Structural diversity and variable temperature magnetic properties in copper dimethylmalonate coordination polymers containing dipyridyl-type coligands

Article abstract of DOI:10.1016/j.poly.2019.06.018

Four copper dimethylmalonate (dmmal) phases containing long-spanning dipyridyl coligands have been prepared and structurally characterized by single-crystal X-ray diffraction. {[Cu₂(dmmal)₂(edin)(H₂O)₂]·3H₂O}_n (1, edin = N,N′-(ethane-1,2-diyl)diisonicotinamide) and {[Cu₂(dmmal)₂(bdin)(H₂O)₂]·2H₂O}_n (2, bdin = N,N′-(butane-1,4-diyl)diisonicotinamide) both show (6,3) herringbone layers constructed from the edin pillaring of [Cu(H₂O)(dmmal)]_n chain motifs, that feature embedded equatorial-equatorial bridged {Cu(OCO)}_n chains. [Cu₂(dmmal)₂(bpmp)]_n (3, bpmp = bis(4-pyridylmethyl)piperazine) shows a decorated (4,4) grid topology built from bpmp pillared [Cu₂(dmmal)₂]_n ribbon motifs, that feature embedded {Cu₂(OCO)₄} paddlewheel dimeric units. [Cu₂(dmmal)₂(bpfp)]_n (4, bpfp = bis(4-pyridylformyl)piperazine) shows a 5-connected non-interpenetrated 3D 4⁴6⁶ sqp topology, formed from the bpfp pillaring of rectangular equatorial-equatorial bridged [Cu₂(dmmal)₂]_n layers. Variable temperature magnetic studies were carried out on 1, 2 and 4, indicating predominant ferromagnetic superexchange within their equatorial-equatorial {Cu(OCO)}_n chain motifs.

Full text of DOI:10.1016/j.poly.2019.06.018

Accepted Manuscript
Structural diversity and variable temperature magnetic properties in copper di-
methylmalonate coordination polymers containing dipyridyl-type coligands
Colton J. Kalman, Brandon S. Stone, Robert L. LaDuca
PII:
S0277-5387(19)30429-2
https://doi.org/10.1016/j.poly.2019.06.018
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DOI:
Reference:
Polyhedron
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Accepted Date:
15 April 2019
4 June 2019
10 June 2019
Please cite this article as: C.J. Kalman, B.S. Stone, R.L. LaDuca, Structural diversity and variable temperature
magnetic properties in copper dimethylmalonate coordination polymers containing dipyridyl-type coligands,
Polyhedron (2019), doi: https://doi.org/10.1016/j.poly.2019.06.018
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Structural diversity and variable temperature magnetic properties in copper dimethylmalonate
coordination polymers containing dipyridyl-type coligands
Colton J. Kalman, Brandon S. Stone, Robert L. LaDuca*
Lyman Briggs College and Department of Chemistry
Michigan State University, East Lansing, MI 48825 USA
Keywords: crystal structure; coordination polymer; copper; ferromagnetism

Abstract
Four copper dimethylmalonate (dmmal) phases containing long-spanning dipyridyl coligands
have been prepared and structurally characterized by single-crystal X-ray diffraction.
{[Cu2(dmmal)2(edin)(H2O)2]·3H2O}n (1, edin = N,N-(ethane-1,2-diyl)diisonnicotinamide) and
{[Cu2(dmmal)2(bdin)(H2O)2]·2H2O}n (2, bdin = N,N-(butane-1,4-diyl)diisonnicotinamide) both
show (6,3) herringbone layers constructed from the edin pillaring of [Cu(H2O)(dmmal)]n chain
motifs, that feature embedded equatorial-equatorial bridged {Cu(OCO)}n chains.
[Cu2(dmmal)2(bpmp)]n (3, bpmp = bis(4-pyridylmethyl)piperazine) shows a decorated (4,4) grid
topology built from bpmp pillared [Cu2(dmmal)2]n ribbon motifs, that feature embedded
{Cu2(OCO)4} paddlewheel dimeric units. [Cu2(dmmal)2(bpfp)]n (4, bpfp = bis(4-
pyridylformyl)piperazine) shows a 5-connected non-interpenetrated 3D 4466 sqp topology,
formed from the bpfp pillaring of rectangular equatorial-equatorial bridged [Cu2(dmmal)2]n
layers. Variable temperature magnetic studies were carried out on 1, 2 and 4, indicating
predominant ferromagnetic superexchange within their equatorial-equatorial {Cu(OCO)}n chain
motifs.

1. Introduction
Three-component coordination polymers that are constructed divalent metal cations,
anionic dicarboxylate ligands, and dipodal neutral organic coligands have shown many intriguing
properties in technologically or medically useful applications [1], such as hydrogen storage [2],
small molecule separation [3], drug delivery [4], heterogeneous catalysis for organic
transformations [5], carbon dioxide sequestration [6], and interesting temperature-dependent and
field-dependent magnetic properties [7]. Additionally, the wide variety of aesthetic structural
topologies continues to provide impetus for further exploratory synthesis [8].
The short-spanning dicarboxylate ligand malonate (mal) has been employed to prepare
copper coordination polymers that exhibit a diversity of magnetic properties. The mal ligand has
a remarkable ability to access numerous chelating and bridging and chelating modes (anti-anti,
anti-syn, syn-syn, 1,3-chelating, etc.) that can provide varied overlap mechanisms for the
magnetic orbitals on adjacent metal centers [9–23]. Variations in preparative conditions can
impart tremendous differences in the structure and magnetic properties of copper malonate
coordination polymers [9]. {[Cu(H2O)3][Cu(mal)2(H2O)]}n shows coordination polymer chain
motifs with anti-syn bridges, resulting in intrachain ferromagnetism. The more complicated
phase {[Cu(H2O)4]2[Cu(mal)2(H2O)][Cu(mal)2(H2O)2]{[Cu(H2O)4] [Cu(mal)2(H2O)2]} has
mono-, di-, and trinuclear species coexisting in the same single crystal, with weak ferromagnetic
coupling within the dinuclear and trinuclear species [9]. Increased structural diversity can be
achieved in copper malonate phases by incorporation of neutral coligands.
[Cu2(mal)2(H2O)2(bpy)]n (bpy = 4,4-bipyridine) displays [Cu4(mal)4] squares with anti-syn

