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Journal ArticleDOI

Interaction between heterobinuclear molecules and nature of the ground spin state in oximato-bridged [CuIIMII]2 bis-binuclear complexes (M=Cu, Ni, Mn): crystal structure of [Cu(pdmg)Ni(Me3[12]N3)(EtOH)](ClO4)2

02 May 1999-Inorganica Chimica Acta (Elsevier)-Vol. 288, Iss: 1, pp 57-68

Abstract: Two new heterobimetallic complexes [Cu(pdmg)Ni(Me 3 [12]N 3 )(CH 3 CH 2 OH)](ClO 4 ) 2 ( 2 ) and [Cu(pdmg)Mn(bipy) 2 ](ClO 4 ) 2 · H 2 O ( 3 ) (H 2 pdmg=3,9-dimethyl-4,8-diazaundeca-3,8-diene-2,10-dione dioxime; Me 3 [12]N 3 =2,4,4-trimethyl-1,5,9-triazacyclododeca-1-ene; bipy=2,2′-bipyridyl) have been prepared and characterized. The structure of 2 has been determined by single-crystal X-ray diffraction methods. It consists of [Cu(pdmg)Ni(Me 3 [12]N 3 )(CH 3 CH 2 OH)] 2+ cations and non-coordinated perchlorate anions. The [Cu(pdmg)(CH 3 CH 2 OH)] complex coordinates to the [Ni(Me 3 [12]N 3 )] 2+ fragment to afford the binuclear unit doubly-bridged by oximato groups in cis arrangement. The coordination geometry around the copper atom is square-pyramidal, whereas the nickel atom exhibits a trigonal-bipyramidal surrounding. The intramolecular Cu–Ni distance is 3.810(6) A. In the crystal, two [Cu II Ni II ] dimeric units are related through an inversion center, giving rise to a bis-binuclear entity with a relatively short intermolecular Cu–Cu separation of 4.175(6) A. Variable-temperature magnetic susceptibility measurements (2.0–300 K) for 2 correspond to an almost isolated Cu(II)Ni(II) pair with an intrapair interaction parameter J =−143.6(2) cm −1 . However, the EPR spectrum at 4.2 K is that of a triplet spin state arising from the interaction between the two doublet spin states within the [Cu II Ni II ] 2 bis-binuclear entity. The magnetic properties of 3 unambiguously reveal the bis-binuclear nature of this compound, as is the case for the related homometallic complex [Cu(pdmg)Cu(bipy)(H 2 O) 2 ](ClO 4 ) 2 · H 2 O ( 1 ). The intra- ( J ) and interpair ( j ) interaction parameters for 3 , as deduced from the analysis of its magnetic susceptibility data in the temperature range 2.0–300 K, are −50.9(2) and 1.50(2) cm −1 , respectively. The field dependence of the magnetization of 3 at 2.0 K corresponds to that of a nonet state arising from the interaction between two quintuplet spin states within the [Cu II Mn II ] 2 bis-binuclear entity. The interaction between the heterobinuclear Cu(II)Mn(II) molecules and its influence on the nature of the ground spin state for 3 are analyzed and discussed in the framework of a spin polarization scheme.

