.

Figure 2. [Cu(tcp)][ZnCl₄] drawn as for Figure 1, showing the chain structure, with hydrogen atoms omitted for clarity. Symmetry operation for atoms marked i=x,−y+1/2, z+1/2.

Table 2.  Hydrogen bonds (Å,°) for [Cu(tcp)][ZnCl₄].

N‒H···Cl	N‒H	H···Cl	N···Cl	N‒H···Cl	Symm. operation
N1‒H1···Cl1	0.91(5)	2.64(4)	3.379(3)	138(4)
N4‒H4···Cl4	0.91(5)	2.49(5)	3.226(3)	138(4)
N4‒H4···Cl2	0.91(5)	2.74(4)	3.349(3)	125(3)
N7‒H7···Cl3	0.80(5)	2.50(5)	3.228(4)	152(4)
N7‒H7···Cl1	0.80(5)	2.96(5)	3.458(3)	122(4)
N10‒H10···Cl4	0.78(5)	2.54(5)	3.261(3)	155(4)

For the [ZnCl₄]²⁻ anion, the Zn‒Cl distances range from 2.261(1) Å for Zn1‒Cl3 to 2.311(1) Å for Zn1-Cl1 and the Cl‒Zn‒Cl angles from 104.01(1)° for Cl2‒Zn1‒Cl4 to 116.10(4)° for Cl1‒Zn1‒Cl2.

Experimental

Preparation

The tcp was prepared as previously reported [1–5]. [Cu(tcp)][ZnCl₄] was prepared by reacting equimolar amounts of tcp, CuClO and ZnCl₂ in ethanol. The deep blue product was filtered off and recrystallized by evaporation of an aqueous solution.

Structure determination

1RS,4SR,7SR,10RS-(1,4,7,10-Tcp)copper(II) tetrachloro zincate, C₁₁H₂₆Cl₂CuN₄Zn, M_r 499.09, orthorhombic, P b c a (Hall −P 2ac 2ab); a, 14.0675(7); b, 14.4206(6); c, 18.2106(10) Å; ; V, 3694.2(3) Å³; Z, 8; T, 120.0(1) K; cell measurement from 6291 reflns., . Dark blue block grown from water,  mm³; μ, 8.319 mm⁻¹; , 1.744 g cm⁻³; F000, 1976. Multi-scan absorption correction, T_min, 0.191; T_max 1.000 (empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm, CrysAlisPro, Agilent Technologies). Diffraction data were collected at 120(1) K by using a SuperNova (Cu) X-ray Source with a mirror monochromator (λ 1.5418 Å) and a SuperNova, Dual, Cu at zero, Atlas Diffractometer (area resol. mean = 5.3250). Refl. number 13264 (avge. ); ; . 2843 Indep. refl., 2843 refl. with . Data collection and processing used CrysAlisPro, Agilent Technologies (version 1.171.36.28). The structure solved and refined using SHELXTL [20], with H(C) in calculated positions, refined with a riding model with SHELX defaults; 202 parameters, 0 restraints. Data , R₁=0.0379; ; all data, R₁=0.0456; ; g.o.f., 1.048.

Supplementary material

Supplementary crystallographic data for [Cu(tcp)]ZnCl₄, CCDC 950137, can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: [phone]; or e-mail: [email protected].