bridging carboxylates, linked into a coordination polymer layer by the tethering bpy ligands;
moderately strong ferromagnetic superexchange is observed within the square subunits [10].
Employing the kinked, hydrogen-bonding capable 4,4-dipyridylamine (dpa) ligand
resulted in the 2-D herringbone structure {[Cu2(mal)2(dpa)(H2O)2]•H2O}n, which showed
competing anti-anti and anti-syn carboxylate bridging modes and net weak ferromagnetism [11].
The longer-spanning 1,2-di(4-pyridyl)ethane (dpe) ligand afforded {[Cu3(mal)2(dpe)3(H2O)2]
(NO3)2(H2O)2}n, which shows a 4,6-connected 3-D topology and modest ferromagnetic coupling
between anti-syn carboxylate bridged copper ions [12]. {[Cu(dpp)(mal)(H2O)] •4H2O}n (dpp =
1,3-di(4-pyridyl)propane) possesses a simple 1-D chain structure with bridging dpp ligands and
1,3-chelating capping malonates [13], along with discrete pentameric water molecule chains that
include the aqua ligands.
When compared to the number of divalent copper coordination polymers built from
malonate ligands, those containing substituted malonate ligands such as methylmalonate (mmal),
or dimethylmalonate (dmmal) are rarer [24–27]. Still, these materials can show the same
synthesis-dependent structural and magnetic property diversity as seen in coordination polymers
based on unsubstituted malonate ligands. {[Cu(bpy)2][Cu(bpy)2(mmal)(NO3)(H2O)](NO3)
·3.5H2O}n manifests [Cu(bpy)2]n2n+ square grid motifs pillared by mmal ligands into a 3-D pcu
net [24], with net antiferromagnetism produced from competing ferromagnetic and
antiferromagnetic interactions across the different binding modes of the mmal carboxylate
termini. The related chain phase [Cu(bpy)2(mmal)(H2O)]•H2O}n shows extremely weak
antiferromagnetic coupling through the full span of the mmal ligands [24], while
[Cu2(bpy)(mmal)2(H2O)2]n is a 3-D phase that exhibits ferromagnetic coupling within Cu(mmal)
corrugated layers featuring anti-syn carboxylate bridges [25]. Adjustment of the steric bulk of

the malonate ligand in the case of copper/dpa containing phases imparted marked structural
deviations. Contrasting with the 2-D phase {[Cu2(mal)2(dpa)(H2O)2]•H2O}n,
{[Cu(mmal)(Hmmal)(Hdpa)]•H2O}n possesses 1-D coordination polymer chain motifs
containing {Cu(OCO)}n chains, which exhibit antiferromagnetic coupling mediated by its anti-
syn bridging carboxylates [26]. The dmmal derivative {[Cu3(dmmal)2(dpa)3](ClO4)2•2H2O}n
manifests an antiferromagnetic trimer-based network with a unique 4,5-connected binodal gaf
(4462)(4664)2 topology [26].
Slow diffusion of an ethanolic solution of bpy into an aqueous solution of copper
dimethylmalonate afforded two different coordination polymer complexes as time elapsed [27].
A small amount of light blue crystals of {[Cu2(dmmal)2(bpy)1.5(H2O)]•2H2O}n were initially
formed at the solution interface. This material displayed a 3,4-connected 2D layer with an
unprecedented (426)(42638) topology containing alternating rows of hexagonal and rectangular
ring units. These crystals dissolved as the reaction continued, as darker blue crystals of the
thermodynamic product {[Cu3(dmmal)3(bpy)3(H2O)4]•H2O}n were formed. This latter phase
manifested a 4-connected 3D 658 cds topology.
In this study, we have aimed to expand the structure scope of copper dimethylmalonate
coordination polymers by employing the longer spanning hydrogen-bonding capable dipyridyl
ligands N,N-(ethane-1,2-diyl)diisonicotinamide) (edin), N,N-butane-1,4-diyl)diisonicotinamide)
(bdin), bis(4-pyridylmethyl)piperazine (bpmp), and bis(4-pyridylformyl)piperazine (bpfp). All
four of these coligands have afforded coordination polymers with intriguing topologies in the
recent past [28–30]. Herein we discuss the synthesis, structural characterization, thermal
properties, and variable temperature magnetic susceptibility behavior of