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Research Article
Measuring the Project Management Complexity: The Case of
Information Technology Projects
Rocio Poveda-Bautista ,
1
Jose-Antonio Diego-Mas ,
2
and Diego Leon-Medina
3
1
Institute of Innovation and Knowledge Management (INGENIO) (CSIC-UPV), Universitat Polit
`
ecnica de Val
`
encia,
Camino de Vera s/n, 46022 Valencia, Spain
2
Institute for Research and Innovation in Bioengineering (I3B), Universitat Polit
`
ecnica de Val
`
encia,
Camino de Vera s/n, 46022 Valencia, Spain
3
Departamento de Proyectos de Ingenier
´
ıa, Universitat Polit
`
ecnica de Val
`
encia, Camino de Vera s/n, 46022 Valencia, Spain
Correspondence should be addressed to Rocio Poveda-Bautista; ropobau@upvnet.upv.es
Received 27 October 2017; Accepted 27 February 2018; Published 13 May 2018
Academic Editor: Jos
´
e Ram
´
on San Crist
´
obal Mateo
Copyright ©  Rocio Poveda-Bautista et al. is is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly
cited.
Complex projects require specic project management (PM) competences development. However, while no complex projects have
standards that are recognized to guide their management, complex projects do not have guides to deal with their complexity. To lead
complex projects to success, this complexity must be measured quantitatively and, in our opinion, project management complexity
assessment should be based on existing PM standards. In this work, the main project complexity assessment approaches based
on PM standards are analyzed, observing that International Project Management Association (IPMA) approach is the closest to a
tool that can be used as a complexity quantitative measurement system. On the other hand, several authors have shown that the
inherent complexity of specic kind of projects must be measured in a particular way. e main objective of this research is to
propose a project management complexity assessment tool for IT projects, providing a Complexity Index that measures the impact
that complexity factors inherent to IT projects have under a specic complexity scenario. e tool combines the use of complexity
factors dened by IPMA approach and the use of complexity factors found in the literature to manage inherent complexity of IT
projects. All these factors were validated by expert survey and the tool was applied to a study case.
1. Introduction
Although complexity theory was applied to project man-
agement in the s, the discipline of complexity project
management was unocially launched at the th Inter-
national Project Management Association World Congress
in Shanghai []. Following Bosch-Rekveldt et al. [] who
argue that specic complexities in projects might require spe-
cic competence development, inherent complexity within
projects must be studied in a particular way. In this sense, it
is worth highlighting what Williams [] pointed out, which
indicates the increase in the complexity of projects as one of
the main causes of project failure.
In , Bennett [] already noted the need for an
exceptional level of management in complex projects, as well
as the inadequacy of the implementation of conventional
management systems developed for noncomplex or moder-
ately complex projects in complex projects. As Shenhar []
noted, dierent types of projects require dierent managerial
approaches.
What does complexity means in project management?
A complete review has been recently published which sum-
marizes the development of this concept and the factors
that aect project management complexity []. Some other
authors have developed similar work prior to this one [, ].
Many studies and denitions have been developed on
complexity; however, most of these studies focus only on the
conceptual framework of project complexity and few of such
studies have focused on projects complexity measurement
systems. Moving a step beyond the denition of a conceptual
framework of project complexity, the works of some authors
have suggested factors that aect the complexity in projects,
Hindawi
Complexity
Volume 2018, Article ID 6058480, 19 pages
https://doi.org/10.1155/2018/6058480

Complexity
such as Geraldi et al. [], Bosch-Rekveld et al. [], and
Chapman [], which are based on a systematic review of the
literature, Vidal and Marle [] that proposed a complexity-
driven approach of project management to assist project
management in decision making dening a complexity-
based criteria, and Ireland et al. [] that classied projects
(simple, complicated, and complex projects types A, B, and
C) according their complexity and taking into account the
systems of systems view. ese last ones proposed dierent
leadership styles and management tools for each type of
project.
ese studies mentioned above have focused on iden-
tifying project complexity factors and have built a frame-
work that describes project complexity qualitatively [,
]. Despite the fact that several authors have focused on
measuring project complexity quantitatively [, ], besides
this and in our point of view, these project management
complexity assessment systems should be based on existing
project management (PM) standards to ensure implemen-
tation of recognized competencies and practices in man-
aging complex projects. While no complex projects have
standards supported by various bodies of knowledge (BoK),
Project Management Institute (PMI), International Project
ManagementAssociation(IPMA),andtheAssociationfor
Project Management (APM), complex projects do not yet
have a BoK to guide their development. However, some
of these standards try to evaluate projects in order to
assess their complexity and to look at project managers
competence development in the view of complexity. ese
standards capture the dierent perspectives on complexity
and encompass factors that contribute to project complexity
considering dierent approaches.
e objective of this research is to propose a project
management complexity assessment tool in Information
Technology (IT) projects based on an adequate existing PM
standard in order to measure the specic complexity in
the management of this type of projects. To such end, the
presentworkisdevelopedfollowingthefollowingsections:
in Section , we shall study the main project complexity
assessment approaches based on PM standards as well as
the complexity in IT projects, and the methodology followed
to develop a tool for assessing the complexity of IT project
management will be presented. In Section the proposal
of an IT project management complexity assessment tool is
presented and in Section this tool is applied to a study case.
Finally, in Section , the conclusions and limitation of this
study are shown.
2. Materials and Methods
2.1. Project Complexity Assessment Approaches
Based on PM Standards
(i) PMI Approach. It focuses on structural complexity and
uncertainty issues.
isapproachisbasedontwomainperspectivesabout
structural complexity proposed by Baccarini [], organi-
zational complexity and technological complexity, and the
perspective proposed by Turner and Cochrane [] that
considered uncertainty of objectives and uncertainty of
methods used to achieve the projects goals as important fac-
tors of project complexity. Wood and Ashton [] proposed
a similar complete framework. Later Bosch-Rekveld et al.
[] added environmental complexity to Baccarini proposal
giving rise to their TOE (technological, organizational, and
environmental) framework and, in a similar way, Geraldi el al.
[] highlight structural complexity, uncertainty, and sociopo-
litical elements. Williams [] complemented this complexity
denition with other main aspects of complexity: the number
and interdependence of elements and the uncertainty in goals
and means. Dunovi
´
c et al. [] consider constrains as a third
primary element of a new model of complexity, in addition to
structural complexity and uncertainty.
Otherworkssuchas[,]thatfocustheirresearch
on structural complexity and uncertainty can be integrated
in the PMI approach.
From the perspective of structural complexity and uncer-
tainty, Project Management Institute [] published Navi-
gating Complexity: A Practice Guide as a proposal providing
guidelines to project managers in order to perform a check
of the status of the project assessment in terms of complexity.
rough a questionnaire for which the answer is armative
or negative a scenario of complexity in which the project is
located can be implied.
(ii) IPMA Approach. It is based on Crawford-Ishikura Factor
Table for Evaluating Roles and focused on measures of
competence development in complex project management by
the project manager through complexity factors.
e rst standard measurement tool for complexity in
project management was developed by the Global Alliance
for Project Performance Standards (GAPPS) whose approach
characterises projects based on the management of their
complexity. e framework developed by GAPPS used a tool
called Crawford-Ishikura Factor Table for Evaluating Roles
(CIFTER). is tool is used to dierentiate project manager
roles based on the complexity of managed projects. e
developmentofsuchstandardwascarriedoutbymembers
of the GAPSS []. CIFTER identies seven factors that aect
complexity project management.
As an assessment model of complexity project manage-
ment,IPMAhasdevelopedanimplementationguideforthe
assessment criteria, which transfers and adapts the CIFTER
model to objectively demonstrate the degree of competence
of project managers in complexity project management. Such
adaptation was made under ICRG (IPMA Certication and
Regulations Guidelines) []. e model suggests ten factors
for the assessment of complexity.
Table shows the dierent factors with the description
and the criteria taken into account for the IPMA project
management complexity assessment.
is scheme is used to assess the project management
complexity. Each indicator is rated according to four levels
of complexity: very high complexity (), high complexity (),
low complexity (), and very low complexity ().
On the other hand, the Association for Project Man-
agement (APM) considers, in the Registered Project Profes-
sional Candidate Guidance [], that a project is considered

Complexity
T : IPMA Complexity assessment System for IPMA B (IPMA -L-C) [].
Criteria Description of the criteria High Complexity Low Complexity
() Objectives, Assessment of Results
Mandate and Objective uncertain, vague dened, obvious
Conicting objectives many conicts few conicts
Transparency of mandate and objectives hidden quite transparent
Interdependence of objectives very interdependent quite independent
Number and assessment of results large, multidimensional low, monodimensional
() Interested Parties, Integration
Interested parties, lobbies numerous parties few parties
Categories of stakeholders many dierent few uniform categories
Stakeholder interrelations unknown relations few and well known relations
Interests of involved parties divergent interests comparable interest
() Cultural and social context
Diversity of context diverse homogeneous
Cultural variety multicutural, unknown uniform, well known
Geographic distances distant, distributed close, concentrated
Social span large, demanding small, easy to handle
() Degree of innovation, general conditions
Technological degree of innovation unknown technology known and proven technology
Demand of creativity innovative approach repetitive approach
Scope for development large limited
Signicance on public agenda large public interest public interest low
() Project structure, demand for coordination
Structures to be coordinated numerous structures few structures
Demand of coordination demanding, elaborate simple, straighforward
Structuring of phases overlapping, simultaneous sequential
Demand for reporting multidimensional, comprehensive uni-dimensional, common
() Project organisation
Number of interfaces many few
Demand for communication indirect, demanding, manifold direct, not demanding, uniform
Hierarchical structure multidimensional, matrix structure uni-dimensional, simple
Relations with permanent organisations intensive mutual relations few relations
() Leadership, teamwork, decisions
Number of sub-ordinates many, large control span few, small control span
Team structure dynamic team structure static team structure
Leadersship style adaptive and variable constant and uniform
Decision-making processes many important desicions few important decisions
() Resources incl. nance
Availability of people, material, etc. uncertain, changing available, known
Financial resources many investors and kinds of resources one investor and few kinds of resources
Capital investment large (relative to project of the same kind) low (relative to project of the same kind)
Quantity and diversity of sta high low
() Risk and opportunities
Predictability of risks and opportunities low, uncertain high, quite certain
Risk probability, signicance of impacts high risk potential, large impact low risk potential, low impact
Potential of opportunities limited options for actions many options for actions
Options for action to minimise risks large potential of opportunities low potential of opportunities
() PM methods, tools and techniques
Variety of methods and tools applied numerous, manifold few, simple
Application of standards few common standards applicable common standards applicable
Availability of support no support available much support available
Proportion of PM to total project work high percentage low percentage