{[Cu2(dmmal)2(edin)(H2O)2]·3H2O}n (1), {[Cu2(dmmal)2(bdin)(H2O)2]·2H2O}n (2),
[Cu2(dmmal)2(bpmp)]n (3), and [Cu2(dmmal)2(bpfp)]n (4).
2. Experimental Section
2.1 General Considerations
Copper dimethylmalonate was prepared by adaptation of a literature procedure for the
synthesis of copper malonate [31] via substitution of malonic acid with dimethylmalonic acid.
Dimethylmalonic acid was commercially obtained from TCI America. N,N-(ethane-1,2-
diyl)diisonnicotinamide (edin) was prepared by condensation of 1,2-ethylenediamine and two
molar equivalents of isonicotinoyl chloride hydrochloride in dry pyridine. The reaction mixture
was quenched with water, and then the product was isolated via CH2Cl2 extraction and removal
of solvent in vacuo [32]. A similar process, employing 1,4-butanediamine as a precursor,
afforded the bdin ligand. Bis(4-pyridylformyl)piperazine (bpfp) [33] and bis(4-
pyridylmethyl)piperazine (bpmp) [34] were prepared by literature procedures. Water was
deionized above 3MΩ–cm in-house. IR spectra were recorded on powdered samples using a
Perkin Elmer Spectrum One DRIFT instrument. UV-Visible spectra were recorded on a
Shimadzu UV-2600 spectrophotometer. Thermogravimetric analysis was performed on a TA
Instruments Q-50 Thermogravimetric Analyzer with a heating rate of 10 °C/min up to 600 °C.
Elemental Analysis was carried out using a Perkin Elmer 2400 Series II CHNS/O Analyzer.
Variable temperature magnetic susceptibility data (2 K to 300 K) for 1–4 were collected on a
Quantum Design MPMS-3 SQUID magnetometer at an applied field of 0.1 T. After each
temperature change the sample was kept at the new temperature for 5 minutes before

magnetization measurement to ensure thermal equilibrium. The susceptibility data was corrected
for diamagnetism using Pascal’s constants [35].
2.2 Preparation of {[Cu2(dmmal)2(edin)(H2O)2]·3H2O}n (1)
Copper dimethylmalonate (18 mg, 0.094 mmol), was dissolved in 3 mL deionized water in a 15
mL glass vial. A 2 mL aliquot of a 1:1 ethanol:water mixture was layered carefully on top of the
copper dimethylmalonate solution. A 3 mL ethanol solution containing edin (23 mg, 0.094
mmol) was then added to the reaction vial. After allowing the reaction mixture to stand
undisturbed for 7 d, dark blue crystals of 1 were deposited at the bottom of the vial. The crystals
were collected by decantation and washed with water and acetone, affording 20 mg of 1 (57 %
yield based on Cu). Anal. Calc. for C24H36Cu2N4O15 1: C, 38.55; H, 4.85; N, 7.49 %. Found: C,
38.45; H, 4.97; N, 7.11%. IR (cm-1): 3500 (w, br) 1634 (s), 1580 (s), 1541 (s), 1435 (m), 1312
(w), 1065 (m), 854 (w), 764 (m).
2.3 Preparation of {[Cu2(dmmal)2(bdin)(H2O)2]·2H2O}n (2)
Copper dimethylmalonate (18 mg, 0.094 mmol), was dissolved in 3 mL deionized water in a 15
mL glass vial. A 2 mL aliquot of a 1:1 ethanol:water mixture was layered carefully on top of the
copper dimethylmalonate solution. A 3 mL ethanol solution containing bdin (25 mg, 0.094
mmol) was then added to the reaction vial. After allowing the reaction mixture to stand
undisturbed for 7 d, dark blue crystals of 2 were deposited at the bottom of the vial. The crystals
were collected by decantation and washed with water and acetone, affording 22 mg of 2 (61 %
yield based on Cu). Anal. Calc. for C26H38Cu2N4O14 2: C, 41.21; H, 5.06; N, 7.39%. Found: C,
41.55; H, 5.01; N, 7.62%. IR (cm-1): 3500 (w, br), 1628 (s), 1575 (s), 1543 (s), 1460 (m), 1435

(m), 1369 (w), 1315 (s), 1201 (w), 1063 (m), 904 (m), 859 (m), 798 (w), 764 (m), 696 (s), 682
(s).
2.4 Preparation of [Cu2(dmmal)2(bpmp)]n (3)
Copper dimethylmalonate (18 mg, 0.094 mmol), was dissolved in 3 mL deionized water in a 15
mL glass vial. A 2 mL aliquot of a 1:1 ethanol:water mixture was layered carefully on top of the
copper dimethylmalonate solution. A 3 mL ethanol solution containing bpmp (25 mg, 0.094
mmol) was then added to the reaction vial. After allowing the reaction mixture to stand
undisturbed for 7 d, blue crystals of 3 were deposited at the bottom of the vial. The crystals were
collected by decantation and washed with water and acetone, affording 17 mg of 3 (55 % yield
based on Cu). Anal. Calc. for C26H32Cu2N4O8 3: C, 47.63; H, 4.91; N, 8.54 %. Found: C, 47.44;
H, 5.12; N, 8.38%. IR (cm-1): 1610 (s), 1591 (s), 1458 (w), 1427 (s), 1339 (m), 1168 (w), 1132
(w), 1066 (w), 1011 (m), 842 (m), 800 (m), 695 (m).
2.5 Preparation of [Cu2(dmmal)2(bpfp)]n (4)
Copper dimethylmalonate (18 mg, 0.094 mmol), was dissolved in 3 mL deionized water in a 15
mL glass vial. A 2 mL aliquot of a 1:1 ethanol:water mixture was layered carefully on top of the
copper dimethylmalonate solution. A 3 mL ethanol solution containing bpfp (28 mg, 0.094
mmol) was then added to the reaction vial. After allowing the reaction mixture to stand
undisturbed for 7 d, dark blue crystals of 4 were deposited at the bottom of the vial. The crystals
were collected by decantation and washed with water and acetone, affording 15 mg of 4 (47 %
yield based on Cu). Anal. Calc. for C26H28Cu2N4O10 4: C, 45.68; H, 4.13; N, 8.20 %. Found: C,
45.59; H, 4.08; N, 8.47%. IR (cm-1): 1639 (s), 1579 (w), 1548 (s), 1431 (s), 1350 (m), 1259 (m),
1157 (w), 1006 (m), 893 (w), 846 (m), 733 (w), 689 (m).