Complexity
complex project” if it was highly rated in the following
indicators/criteria (not in priority order): objectives, assess-
ment of results, interested parties, integration, cultural and
social context, degree of innovation, general conditions,
project structure, demand for coordination, project organi-
zation, leadership, teamwork, decisions resources (including
nance), risks (threats and opportunities), and project man-
agement methods, tools, and techniques. APM provides a
project complexity questionnaire to help project managers to
know if they are working on projects considered complex.
It may therefore be stated that APM follows an approach
similar to that of IPMA, and its assessment of complexity is
performedfollowingthesameprocedure.
(iii) e Complex Project Manager Competency Standards
Approach. e International Centre for Complex Project
Management of Australian Government develops in 
the Complex Project Manager Competency Standards [].
is standard denes a methodology for the assessment of
complexity and classication of projects based on their com-
plexity and provides tools to categorize projects by their types
of systems, determine the strategy and appropriate contracts
for the project, and select competent project managers.
is approach is not without criticism, since it is a stan-
dard that, on the one hand, has not satisfactorily established
any measure to assess complexity and, on the other, has
been used as a requirement for project managers to establish
contracts and subcontracts with the Australian government
[].
2.2. Complexity in IT Projects. As we have progressed in
the study of complexity in projects several existing project
management standards have been recognizing the need for
an exceptional level of management in complex projects.
In the same way, there is a need for specic competence
development in specic complexities in projects. In this
sense, several authors have developed measurement methods
of project complexity taking into account dierent frame-
works in specics kinds of projects, such as large engineering
projects [], large infrastructure projects [], construction
projects [], and design projects []. However, there are
no reported researches that focused on the conceptualization
of the IT project complexity construct and studies have not
been found to deepen the complexity of the Information
Technology (IT) industry.
While any industry is exposed to project failure, IT
industry shows being more vulnerable to risk and failure than
other industries. A number of areas related to project risk
management and project failure provide useful study bases
to dene IT project complexity.
era are many studies around IT projects; however
the years of experience of Standish Group developing the
CHAOS report are known. As mentioned in the Standish
Group CHAOS Report [] made on  IT projects, over
%ofprojectsfailedorwerecancelled.isreportshows
that large projects have less chance of success than small ones.
On the other hand, agile or iterative development projects
have more chance of success in comparison with waterfall or
incremental projects. e rst are those whose requirements
and solutions evolve over time according to the need of the
project. e last ones are those that sequentially follow the
phases and deliverables of the project.
Other studies on IT projects go a step further by doing
a root cause analysis and identifying factors which can be
attributed to failure of IT projects [, , ]. Some of
these factors are characteristic of observed tendencies in
project with high extent of complexity. Project managers and
researchers have attributed IT projects unsuccessful to the
complexity of such projects [] and propose the use of agile
organizations and reduce the complexity to achieve success
in IT projects.
Aer a systematic review of the literature, Table sum-
marizes the factors inherent to the complexity of IT projects,
specic to IT sector, and dierent from the complexity factors
used by standard tools to assess any other type of projects.
ese factors have been extracted from studies on project
failure characteristics, abandonment factors, risk factors, and
project factors that aect IT development projects. en,
these factors were grouped according to the IPMA project
management complexity assessment criteria that best dene
them.
As conclusions of the literature review, it is important to
mention that one of the main factors that aects the success
of IT projects is related to the user involvement in project
development. On the other hand, an adequate sponsorship of
the executive management is also important. Another critical
factor is requirements; most projects usually begin with a
clear vision and objectives, but sometimes the requirements
of IT projects are based on product iterations; therefore
it is imperative to increase realistic expectations of project
stakeholders to ensure project success.
Resources and skills are key factors in the success of
the project as well as how new technologies work when
applied (sometimes technologies are not mature enough to
be implemented).
Several studies conrm that iterative and agile meth-
ods (project life cycles) have more success than traditional
approaches. erefore, the methodology used on project
management must be present on any assessment of project
complexity.
2.3. Methodology. From all the approaches used by the
dierent recognized standards in project management, IPMA
approachistheclosesttoatoolthatcanbeusedasacomplex-
ity quantitative measurement system, since it denes factors
and suggests a measurement scale to measure the degree to
which these factors aect the management complexity of the
project.Whileitispartoftheprojectmanagercertication
system, this tool is useful for measuring complexity in
projects as it attempts to conrm that the project manager is
capable of managing complex projects.
For the purpose of our study, a framework for IT
project management complexity assessment is designed. is
framework has as baseline the IPMA project management
complexity assessment, adding or removing (if necessary)
some complexity factors in order to build an assessment
template for IT projects. e proposed factors to be included
on the assessment of IT project complexity were extracted

Complexity
T : IT Projects Complexity factors (literature review).
Group of factors Factors References
Objectives, requirements
and expectations
Clearstatementsofrequirements []
Realistic expectations [, –]
Clear strategic objectives [–, ]
Uncertain and changing
regulatory requirements
[–, ]
Interested Parties,
Integration
User involvement [, , , , , ]
Executive management support [–, –]
Project Sponsor Committed with
project methodology
[, , , , ]
Leadership, teamwork,
decisions
Team motivated by the project [, , , ]
HardWorking,focusedsta [,,,,]
Near shore/o shore teams
involved
[, , , ]
Oshore/near shore teams are
familiar with technical and
business aspects of project
[, , , , ]
PM methods, tools and
techniques
Incremental or iterative
methodology used in the project
[, ]
Technology
Incompetence on using/applying
Technology
[, ]
New Technologies [, , , , , , ]
IT Management Support [, ]
TechnologyIlliteracy [,,,,,]
Infrastructure,
Telecommunication Constraints
[, , –]
considering the literature review carried out in section before
and taking into account the fact that IPMA complexity factors
do not focus exclusively on the scope of IT projects but cover
a wider range of projects.
To propose an assessment template in order to build a
tool that measures IT project complexity taking into account
the inherent complexity of these projects, rst, some IT
complexity factors that are not covered by IPMA assessment
will be added to the baseline IPMA assessment knowledge
and, then, this template was validated by experts. is
tool was called Complexity Index tool because it will allow
measuringthecomplexitylevelofaprojectatonepointunder
a scenario of concrete project complexity.
is proposal was validated with a survey fullled by
experts. e selection of the experts was an important issue.
We were looking for IT specialists with deep experience
working in IT projects: IT chiefs technology ocer, IT
project/program managers, project team members, end users,
and practitioners with enough expertise and knowledge on IT
sector. ese experts were involved in the survey under the
below channels: personal contact and social networks.
2.3.1. Selection of IT Project Management Complexity Factors.
We considered all the factors found in the literature as
relevant factors in the complexity of IT projects (see Table ),
since all these factors were identied by several authors as
inherent to the complexity of these projects. All of them were
included in the template developed to design the complexity
assessment tool (see columns and of Table ).
2.3.2. Survey Design. e objective of the survey was to ask
the experts to identify the main complexity factors that aect
IT development projects. e sections below will describe
more in detail the structure of the questions and their
objectives.
Experts Prole Questions. ese questions were designed
to know the experts prole: industrial sector of the IT
practitioner, years of experience working on IT projects, and
professional prole.
Questions Related to Complexity Groups.Questionswere
raised about complexity groups, to nd out those which were
considered by experts as the ones which impacted the most
the complexity of the project.
e complexity groups were assessed using a -point
Likert type scale.
Questions Related to Complexity Factors within Each Group.
e experts were asked about the groups in which new
complexity factors were added. ese are objectives, require-
ments and expectations, interested parties and integration,
leadership, teamwork and decisions, PM methods, tools and
techniques, and technology.