3. X-ray Crystallography
Diffraction data for 1–4 were collected on a Bruker-AXS SMART-CCD X-ray
diffractometer using graphite-monochromated Mo-Kα radiation (λ= 0.71073 Å) at 173 K. The
data were processed via SAINT [36], and corrected for both Lorentz and polarization effects and
absorption effects using SADABS [37]. The structures were solved using direct methods with
SHELXTL [38] within the OLEX2 crystallographic software suite [39]. All non-hydrogen
atoms were refined anisotropically. Hydrogen atoms were placed in calculated positions and
refined isotropically with a riding model. Crystallographic details for 1–4 are given in Table 1.
4. Results and Discussion
4.1 Synthesis and Spectra
Crystalline samples of 1–4 were produced by slow diffusion of aqueous solutions of copper
dimethylmalonate with ethanol solutions of the requisite dipyridyl ligand. The infrared spectra of
1–4 were consistent with their structural components as determined by single-crystal X-ray
diffraction. Intense, broad asymmetric and symmetric C–O stretching bands within the
dimethylmalonate ligands were observed at 1541 and 1435 cm−1 for 1, 1548 and 1435 cm−1 for 2,
1591 and 1427 cm−1 for 3, and 1548 and 1431 cm−1 for 4. Moderate intensity bands in the range
of ~1600 cm−1 to ~1300 cm−1 are attributed to the stretching modes of the pyridyl rings of the
dipyridylamide ligands [40]. Features corresponding to C–H bending and ring puckering within
the pyridyl moieties exist in the region between ~900 and ~650 cm−1. Broad, weak spectral

bands in the vicinity of ~3000–3400 cm−1 indicate the presence of unbound water molecules in
the spectra of 1. The carbonyl stretching bands for the dipyridylamide ligands edin, bdin, and
bpfp appeared at 1634 cm−1 for 1, 1628 cm−1 for 2, and 1639 cm−1 for 4, respectively.
4.2 Structural description of {[Cu2(dmmal)2(edin)(H2O)2]·3H2O}n (1)
Compound 1 crystallized in the acentric space group P21 with a Flack parameter of
–0.026(9) [41] indicating mostly complete enantiomorphic purity within the crystal. Its
asymmetric unit consists of two divalent copper atoms (Cu1, Cu2), two crystallographically
distinct dmmal ligands, a full edin ligand, two bound water molecules and three water molecules
of crystallization. Both Cu1 and Cu2 atoms adopt a {CuO4N} distorted square pyramidal
coordination geometry, with trigonality  factors [42] of 0.16 and 0.14, respectively. Bound
water molecules occupy the elongated axial z direction position in both d9 Jahn-Teller distorted
coordination environments. The basal planes at both Cu1 and Cu2 contain an edin pyridyl
nitrogen donor atom situated cis to a single dmmal carboxylate oxygen donor atom. The
remaining two cis coordination sites at each Cu1 and Cu2 contain a 1,3-chelating arrangement of
dmmal oxygen donor atoms. A thermal ellipsoid plot of both square pyramidal coordination
environments is shown in Fig. 1. Pertinent bond lengths and angles at the two different copper
atoms are listed in Table 2. Crystallographic distinction between Cu1 and Cu2 is enforced by
different metrical parameters.
The dmmal ligands in 1 adopt an 2-3-O,O:O exobidentate binding mode, in which
one copper atom is bound in a 1,3-chelating fashion by two dmmal carboxylate oxygen atoms,
and the other copper atom is bound by a third dmmal carboxylate oxygen atom in a monodentate
fashion. One dmmal carboxylate oxygen atom remains unligated. [Cu(H2O)(dmmal)]n chain

motifs with embedded {Cu(OCO)}n chain submotifs (Fig. 2), based on Cu1 (chain-A) or Cu2
(chain-B), are constructed via dmmal binding and bridging and are situated parallel to the b
crystal direction. The dmmal carboxylate groups connect coordination sites on adjacent copper
atoms, resulting in equatorial-equatorial anti-syn carboxylate bridges. Within the chain-A
motifs, the Cu1···Cu1 internuclear distance is 4.862(3) Å, while the related Cu2···Cu2 distance
within the chain-B motifs measure 4.915(3) Å. Within each chain motif, the next nearest
Cu···Cu distance of 7.115(4) Å represents the b lattice parameter.
Adjacent chain-A and chain-B motifs in 1 are pillared by edin ligands into
[Cu (dmmal) (edin)(H O) ] coordination polymer layers that are arranged parallel to the ( 0 2)
1
2
2
2
2 n
crystal planes (Fig. 3). The edin ligands have an anti conformation of their central N–C–C–N
linkages, and span a Cu1···Cu2 internuclear distance of 17.64(1) Å. Treating the copper atoms in
the layer motif of 1 as 3-connected nodes results in an underlying (6,3) herringbone topology.
Neighboring [Cu2(dmmal)2(edin)(H2O)2]n layers stack in an AAA pattern along the a crystal
direction (Fig. S1), mediated by hydrogen bonding patterns involving pairs of water molecules of
crystallization in the interlamellar regions (Table S1). The water molecules of crystallization
occupy incipient 1D channels that comprise 4.1 % of the unit cell volume according to PLATON
[43].
4.3 Structural description of {[Cu2(dmmal)2(bdin)(H2O)2]·2H2O}n (2)
In contrast to 1, compound 2 crystallized in a centrosymmetric monoclinic space group
with an asymmetric unit containing a divalent copper atom, a fully deprotonated dmmal ligand, a
bound water molecule, half of a bdin ligand whose central C–C bond is sited over a