Citations
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Phalguni Chaudhuri1Institutions (1)
Abstract: The strategy of using ‘metal oximates’ building blocks as ligands to synthesize various homo- and hetero-metal paramagnetic complexes is reviewed. The modular approach with ‘metal-complexes’, in this case ‘metal-oximates’, as ligands enables the synthesis of symmetrical, asymmetrical, and linear complexes, viz. MAMB, MAMBMA, MAMBMBMA (MA, MB being two different metal ions). Even the synthesis of asymmetric heterotrinuclear complexes with MAMBMC cores and of MA(μ3-O)2MB butterfly cores has been achieved. This article is focused on such exchange coupled polymetallic, both homo- and hetero-metallic, systems containing the bridging core MNOM′ with an aim to delineate the exchange mechanism through the bridging oximates. The uniqueness of oximates providing diatomic NO-bridging is demonstrated by several series of isostructural complexes with different terminal metal ions like Fe(III), Mn(III), Mn(IV) and Cr(III). Such isostructural series are not available for any other bridging ligands. A qualitative rationale for the trend and nature of exchange interactions between the spin carriers has been provided. This article confirms the essentially σ nature of the exchange interaction transmitted through the diatomic NO-bridging ligand and the applicability of Goodenough–Kanamori rules, in general, to predict the nature of exchange interactions for different heterometal compounds. The π-conjugated system of the oxime ligand, delocalized over the whole bridging groups and perpendicular to the plane of the oxime ligand, appears to play an important role in the antiferromagnetic interaction between the terminal metal ions, separated by as much as ∼7 A. A comparison of the complexes MAMBMA containing a diamagnetic central ion (MB) clearly indicates the participation of the central metal ion in the transmission of the antiferromagnetic exchange interaction between the terminal paramagnetic MA ions. Competing exchange interactions, or spin frustration in the general sense of the term, in polynuclear complexes may lead to ground-state variability. This type of variable ground-state has been observed for several complexes. The strategy of irregular spin-state structure resulting from a particular spin topology has been found to be more effective, as expected, in obtaining ‘high spin’ molecules than the common strategy of obtaining ferromagnetically coupled systems through involvement of symmetry-related strict orthogonality of the magnetic orbitals of the interacting metal centers. Of particular interest for molecular magnetism is the small but significant effect of bridging ligands like carboxylato anions for cooperation with the ancillary ligand, viz. the oxime ligands, to build up high-nuclearity metal clusters.

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Journal ArticleDOI
TL;DR: The ligand 1,4,7-tris(acetophenoneoxime)-1,4-7-triazacyclononane (H(3)L) has been synthesized and its coordination properties toward Cu, Ni, Co, and Mn(II) in the presence of air have been investigated.
Abstract: The ligand 1,4,7-tris(acetophenoneoxime)-1,4,7-triazacyclononane (H(3)L) has been synthesized and its coordination properties toward Cu(II), Ni(II), Co(II), and Mn(II) in the presence of air have been investigated. Copper(II) yields a mononuclear complex, [Cu(H(2)L)](ClO(4)) (1), cobalt(II) and manganese(II) ions yield mixed-valence Co(III)(2)Co(II) (2a) and Mn(II)(2)Mn(III) (4) complexes, whereas nickel(II) produces a tetranuclear [Ni(4)(HL)(3)](2+) (3) complex. The complexes have been structurally, magnetochemically, and spectroscopically characterized. Complex 3, a planar trigonal-shaped tetranuclear Ni(II) species, exhibits irregular spin-ladder. Variable-temperature (2-290 K) magnetic susceptibility analysis of 3 demonstrates antiferromagnetic exchange interactions (J = -13.4 cm(-1)) between the neighboring Ni(II) ions, which lead to the ground-state S(t) = 2.0 owing to the topology of the spin-carriers in 3. A bulk ferromaganetic interaction (J = +2 cm(-1)) is prevailing between the neighboring high-spin Mn(II) and high-spin Mn(III) ions leading to a ground state of S(t) = 7.0 for 4. The large ground-state spin value of S(t) = 7.0 has been confirmed by magnetization measurements at applied magnetic fields of 1, 4 and 7 T. A bridging monomethyl carbonato ligand formation occurs through an efficient CO(2) uptake from air in methanolic solutions containing a base in the case of complex 4.