crystallographic inversion center, and a water molecule of crystallization. The copper atoms in 2
adopt a {CuO4N} distorted square pyramidal coordination geometry, with a trigonality  factor
of 0.092. The bound water molecule occupies the axial coordination site, while the basal plane is
occupied by a bdin pyridyl nitrogen donor atom sited cis to a single dmmal carboxylate oxygen
donor atom. The remaining two cis coordination sites contain a 1,3-chelating arrangement of
carboxylate oxygen donor atoms belonging to the same dmmal ligand. A thermal ellipsoid plot
of both square pyramidal coordination environments is shown in Fig. 4a. Relevant bond lengths
and angles in the coordination sphere are listed in Table 3.
The dmmal ligands in 2 adopt an 2-3-O,O:O exobidentate binding mode identical to
that in 1, in which one copper atom is bound in a 1,3-chelating fashion by two dmmal
carboxylate oxygen atoms, and the other copper atom is bound by a third dmmal carboxylate
oxygen atom in a monodentate fashion. One dmmal carboxylate oxygen atom remains unligated.
[Cu(H2O)(dmmal)]n chain motifs with embedded {Cu(OCO)}n chain submotifs (Fig. 4b). The
dmmal carboxylate groups connect basal coordination sites on adjacent copper atoms, resulting
once again in equatorial-equatorial anti-syn carboxylate bridges. The Cu···Cu internuclear
distances within the chain motifs in 2 measure 4.789 Å. The next nearest Cu···Cu distance of
6.212(3) Å represents the b lattice parameter, and it is virtually 1 Å shorter than the comparable
distance in 1. The [Cu(H2O)(dmmal)]n chain motifs in 2 are pillared by bbin ligands that span a
Cu···Cu internuclear distance of 18.18(1) Å, to form a 2D [Cu2(dmmal)2(bdin)(H2O)2]n layer
(Fig. 5). The central tethers of the bdin ligands manifest a gauche-anti-gauche conformation,
with torsion angles of 65.8, 180, and 65.8°. As is the case for 1, considering the copper atoms in
the layer motif of 2 as 3-connected nodes results in a (6,3) herringbone topology framework.
Neighboring [Cu2(dmmal)2(bdin)(H2O)2]n layers stack in an AAA pattern along the a crystal

direction, mediated by hydrogen bonding patterns involving bound water molecules and bdin
formyl groups (Fig. S2, Table S1).
4.4 Structural description of [Cu2(dmmal)2(bpmp)]n (3)
The asymmetric unit of compound 3 is comprised of a divalent copper atom, a dmmal
ligand, and half of a bpmp ligand whose piperazinyl ring centroid is situated on a
crystallographic inversion center. As in 1, the copper atoms in 3 adopt a {CuO4N} square
pyramidal coordination geometry, but with a significantly decreased distortion from idealized
geometry as evidenced by a trigonality  factor of 0.002. Single carboxylate oxygen atom
donors from four dmmal ligands occupy the basal plane within the coordination environment,
and a bpmp pyridyl nitrogen donor atom fills the apical position (Fig. 6a). Bond lengths and
angles within the square pyramidal coordination environment are listed in Table 3.
The dmmal ligands in 3 adopt an 4-4-O:O:O:O exotetradentate binding mode,
constructing [Cu2(dmmal)2]n ribbon motifs (Fig. 6b) with embedded {Cu2(OCO)4} paddlewheel
dimeric units in which the internuclear Cu···Cu distance measures 2.6308(9) Å. The closest
Cu···Cu interaction between adjacent paddlewheel dimers measures 6.0865(14) Å, which
denotes the b lattice parameter. Neighboring [Cu2(dmmal)2]n ribbon motifs, aligned parallel to
the b crystal direction, are pillared into [Cu2(dmmal)2(bpmp)]n coordination polymer layers by
bpmp ligands (Fig. 6c). These dipyridyl coligands span a Cu···Cu distance of 15.83(1) Å.
Treating the {Cu2(OCO)4} paddlewheels as 4-connected nodes reveals an underlying (4,4) grid
topology for the layer motifs in 3. The [Cu2(dmmal)2(bpmp)]n layers, which are coincident with
the bc crystal planes, stack in an ABAB pattern along the a crystal direction (Fig. S3).