59 citations


Journal ArticleDOI
TL;DR: A wattle-type heteropolynuclear complex, which represents the first system with macrocyclic oxamido and alternate azido bridges, forming a one-dimensional chain structure, has been synthesized and characterized by a low temperature magnetic study.
Abstract: A wattle-type heteropolynuclear complex [(CuL)Mn(N3)2]n (1) (H2L = 2,3-dioxo-5,6:15,16-dibenzo-1,4,8,13-tetraazacyclo-pentadeca-7,13-diene), which represents the first system with macrocyclic oxamido and alternate azido bridges, forming a one-dimensional chain structure, has been synthesized and characterized by a low temperature magnetic study. The chains are stacked with interchain hydrogen and lead to the structure of a three-dimensional network.

50 citations


Journal ArticleDOI
TL;DR: Three trinuclear complexes based on (pyridine-2-aldoximato)nickel(II) units are described and display antiferromagnetic exchange coupling of the neighbouring metal centers, while weak ferromagnetic spin exchange between the adjacent Ni II and Cr III ions in is observed.
Abstract: Three trinuclear complexes, NiIIMnIIINiII1, NiIICrIIINiII2 and NiII33 based on (pyridine-2-aldoximato)nickel(II) units are described. Two of them, 1 and 2, contain metal-centers in linear arrangement, as is revealed by X-ray diffraction. Complex 3 is a homonuclear complex in which the three nickel(II) centers are disposed in a triangular fashion. The compounds were characterized by various physical methods including cyclic voltammetric and variable-temperature (2–290 K) susceptibility measurements. Complexes 1 and 3 display antiferromagnetic exchange coupling of the neighbouring metal centers, while weak ferromagnetic spin exchange between the adjacent NiII and CrIII ions in 2 is observed. The experimental magnetic data were simulated by using appropriate models.

49 citations


Journal ArticleDOI
Christopher Uyeda1, Jonas C. Peters1Institutions (1)
TL;DR: Heme-containing nitrite reductases bind and activate nitrite by a mechanism that is proposed to involve interactions with Brønsted acidic residues in the secondary coordination sphere, to model this functionality using synthetic platforms that incorporate a Lewis acidic site.
Abstract: Heme-containing nitrite reductases bind and activate nitrite by a mechanism that is proposed to involve interactions with Bronsted acidic residues in the secondary coordination sphere. To model this functionality using synthetic platforms that incorporate a Lewis acidic site, heterobimetallic CoMg complexes supported by diimine–dioxime ligands are described. The neutral (μ-NO2)CoMg species 3 is synthesized from the [(μ-OAc)(Br)CoMg]+ complex 1 by a sequence of one-electron reduction and ligand substitution reactions. Data are presented for a redox series of nitrite adducts, featuring a conserved μ-(η1-N:η1-O)-NO2 motif, derived from this synthon. Conditions are identified for the proton-induced N–O bond heterolysis of bound NO2– in the most reduced member of this series, affording the [(NO)(Cl)CoMg(H2O)]+ complex 6. Reduction of this complex followed by protonation leads to the evolution of free N2O. On the basis of these stoichiometric reactivity studies, the competence of complex 1 as a NO2– reduction c...

48 citations


References
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Journal ArticleDOI
Abstract: An extension of Furnas's method is described. The variation of intensity of an axial reflection as the crystal is rotated about the goniometer axis is used to give a curve of relative transmission T against azimuthal angle ϕ for the corresponding reciprocal lattice level. Transmission coefficients for any general reflexion hkl are then given approximately by T(hkl) = [T(ϕinc) + T(ϕret)]/2 where ϕinc and ϕret are the azimuthal angles of the incident and reflected beams. Equations are derived for (ϕinc and ϕret and the accuracy of the method is discussed.

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726 citations


Book ChapterDOI
Olivier Kahn1Institutions (1)
Abstract: Publisher Summary The field of heterobimetallic systems has developed tremendously over the past several years particularly in relation to the synthesis of molecular-based magnets This chapter reviews the advancements in the field of bimetallic magnets The chapter also discusses some key concepts in molecular magnetism—as spin delocalization, spin polarization—and the interaction between two spin carriers Several compounds are presented in order of increasing nuclearity and dimensionality The chapter focuses on the bridges that have allowed the design of molecular-based magnets These bridges are oxamato, oxamido, oxalato, dithiooxalato, oximato, and cyano Molecular magnetism has emerged as a novel field of research over the past several years This field concerns the chemistry and the physics of open-shell molecules and molecular assemblies containing open-shell units Among all molecules and molecular assemblies relevant to molecular magnetism, those containing two (or possibly more) kinds of metal ions have played a particularly important role

360 citations