Supramolecular impetus for this stacking pattern is provided by non-classical C–H···O hydrogen
bonding donation from pyridylmethylene C–H groups to dmmal carboxylate oxygen atoms
(C···O distance = 3.634(2) Å).
4.5 Structural description of [Cu2(dmmal)2(bpfp)]n (4)
The asymmetric unit of compound 4 contains a divalent copper atom, a fully
deprotonated dmmal ligand, and half of a bpfp ligand whose piperazinyl ring centroid is sited
over a crystallographic inversion center. The copper atoms are ligated in a {CuO4N} square
pyramidal fashion (t = 0.015), with a pyridyl nitrogen donor atom from the bpfp ligand
occupying the apical position. The basal plane is comprised of single carboxylate oxygen donor
atoms from four dmmal ligands. A thermal ellipsoid representation of the coordination
environment is shown in Fig. 7a. Relevant bond lengths and angles are listed in Table 5.
The copper atoms are connected to four others by dmmal ligands to construct
[Cu2(dmmal)2]n layer motifs in 4 (Fig. 7b). All the dmmal carboxylate groups bridge equatorial
sites on neighboring copper atoms, with Cu···Cu distances of 5.022(2) and 5.214(2) Å. Adjacent
[Cu2(dmmal)2]n layers are pillared by bpfp ligands to construct a non-interpenetrated 3D
[Cu2(dmmal)2(bpfp)]n coordination polymer network (Fig. 8a). The Cu···Cu distance spanned by
the dipodal bpfp ligand is 15.999(4) Å. According to TOPOS [44], the resulting 3D net possesses
a 5-connected 4466 sqp topology (Fig. 8b) [14]. This net resembles a 6-connected pcu topology
with every node having a single absent pillar in a regular fashion.

4.6 Thermal Properties
Compound 1 underwent complete dehydration between 25 and 205 °C, with a mass loss of 12.5
% corresponding well with the predicted value of 12.1 % for five molar equivalents of water.
Ejection of organic components occurred above 205 °C. Compound 2 underwent complete
dehydration between 25 and 190 °C, with a mass loss of 9.9 % corresponding well with the
predicted value of 9.5 % for four molar equivalents of water. Ejection of organic components
occurred above 190 °C. Compound 3 underwent some decarboxylation up to 140 °C, with a
mass loss of 11.2 % roughly corresponding to the elimination of two molar equivalents of CO2
(13.4 % calc’d). Ejection of additional organic components occurred above 140 °C. Compound 4
underwent some decarboxylation between 25 and 210 °C, with a mass loss of 6.6 %
corresponding to the elimination of one molar equivalent of CO2 (6.4 % calc’d). Ejection of
additional organic components occurred above 210 °C. TGA traces for 1–4 are shown in Figs.
S4–S7, respectively.
4.7 Variable temperature magnetic properties
Variable temperature magnetic susceptibility measurements were carried out on
polycrystalline samples of 1, 2, and 4, to probe the magnitude of magnetic superexchange
between carboxylate bridged divalent copper atoms. As equatorial-equatorial bridged
{Cu2(OCO)4} paddlewheel dimeric units in previously reported coordination polymers manifest
strong antiferromagnetic coupling in all cases due to direct -like interactions of the magnetic
dx2–y2 orbitals [45], a variable temperature magnetic study on 3 would simply be a verification
experiment. As a result, such a study was not undertaken.
For compound 1, the mT value of 0.76 cm3-K/mol at 300 K was consistent with the
expected value for two uncoupled S = 1/2 spins per formula unit, assuming an idealized value of

g = 2. The mT value slowly increased on lowering of temperature, reaching 0.81 cm3-K/mol at
150 K and 0.88 cm3-K/mol at 60 K. The mT product then increased more rapidly with
decreasing temperature, attaining a value of 1.01 cm3-K/mol at 25 K and 1.31 cm3-K/mol at 10
K. The mT value measured 2.00 cm3-K/mol at 3 K. The shape of the mT vs. T graph indicates
ferromagnetic coupling along the equatorial-equatorial bridged carboxylates in the 1D
{Cu(OCO)}n chain submotifs in 1. The magnetic susceptibility data for 1 were also fit to Baker’s
series expansion [46] for an isotropic Heisenberg 1-D S = 1/2 chain (eq. 1). The best fit to the
observed data (Fig. 9) gave g = 2.06(2), and J = 3.0(2) cm–1 with R = 1.1  10–3 = {[(m T)obs
(mT)calc]2/[(mT)obs]2}. The positive value of J corroborates the contention of ferromagnetic
superexchange in 1.
–
For compound 2, the mT value of 0.75 cm3-K/mol at 300 K matches the exact expected
value for two uncoupled S = 1/2 spins per formula unit, assuming an idealized value of g = 2.
The mT value slowly increased on lowering of temperature, reaching 0.87 cm3-K/mol at 80 K
and 1.01 cm3-K/mol at 30 K. The mT product then increased more rapidly with decreasing
temperature, attaining a value of 1.37 cm3-K/mol at 10 K, and 2.00 cm3-K/mol at 3 K. The shape
of the mT vs. T graph indicates ferromagnetic coupling along the equatorial-equatorial bridged
carboxylates in the 1D {Cu(OCO)}n chain submotifs in 2, as seen in 1, which possessed similar
submotifs. The best fit to the observed data (Fig. 10) using Baker’s expression (eq. 1) gave g =
2.08(3), and J = 3.3(3) cm–1 with R = 1.6  10–3. The positive value of J denotes ferromagnetic
superexchange in 2.
2
3
푁푔2훽2 퐴
휒푚푇 =
( )
4푘
퐵
푤ℎ푒푟푒 퐴 = 1 + 5.797991푥 + 16.902563푥2 + 29.376885푥3 + 29.832959푥4

푎푛푑 퐵 = 1 + 2.7979916푥 + 7.0086780푥2 + 8.6538644푥3 + 4.5743114푥4
with 푥 = 퐽/푘푇 (eq. 1)
For compound 4, the mT value of 0.75 cm3-K/mol at 300 K was consistent with the
expected value for two uncoupled S = 1/2 spins per formula unit. From 300 K down to 100 K,
the mT value largely remained constant. Below 100 K, the mT value began to increase, reaching
0.79 cm3-K/mol at 60 K and 0.87 cm3-K/mol at 15 K. Below 15 K, the mT value decreased,
measuring 0.84 cm3-K/mol at 10 K, 0.64 cm3-K/mol at 5 K, and 0.28 cm3-K/mol at 2 K. The
variable temperature behavior of the mT value indicates a cooperation of ferromagnetic and
antiferromagnetic behavior within the [Cu2(dmmal)2]n equatorial-equatorial bridged layers in 4.
The variable temperature magnetic susceptibility data for 4 was fit to the Baker equation for a
{Cu(OCO)}n chain submotif, modified with a mean-field approximation (eq. 2) to account for
inter-chain spin communication within the {Cu2(OCO)2}n rectangular layer motifs. Given the
two different carboxylate bridged Cu···Cu internuclear distances, use of a quadratic layer model
with just one J exchange integral is inappropriate in the present case. The best fit parameters to
eq. 2 gave g = 1.936(5), J = 4.6(2) cm–1, and zJ = 5.19(6) cm–1, with R = 3.3  10–4. The positive
J parameter indicates ferromagnetic superexchange within parallel {Cu(OCO)}n chain submotifs,
while the negative zJ factor indicates plausible opposite alignment of ferromagnetic spins
between adjacent chain submotifs in 4.
2
3
푁푔2훽2 퐴
휒푚푇 =
( )
4푘
퐵
푤ℎ푒푟푒 퐴 = 1 + 5.797991푥 + 16.902563푥2 + 29.376885푥3 + 29.832959푥4
푎푛푑 퐵 = 1 + 2.7979916푥 + 7.0086780푥2 + 8.6538644푥3 + 4.5743114푥4

휒푚
퐽
푘푇
퐽
푘푇
with 푥 =
, and with 푥 =
and 휒'푚 =
(eq. 2)
1 ‒ 푧퐽'휒푚
5. Conclusions
A series of four copper dimethylmalonate coordination polymers has been prepared via
slow solvent diffusion synthetic methods. The underlying topologies depend crucially on the
nature of the neutral dipyridyl-type coligand. Two longer spanning dipyridylamide ligands, edin
and bdin, afforded (6,3) herringbone type layered structures by linking together {Cu(OCO)}n
chain submotifs. The dipyridylamide ligand bpfp, based on a central piperazinyl tether, afforded
a relatively uncommon 5-connected 3D sqp network, which featured {Cu(OCO)}n chain
submotifs linked into rectangular {Cu2(OCO)2}n layers. The piperazinyl based bpmp ligand,
which lacks any amide functional groups, produced a layer topology with embedded
{Cu2(OCO)4} paddlewheel dimeric units. Ferromagnetic coupling was observed along the
equatorial-equatorial bridged {Cu(OCO)}n chain submotifs wherever these were present.
Supplementary Material
Hydrogen bonding geometric parameters, additional molecular graphics and thermogravimetric
analysis plots. Crystallographic data (excluding structure factors) for 1–4 have been deposited
with the Cambridge Crystallographic Data Centre with Nos. 1891894, 1898478, 1891895,
1891896, respectively. Copies of the data can be obtained free of charge via the Internet at
<https://summary.ccdc.cam.ac.uk/structure-summary-form>.

Acknowledgements
Support for this work was provided by the Honors College of Michigan State University.
We thank Dr. Reza Loloee and Ms Celeste Czarnecki for experimental assistance.

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Table 1. Crystal and Structure Refinement Data for 1–4.
Data
Empirical Formula
Formula Weight
Crystal system
Space group
a (Å)
1
C24H36Cu2N4O15
747.65
2
C26H38Cu2N4O14
757.68
Monoclinic
P21
Monoclinic
P21/n
11.4172(7)
7.1165(4)
19.2092(12)
90
10.8185(17)
6.2125(10)
23.675(4)
90
b (Å)
c (Å)
 (°)
103.9860(10)
90
91.429(2)
90
 (°)
 (°)
V (Å3)
1514.49(16)
2
1590.7(4)
2
Z
D (g cm–3)
 (mm–1)
Min./max. transmission
1.639
1.582
1.482
1.410
0.8949
0.8760
–13 ≤ h ≤ 13,
–8 ≤ k ≤ 8,
–13 ≤ h ≤ 13,
–7 ≤ k ≤ 7,
hkl ranges
–22 ≤ l ≤ 23
–28 ≤ l ≤ 28
Total reflections
Unique reflections
R(int)
12337
5441
12375
2952
0.0328
421
0.0372
214
Parameters
R1 (all data)
R1 (I > 2σ(I))
wR2 (all data)
wR2 (I > 2σ(I))
0.0398
0.0354
0.0831
0.0796
0.0432
0.0372
0.1037
0.0985
Max/min residual
(e–/ Å3)
0.496/–0.456
1.029
0.699/–0.604
1.071
G.O.F.

Table 1. Crystal and Structure Refinement Data for 1–4.
Data
Empirical Formula
Formula Weight
Crystal system
Space group
a (Å)
3
C24H32Cu2N4O8
655.64
4
C24H28Cu2N4O10
683.60
Monoclinic
P21/n
Monoclinic
P21/n
13.877(3)
6.0865(14)
16.588(6)
90
6.5143(7)
29.546(3)
7.0507(8)
90
b (Å)
c (Å)
 (°)
100.062(2)
90
92.4460(10)
90
 (°)
 (°)
V (Å3)
1379.6(6)
2
1355.8(3)
2
Z
D (g cm–3)
 (mm–1)
Min./max. transmission
1.578
1.674
1.597
1.634
0.8996
0.8737
–16 ≤ h ≤ 16,
–7 ≤ k ≤ 7,
–19 ≤ l ≤ 20
–7 ≤ h ≤ 7,
–35 ≤ k ≤ 35,
–8 ≤ l ≤ 8
hkl ranges
Total reflections
Unique reflections
R(int)
10852
2539
11184
2486
0.0385
183
0.0461
192
Parameters
R1 (all data)
R1 (I > 2σ(I))
wR2 (all data)
wR2 (I > 2σ(I))
0.0563
0.0374
0.1095
0.0980
0.0397
0.0305
0.0765
0.0717
Max/min residual
(e–/ Å3)
1.026/–0.326
1.037
0.334/–0.359
1.032
G.O.F.

Table 2. Selected Bond Distance (Å) and Angle (°) Data for 1.
Cu1–O1
1.947(4)
1.945(3)
1.943(4)
2.323(4)
2.019(5)
1.940(4)
1.961(4)
1.933(3)
2.248(4)
2.019(5)
O3–Cu1–O1
O3–Cu1–O2#1
O3–Cu1–O9
O3–Cu1–N1
N1–Cu1–O9
O5–Cu2–O6#2
O5–Cu2–O12
O5–Cu2–N4
90.23(15)
178.21(18)
98.65(15)
88.30(17)
90.71(16)
91.67(15)
86.37(15)
90.35(18)
Cu1–O2#1
Cu1–O3
Cu1–O9
Cu1–N1
Cu2–O5
Cu2–O6#2
Cu2–O8
Cu2–O12
Cu2–N4
O1–Cu1–O9
O1–Cu1–N1
O6#2–Cu2–O12 91.88(17)
O6#2–Cu2–N4
100.53(16) O8#2–Cu2–O5
169.93(17)
178.16(18)
168.76(18) O8#2–Cu2–O6#2 90.17(15)
O2#1–Cu1–O1 90.77(15) O8#2–Cu2–O12 93.71(15)
O2#1–Cu1–O9 82.62(14) O8#2–Cu2–N4
O2#1–Cu1–N1 90.43(17) N4–Cu2–O12
87.82(17)
98.09(17)
Symmetry transformations: #1 –x, y – 1/2, –z; #2 –x + 2, y – 1/2, –z + 1.
Table 3. Selected Bond Distance (Å) and Angle (°) Data for 2.
Cu1–O1
1.9599(19) O2#1–Cu1–O5 88.53(8)
1.9440(18) O2#1–Cu1–N1 90.17(8)
Cu1–O2#1
Cu1–O3
1.9268(19) O3–Cu1–O1
91.17(8)
Cu1–O5
Cu1–N1
O1–Cu1–O5
O1–Cu1–N1
O2#1–Cu1–O1 90.41(8)
2.288(2)
2.015(2)
91.76(8)
O3–Cu1–O2#1 177.54(8)
O3–Cu1–O5
O3–Cu1–N1
89.54(9)
88.52(9)
96.23(9)
172.00(9) N1–Cu1–O5
symmetry transformation: –x + 1/2, y – 1/2, –z + 1/2.

Table 4. Selected Bond Distance (Å) and Angle (°) Data for 3.
Cu1–N1
2.172(3)
1.968(2)
1.963(2)
1.976(2)
1.961(2)
O1–Cu1–O4#1
O1–Cu1–O2#2
O2#2–Cu1–N1
O3#3–Cu1–N1
88.31(11)
90.84(11)
86.02(10)
98.68(10)
Cu1–O4#1
Cu1–O1
Cu1–O2#2
Cu1–O3#3
O4#1–Cu1–N1
O3#3–Cu1–O4#1 89.81(11)
167.94(9)
106.17(10) O3#3–Cu1–O1
O4#1–Cu1–O2#2 167.81(9) O3#3–Cu1–O2#2 88.49(11)
O1–Cu1–N1
93.29(10)
Symmetry transformations: #1 #1 –x + 1, –y + 1, –z + 1; #2 x, y – 1, z;
#3 –x + 1, –y, –z + 1.
Table 5. Selected Bond Distance (Å) and Angle (°) Data for 4.
Cu1–O1
1.9665(17) O3#2–Cu1–O1
92.71(7)
Cu1–O2#1
Cu1–O3#2
Cu1–O4#1
Cu1–N1
1.9637(18) O3#2–Cu1–O2#1 87.37(7)
1.9629(17) O3#2–Cu1–N1
1.9486(18) O4#1–Cu1–O1
86.62(8)
90.32(7)
2.255(2)
86.92(8)
O4#1–Cu1–O2#1 89.52(7)
O4#1–Cu1–O3#2 176.50(7)
O1–Cu1–N1
O2#1–Cu1–O1 177.38(8) O4#1–Cu1–N1
O2#1–Cu1–N1 95.69(8)
95.31(8)
Symmetry transformations: #1 x + 1/2, –y + 3/2, z – 1/2; #2 x, y, z – 1.

Figure 1. Crystallographically distinct {CuO4N} distorted square pyramidal coordination
environments and complete ligand set in 1. Thermal ellipsoids are drawn at 50 % probability.
Symmetry codes are as in Table 2.
Figure 2. [Cu(H2O)(dmmal)]n chain motifs with embedded equatorial-equatorial bridged
{Cu(OCO)}n chains in 1. a) Chain-A motif. b) Chain-B motif. The methyl groups of the dmmal
ligands have been omitted for clarity.

Figure 3. [Cu2(dmmal)2(edin)(H2O)2]n coordination polymer layer in 1. The chain-A and chain-B
motifs are drawn in blue and green, respectively, in the online version of this article.